Changeset 6779

Timestamp:

11/09/15 18:01:20 (9 years ago)

Author:

Oliver Schonefeld

Message:

• prepare for SRU 2.0 (add basic version stuff)

Location:

SRUServer/trunk

Files:

• pom.xml (modified) (1 diff)
• src/main/java/eu/clarin/sru/server/SRUNamespaces.java (added)
• src/main/java/eu/clarin/sru/server/SRURequestImpl.java (modified) (8 diffs)
• src/main/java/eu/clarin/sru/server/SRUServer.java (modified) (63 diffs)
• src/main/java/eu/clarin/sru/server/SRUServerConfig.java (modified) (9 diffs)
• src/main/java/eu/clarin/sru/server/SRUVersion.java (modified) (1 diff)

SRUServer/trunk/pom.xml

@@ -17 +17 @@
         <maven.compiler.target>1.6</maven.compiler.target>
         <!-- dependency versions -->
-        <slf4j.version>1.6.4</slf4j.version>
+        <slf4j.version>1.7.12</slf4j.version>
     </properties>
 

SRUServer/trunk/src/main/java/eu/clarin/sru/server/SRURequestImpl.java

@@ -25 +25 @@
 import javax.servlet.http.HttpServletRequest;
 
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
 import org.z3950.zing.cql.CQLNode;
 import org.z3950.zing.cql.CQLParseException;
@@ -31 +33 @@
 
 final class SRURequestImpl implements SRURequest, SRUDiagnosticList {
+    private static final Logger logger =
+            LoggerFactory.getLogger(SRURequest.class);
     private static final String PARAM_OPERATION         = "operation";
     private static final String PARAM_VERSION           = "version";
@@ -195 +199 @@
 
 
+    /**
+     * Validate incoming request parameters.
+     *
+     * @return <code>true</code> if successful, <code>false</code> if something
+     *         went wrong
+     */
     boolean checkParameters() {
-        // parse mandatory operation parameter
-        final String op = getParameter(PARAM_OPERATION, false, false);
-        if (op != null) {
-            if (!op.isEmpty()) {
-                if (op.equals(OP_EXPLAIN)) {
-                    this.operation = SRUOperation.EXPLAIN;
-                } else if (op.equals(OP_SCAN)) {
-                    this.operation = SRUOperation.SCAN;
-                } else if (op.equals(OP_SEARCH_RETRIEVE)) {
-                    this.operation = SRUOperation.SEARCH_RETRIEVE;
+        /*
+         * FIXME: those parameters must be inject from "outside" (probably
+         *        by the appropriate Servlet instance)
+         */
+        final SRUVersion minVersion = config.getMinVersion();
+        final SRUVersion maxVersion = config.getMaxVersion();
+
+        /*
+         * Heuristic to detect SRU version and operation ...
+         */
+        SRUOperation operation = null;
+        SRUVersion version = null;
+        if (maxVersion.compareTo(SRUVersion.VERSION_2_0) >= 0) {
+            if (getParameter(PARAM_VERSION, false, false) == null) {
+                logger.debug("handling request as SRU 2.0, because no '{}' " +
+                        "parameter was found in the request", PARAM_VERSION);
+                if (getParameter(PARAM_QUERY, false, false) != null) {
+                    logger.debug("found parameter '{}' therefore " +
+                            "assuming '{}' operation",
+                            PARAM_QUERY, SRUOperation.SEARCH_RETRIEVE);
+                    operation = SRUOperation.SEARCH_RETRIEVE;
+                } else if (getParameter(PARAM_SCAN_CLAUSE, false, false) != null) {
+                    logger.debug("found parameter '{}' therefore " +
+                            "assuming '{}' operation",
+                            PARAM_SCAN_CLAUSE, SRUOperation.SCAN);
+                    operation = SRUOperation.SCAN;
                 } else {
-                    addDiagnostic(SRUConstants.SRU_UNSUPPORTED_OPERATION, null,
-                            "Operation \"" + op + "\" is not supported.");
+                    logger.debug("no special parameter found therefore " +
+                            "assuming '{}' operation",
+                            SRUOperation.EXPLAIN);
+                    operation = SRUOperation.EXPLAIN;
+                }
+
+                /* record version ... */
+                version = SRUVersion.VERSION_2_0;
+
+                /* do pedantic check for 'operation' parameter */
+                final String op = getParameter(PARAM_OPERATION, false, false);
+                if (op != null) {
+                    /*
+                     * XXX: if operation is searchRetrive an operation parameter,
+                     * is also searchRetrieve, the server may ignore it
+                     */
+                    if (!(operation == SRUOperation.SEARCH_RETRIEVE) &&
+                            op.equals(OP_SEARCH_RETRIEVE)) {
+                        addDiagnostic(SRUConstants.SRU_UNSUPPORTED_PARAMETER,
+                                PARAM_OPERATION, "Parameter '" +
+                                        PARAM_OPERATION +
+                                        "' is not valid for SRU version 2.0");
+                    }
                 }
             } else {
-                addDiagnostic(SRUConstants.SRU_UNSUPPORTED_OPERATION, null,
-                        "An empty parameter \"" + PARAM_OPERATION +
-                                "\" is not supported.");
-            }
-
-            // parse and check version
-            parseAndCheckVersionParameter();
-        } else {
-            /*
-             * absent parameter should be interpreted as "explain"
-             */
-            this.operation = SRUOperation.EXPLAIN;
-
-            // parse and check version
-            parseAndCheckVersionParameter();
-        }
+                logger.debug("handling request as legacy SRU, because found " +
+                        "parameter '{}' in request", PARAM_VERSION);
+
+                // parse mandatory operation parameter
+                final String op = getParameter(PARAM_OPERATION, false, false);
+                if (op != null) {
+                    if (!op.isEmpty()) {
+                        if (op.equals(OP_EXPLAIN)) {
+                            this.operation = SRUOperation.EXPLAIN;
+                        } else if (op.equals(OP_SCAN)) {
+                            this.operation = SRUOperation.SCAN;
+                        } else if (op.equals(OP_SEARCH_RETRIEVE)) {
+                            this.operation = SRUOperation.SEARCH_RETRIEVE;
+                        } else {
+                            addDiagnostic(SRUConstants.SRU_UNSUPPORTED_OPERATION,
+                                    null, "Operation \"" + op + "\" is not supported.");
+                        }
+                    } else {
+                        addDiagnostic(SRUConstants.SRU_UNSUPPORTED_OPERATION,
+                                null, "An empty parameter \"" +
+                                        PARAM_OPERATION +
+                                      "\" is not supported.");
+                    }
+
+                    // parse and check version
+                    version = parseAndCheckVersionParameter(operation);
+                } else {
+                    /*
+                     * absent parameter should be interpreted as "explain"
+                     */
+                    operation = SRUOperation.EXPLAIN;
+
+                    // parse and check version
+                    version = parseAndCheckVersionParameter(operation);
+                }
+            }
+        }
+
+        if ((version == null) || (operation == null)) {
+            logger.error("internal error!!!!1elf");
+        }
+
+        if (minVersion.compareTo(version) < 0) {
+            addDiagnostic(SRUConstants.SRU_UNSUPPORTED_VERSION,
+                    version.getVersionString(), "Version '{}' is not supported by this endpoint");
+        }
+        return checkParameters2();
+    }
+
+
+    boolean checkParameters2() {
 
         if (diagnostics == null) {
@@ -664 +746 @@
 
 
-    private void parseAndCheckVersionParameter() {
+    private SRUVersion parseAndCheckVersionParameter(SRUOperation operation) {
         final String v = getParameter(PARAM_VERSION, true, true);
         if (v != null) {
+            SRUVersion version = null;
             if (v.equals(VERSION_1_1)) {
-                this.version = SRUVersion.VERSION_1_1;
+                version = SRUVersion.VERSION_1_1;
             } else if (v.equals(VERSION_1_2)) {
-                this.version = SRUVersion.VERSION_1_2;
+                version = SRUVersion.VERSION_1_2;
             } else {
                 addDiagnostic(SRUConstants.SRU_UNSUPPORTED_VERSION,
@@ -676 +759 @@
                                 "\" is not supported");
             }
+            return version;
         } else {
             /*
@@ -681 +765 @@
              * parameter was not supplied.
              */
-            if (this.operation != SRUOperation.EXPLAIN) {
+            if (operation != SRUOperation.EXPLAIN) {
                 addDiagnostic(
                         SRUConstants.SRU_MANDATORY_PARAMETER_NOT_SUPPLIED,
@@ -691 +775 @@
              * this is an explain operation, assume default version
              */
-            this.version = config.getDefaultVersion();
+            return config.getDefaultVersion();
         }
     }
@@ -730 +814 @@
                 break;
             case VERSION_1_2:
+                /* FALL-THROUGH */
+            case VERSION_2_0:
                 compat = CQLParser.V1POINT2;
             }

SRUServer/trunk/src/main/java/eu/clarin/sru/server/SRUServer.java

@@ -51 +51 @@
  */
 public final class SRUServer {
-    private static final String SRU_NS =
-            "http://www.loc.gov/zing/srw/";
-    private static final String SRU_PREFIX = "sru";
-    private static final String SRU_DIAGNOSIC_NS =
-            "http://www.loc.gov/zing/srw/diagnostic/";
-    private static final String SRU_DIAGNOSTIC_PREFIX = "diag";
     private static final String SRU_DIAGNOSTIC_RECORD_SCHEMA =
             "info:srw/schema/1/diagnostics-v1.1";
-    private static final String SRU_EXPLAIN_NS =
-            "http://explain.z3950.org/dtd/2.0/";
-    private static final String SRU_EXPLAIN_PREFIX = "zr";
-    private static final String SRU_XCQL_NS =
-            "http://www.loc.gov/zing/cql/xcql/";
     static final String RESPONSE_ENCODING = "utf-8";
     private static final String RESPONSE_CONTENT_TYPE = "application/xml";
@@ -136 +125 @@
                                 SRURecordPacking.XML, false,
                                 req.getIndentResponse());
-                    writeFatalError(out, req, req.getDiagnostics());
+                    final SRUNamespaces ns = getNamespaces(req.getVersion());
+                    writeFatalError(out, ns, req, req.getDiagnostics());
                 }
             } catch (XMLStreamException e) {
@@ -176 +166 @@
                                     SRURecordPacking.XML, false,
                                     req.getIndentResponse());
-                    writeFatalError(out, req, diagnostics);
+                    final SRUNamespaces ns = getNamespaces(req.getVersion());
+                    writeFatalError(out, ns, req, diagnostics);
                 } catch (Exception ex) {
                     logger.error("An exception occurred while in error state",
@@ -205 +196 @@
 
         try {
+            final SRUNamespaces ns = getNamespaces(request.getVersion());
+
             // send results
             SRUXMLStreamWriter out =
@@ -212 +205 @@
                                           request.getIndentResponse());
 
-            beginResponse(out, request);
+            beginResponse(out, ns, request);
 
             // write the explain record
-            writeExplainRecord(out, request);
+            writeExplainRecord(out, ns, request);
 
             if (config.getEchoRequests()) {
-                writeEchoedExplainRequest(out, request);
+                writeEchoedExplainRequest(out, ns, request);
             }
 
             // diagnostics
-            writeDiagnosticList(out, request.getDiagnostics());
+            writeDiagnosticList(out, ns, request.getDiagnostics());
 
             // extraResponseData
             if (result != null) {
                 if (result.hasExtraResponseData()) {
-                    out.writeStartElement(SRU_NS, "extraResponseData");
+                    out.writeStartElement(ns.getResponseNS(), "extraResponseData");
                     result.writeExtraResponseData(out);
                     out.writeEndElement(); // "extraResponseData" element
@@ -256 +249 @@
 
         try {
+            final SRUNamespaces ns = getNamespaces(request.getVersion());
+
+            /*
+             * FIXME: re-check, if while scan response needs to be put
+             * in scan namespace for SRU 2.0!
+             */
             // send results
             SRUXMLStreamWriter out =
@@ -263 +262 @@
                                           request.getIndentResponse());
 
-            beginResponse(out, request);
+            beginResponse(out, ns, request);
 
             try {
@@ -274 +273 @@
                 while (result.nextTerm()) {
                     if (!wroteTerms) {
-                        out.writeStartElement(SRU_NS, "terms");
+                        final boolean needNsDecl =
+                                !ns.getResponseNS().equals(ns.getScanNS());
+                        if (needNsDecl) {
+                            out.setPrefix(ns.getScanPrefix(), ns.getScanNS());
+                        }
+                        out.writeStartElement(ns.getScanNS(), "terms");
+                        if (needNsDecl) {
+                            out.writeNamespace(ns.getScanPrefix(),
+                                    ns.getScanNS());
+                        }
                         wroteTerms = true;
                     }
-                    out.writeStartElement(SRU_NS, "term");
-
-                    out.writeStartElement(SRU_NS, "value");
+                    out.writeStartElement(ns.getScanNS(), "term");
+
+                    out.writeStartElement(ns.getScanNS(), "value");
                     out.writeCharacters(result.getValue());
                     out.writeEndElement(); // "value" element
 
                     if (result.getNumberOfRecords() > -1) {
-                        out.writeStartElement(SRU_NS, "numberOfRecords");
+                        out.writeStartElement(ns.getScanNS(), "numberOfRecords");
                         out.writeCharacters(
                                 Integer.toString(result.getNumberOfRecords()));
@@ -291 +299 @@
 
                     if (result.getDisplayTerm() != null) {
-                        out.writeStartElement(SRU_NS, "displayTerm");
+                        out.writeStartElement(ns.getScanNS(), "displayTerm");
                         out.writeCharacters(result.getDisplayTerm());
                         out.writeEndElement(); // "displayTerm" element
@@ -297 +305 @@
 
                     if (result.getWhereInList() != null) {
-                        out.writeStartElement(SRU_NS, "whereInList");
+                        out.writeStartElement(ns.getScanNS(), "whereInList");
                         switch (result.getWhereInList()) {
                         case FIRST:
@@ -316 +324 @@
 
                     if (result.hasExtraTermData()) {
-                        out.writeStartElement(SRU_NS, "extraTermData");
+                        out.writeStartElement(ns.getScanNS(), "extraTermData");
                         result.writeExtraTermData(out);
                         out.writeEndElement(); // "extraTermData" element
@@ -334 +342 @@
             // echoedScanRequest
             if (config.getEchoRequests()) {
-                writeEchoedScanRequest(out, request, request.getScanClause());
+                writeEchoedScanRequest(out, ns, request, request.getScanClause());
             }
 
             // diagnostics
-            writeDiagnosticList(out, request.getDiagnostics());
+            writeDiagnosticList(out, ns, request.getDiagnostics());
 
             // extraResponseData
             if (result.hasExtraResponseData()) {
-                out.writeStartElement(SRU_NS, "extraResponseData");
+                out.writeStartElement(ns.getResponseNS(), "extraResponseData");
                 result.writeExtraResponseData(out);
                 out.writeEndElement(); // "extraResponseData" element
@@ -381 +389 @@
 
         try {
+            final SRUNamespaces ns = getNamespaces(request.getVersion());
+
             // send results
             SRUXMLStreamWriter out =
@@ -388 +398 @@
                                           request.getIndentResponse());
 
-            beginResponse(out, request);
+            beginResponse(out, ns, request);
 
             // numberOfRecords
-            out.writeStartElement(SRU_NS, "numberOfRecords");
+            out.writeStartElement(ns.getResponseNS(), "numberOfRecords");
             out.writeCharacters(
                     Integer.toString(result.getTotalRecordCount()));
@@ -398 +408 @@
             // resultSetId
             if (result.getResultSetId() != null) {
-                out.writeStartElement(SRU_NS, "resultSetId");
+                out.writeStartElement(ns.getResponseNS(), "resultSetId");
                 out.writeCharacters(result.getResultSetId());
                 out.writeEndElement(); // "resultSetId" element
@@ -405 +415 @@
             // resultSetIdleTime
             if (result.getResultSetIdleTime() > 0) {
-                out.writeStartElement(SRU_NS, "resultSetIdleTime");
+                out.writeStartElement(ns.getResponseNS(), "resultSetIdleTime");
                 out.writeCharacters(Integer.toString(result
                         .getResultSetIdleTime()));
@@ -419 +429 @@
                         : -1;
                 try {
-                    out.writeStartElement(SRU_NS, "records");
+                    out.writeStartElement(ns.getResponseNS(), "records");
                     while (result.nextRecord()) {
                         /*
@@ -435 +445 @@
                         }
 
-                        out.writeStartElement(SRU_NS, "record");
+                        out.writeStartElement(ns.getResponseNS(), "record");
 
                         /*
@@ -445 +455 @@
                                 result.getSurrogateDiagnostic();
 
-                        out.writeStartElement(SRU_NS, "recordSchema");
+                        out.writeStartElement(ns.getResponseNS(), "recordSchema");
                         if (diagnostic == null) {
                             out.writeCharacters(
@@ -455 +465 @@
 
                         // recordPacking
-                        writeRecordPacking(out, request.getRecordPacking());
+                        writeRecordPacking(out, ns, request.getRecordPacking());
 
                         /*
                          * Output either record data or surrogate diagnostic ...
                          */
-                        out.writeStartElement(SRU_NS, "recordData");
+                        out.writeStartElement(ns.getResponseNS(), "recordData");
                         out.startRecord();
                         if (diagnostic == null) {
@@ -466 +476 @@
                         } else {
                             // write a surrogate diagnostic
-                            writeDiagnostic(out, diagnostic, true);
+                            writeDiagnostic(out, ns, diagnostic, true);
                         }
                         out.endRecord();
@@ -478 +488 @@
                                     result.getRecordIdentifier();
                             if (identifier != null) {
-                                out.writeStartElement(SRU_NS,
+                                out.writeStartElement(ns.getResponseNS(),
                                                       "recordIdentifier");
                                 out.writeCharacters(identifier);
@@ -485 +495 @@
                         }
 
-                        out.writeStartElement(SRU_NS, "recordPosition");
+                        out.writeStartElement(ns.getResponseNS(),
+                                "recordPosition");
                         out.writeCharacters(Integer.toString(position));
                         out.writeEndElement(); // "recordPosition" element
 
                         if (result.hasExtraRecordData()) {
-                            out.writeStartElement(SRU_NS, "extraRecordData");
+                            out.writeStartElement(ns.getResponseNS(),
+                                    "extraRecordData");
                             result.writeExtraRecordData(out);
                             out.writeEndElement(); // "extraRecordData"
@@ -510 +522 @@
             // nextRecordPosition
             if (position <= result.getTotalRecordCount()) {
-                out.writeStartElement(SRU_NS, "nextRecordPosition");
+                out.writeStartElement(ns.getResponseNS(), "nextRecordPosition");
                 out.writeCharacters(Integer.toString(position));
                 out.writeEndElement();
@@ -517 +529 @@
             // echoedSearchRetrieveRequest
             if (config.getEchoRequests()) {
-                writeEchoedSearchRetrieveRequest(out, request,
+                writeEchoedSearchRetrieveRequest(out, ns, request,
                                                  request.getQuery());
             }
 
             // diagnostics
-            writeDiagnosticList(out, request.getDiagnostics());
+            writeDiagnosticList(out, ns, request.getDiagnostics());
 
             // extraResponseData
             if (result.hasExtraResponseData()) {
-                out.writeStartElement(SRU_NS, "extraResponseData");
+                out.writeStartElement(ns.getResponseNS(), "extraResponseData");
                 result.writeExtraResponseData(out);
                 out.writeEndElement(); // "extraResponseData" element
@@ -538 +550 @@
 
 
-    private void beginResponse(SRUXMLStreamWriter out, SRUOperation operation,
-            SRUVersion version, String stylesheet) throws XMLStreamException {
+    private void beginResponse(SRUXMLStreamWriter out, SRUNamespaces ns,
+            SRUOperation operation, SRUVersion version, String stylesheet)
+            throws XMLStreamException {
         out.writeStartDocument("utf-8", "1.0");
 
@@ -552 +565 @@
         }
 
-        out.setPrefix(SRU_PREFIX, SRU_NS);
+        out.setPrefix(ns.getResponsePrefix(), ns.getResponseNS());
         switch (operation) {
         case EXPLAIN:
-            out.writeStartElement(SRU_NS, "explainResponse");
+            out.writeStartElement(ns.getResponseNS(), "explainResponse");
             break;
         case SCAN:
-            out.writeStartElement(SRU_NS, "scanResponse");
+            out.writeStartElement(ns.getResponseNS(), "scanResponse");
             break;
         case SEARCH_RETRIEVE:
-            out.writeStartElement(SRU_NS, "searchRetrieveResponse");
+            out.writeStartElement(ns.getResponseNS(), "searchRetrieveResponse");
             break;
         }
-        out.writeNamespace(SRU_PREFIX, SRU_NS);
+        out.writeNamespace(ns.getResponsePrefix(), ns.getResponseNS());
 
         // version
-        writeVersion(out, version);
-    }
-
-
-    private void beginResponse(SRUXMLStreamWriter out, SRURequest request)
-            throws XMLStreamException {
-        beginResponse(out, request.getOperation(), request.getVersion(),
+        writeVersion(out, ns, version);
+    }
+
+
+    private void beginResponse(SRUXMLStreamWriter out, SRUNamespaces ns,
+            SRURequest request) throws XMLStreamException {
+        beginResponse(out, ns, request.getOperation(), request.getVersion(),
                 request.getStylesheet());
     }
@@ -592 +605 @@
 
 
-    private void writeFatalError(SRUXMLStreamWriter out,
+    private void writeFatalError(SRUXMLStreamWriter out, SRUNamespaces ns,
             SRURequestImpl request, List<SRUDiagnostic> diagnotics)
             throws XMLStreamException {
@@ -609 +622 @@
          * write a response which conforms to the schema
          */
-        beginResponse(out, operation, version, null);
+        beginResponse(out, ns, operation, version, null);
         switch (operation) {
         case EXPLAIN:
             // 'explain' requires a complete explain record ...
-            writeExplainRecord(out, request);
+            writeExplainRecord(out, ns, request);
             break;
         case SCAN:
@@ -620 +633 @@
         case SEARCH_RETRIEVE:
             // 'searchRetrieve' needs numberOfRecords ..
-            out.writeStartElement(SRU_NS, "numberOfRecords");
+            out.writeStartElement(ns.getResponseNS(), "numberOfRecords");
             out.writeCharacters("0");
             out.writeEndElement(); // "numberOfRecords" element
             break;
         }
-        writeDiagnosticList(out, diagnotics);
+        writeDiagnosticList(out, ns, diagnotics);
         endResponse(out);
     }
 
 
-    private void writeDiagnosticList(SRUXMLStreamWriter out,
+    private void writeDiagnosticList(SRUXMLStreamWriter out, SRUNamespaces ns,
             List<SRUDiagnostic> diagnostics) throws XMLStreamException {
         if ((diagnostics != null) && !diagnostics.isEmpty()) {
-            out.setPrefix(SRU_DIAGNOSTIC_PREFIX, SRU_DIAGNOSIC_NS);
-            out.writeStartElement(SRU_NS, "diagnostics");
-            out.writeNamespace(SRU_DIAGNOSTIC_PREFIX, SRU_DIAGNOSIC_NS);
+            out.setPrefix(ns.getDiagnosticPrefix(), ns.getDiagnosticNS());
+            out.writeStartElement(ns.getDiagnosticNS(), "diagnostics");
+            out.writeNamespace(ns.getDiagnosticPrefix(), ns.getDiagnosticNS());
             for (SRUDiagnostic diagnostic : diagnostics) {
-                writeDiagnostic(out, diagnostic, false);
+                writeDiagnostic(out, ns, diagnostic, false);
             }
             out.writeEndElement(); // "diagnostics" element
@@ -644 +657 @@
 
 
-    private void writeExplainRecord(SRUXMLStreamWriter out,
+    private void writeExplainRecord(SRUXMLStreamWriter out, SRUNamespaces ns,
             SRURequestImpl request) throws XMLStreamException {
-        out.writeStartElement(SRU_NS, "record");
-
-        out.writeStartElement(SRU_NS, "recordSchema");
-        out.writeCharacters(SRU_EXPLAIN_NS);
+        out.writeStartElement(ns.getResponseNS(), "record");
+
+        out.writeStartElement(ns.getResponseNS(), "recordSchema");
+        out.writeCharacters(ns.getExplainNS());
         out.writeEndElement(); // "recordSchema" element
 
         // recordPacking
-        writeRecordPacking(out, request.getRecordPacking());
-
-        out.writeStartElement(SRU_NS, "recordData");
+        writeRecordPacking(out, ns, request.getRecordPacking());
+
+        out.writeStartElement(ns.getResponseNS(), "recordData");
 
         out.startRecord();
 
         // explain ...
-        out.setPrefix(SRU_EXPLAIN_PREFIX, SRU_EXPLAIN_NS);
-        out.writeStartElement(SRU_EXPLAIN_NS, "explain");
-        out.writeNamespace(SRU_EXPLAIN_PREFIX, SRU_EXPLAIN_NS);
+        out.setPrefix(ns.getExplainPrefix(), ns.getExplainNS());
+        out.writeStartElement(ns.getExplainNS(), "explain");
+        out.writeNamespace(ns.getExplainPrefix(), ns.getExplainNS());
 
         // explain/serverInfo
-        out.writeStartElement(SRU_EXPLAIN_NS, "serverInfo");
+        out.writeStartElement(ns.getExplainNS(), "serverInfo");
         out.writeAttribute("protocol", "SRU");
         switch (config.getDefaultVersion()) {
@@ -673 +686 @@
         case VERSION_1_2:
             out.writeAttribute("version", "1.2");
+            break;
+        case VERSION_2_0:
+            out.writeAttribute("version", "2.0");
+            break;
         } // switch
         out.writeAttribute("transport", config.getTransports());
-        out.writeStartElement(SRU_EXPLAIN_NS, "host");
+        out.writeStartElement(ns.getExplainNS(), "host");
         out.writeCharacters(config.getHost());
         out.writeEndElement(); // "host" element
-        out.writeStartElement(SRU_EXPLAIN_NS, "port");
+        out.writeStartElement(ns.getExplainNS(), "port");
         out.writeCharacters(Integer.toString(config.getPort()));
         out.writeEndElement(); // "port" element
-        out.writeStartElement(SRU_EXPLAIN_NS, "database");
+        out.writeStartElement(ns.getExplainNS(), "database");
         out.writeCharacters(config.getDatabase());
         out.writeEndElement(); // "database" element
@@ -689 +706 @@
         final DatabaseInfo dbinfo = config.getDatabaseInfo();
         if (dbinfo != null) {
-            out.writeStartElement(SRU_EXPLAIN_NS, "databaseInfo");
-            writeLocalizedStrings(out, "title", dbinfo.getTitle());
-            writeLocalizedStrings(out, "description", dbinfo.getDescription());
-            writeLocalizedStrings(out, "author", dbinfo.getAuthor());
-            writeLocalizedStrings(out, "extent", dbinfo.getExtend());
-            writeLocalizedStrings(out, "history", dbinfo.getHistory());
-            writeLocalizedStrings(out, "langUsage", dbinfo.getLangUsage());
-            writeLocalizedStrings(out, "restrictions", dbinfo.getRestrictions());
-            writeLocalizedStrings(out, "subjects", dbinfo.getSubjects());
-            writeLocalizedStrings(out, "links", dbinfo.getLinks());
-            writeLocalizedStrings(out, "implementation",
+            out.writeStartElement(ns.getExplainNS(), "databaseInfo");
+            writeLocalizedStrings(out, ns, "title",
+                    dbinfo.getTitle());
+            writeLocalizedStrings(out, ns, "description",
+                    dbinfo.getDescription());
+            writeLocalizedStrings(out, ns, "author",
+                    dbinfo.getAuthor());
+            writeLocalizedStrings(out, ns, "extent",
+                    dbinfo.getExtend());
+            writeLocalizedStrings(out, ns, "history",
+                    dbinfo.getHistory());
+            writeLocalizedStrings(out, ns, "langUsage",
+                    dbinfo.getLangUsage());
+            writeLocalizedStrings(out, ns, "restrictions",
+                    dbinfo.getRestrictions());
+            writeLocalizedStrings(out, ns, "subjects",
+                    dbinfo.getSubjects());
+            writeLocalizedStrings(out, ns, "links",
+                    dbinfo.getLinks());
+            writeLocalizedStrings(out, ns, "implementation",
                     dbinfo.getImplementation());
             out.writeEndElement(); // "databaseInfo" element
@@ -707 +733 @@
         final IndexInfo indexInfo = config.getIndexInfo();
         if (indexInfo != null) {
-            out.writeStartElement(SRU_EXPLAIN_NS, "indexInfo");
+            out.writeStartElement(ns.getExplainNS(), "indexInfo");
 
             List<IndexInfo.Set> sets = indexInfo.getSets();
             if (sets != null) {
                 for (IndexInfo.Set set : sets) {
-                    out.writeStartElement(SRU_EXPLAIN_NS, "set");
+                    out.writeStartElement(ns.getExplainNS(), "set");
                     out.writeAttribute("identifier", set.getIdentifier());
                     out.writeAttribute("name", set.getName());
-                    writeLocalizedStrings(out, "title", set.getTitle());
+                    writeLocalizedStrings(out, ns, "title", set.getTitle());
                     out.writeEndElement(); // "set" element
                 }
@@ -723 +749 @@
             if (indexes != null) {
                 for (IndexInfo.Index index : indexes) {
-                    out.writeStartElement(SRU_EXPLAIN_NS, "index");
+                    out.writeStartElement(ns.getExplainNS(), "index");
                     out.writeAttribute("search",
                             index.canSearch() ? "true" : "false");
@@ -730 +756 @@
                     out.writeAttribute("sort",
                             index.canSort() ? "true" : "false");
-                    writeLocalizedStrings(out, "title", index.getTitle());
+                    writeLocalizedStrings(out, ns, "title", index.getTitle());
                     List<IndexInfo.Index.Map> maps = index.getMaps();
                     if (maps != null) {
                         for (IndexInfo.Index.Map map : maps) {
-                            out.writeStartElement(SRU_EXPLAIN_NS, "map");
+                            out.writeStartElement(ns.getExplainNS(), "map");
                             if (map.isPrimary()) {
                                 out.writeAttribute("primary", "true");
                             }
-                            out.writeStartElement(SRU_EXPLAIN_NS, "name");
+                            out.writeStartElement(ns.getExplainNS(), "name");
                             out.writeAttribute("set", map.getSet());
                             out.writeCharacters(map.getName());
@@ -755 +781 @@
                 config.getSchemaInfo();
         if (schemaInfo != null) {
-            out.writeStartElement(SRU_EXPLAIN_NS, "schemaInfo");
+            out.writeStartElement(ns.getExplainNS(), "schemaInfo");
             for (SRUServerConfig.SchemaInfo schema : schemaInfo) {
-                out.writeStartElement(SRU_EXPLAIN_NS, "schema");
+                out.writeStartElement(ns.getExplainNS(), "schema");
                 out.writeAttribute("identifier", schema.getIdentifier());
                 out.writeAttribute("name", schema.getName());
@@ -772 +798 @@
                     out.writeAttribute("retrieve", "false");
                 }
-                writeLocalizedStrings(out, "title", schema.getTitle());
+                writeLocalizedStrings(out, ns, "title", schema.getTitle());
                 out.writeEndElement(); // "schema" element
             }
@@ -779 +805 @@
 
         // explain/configInfo
-        out.writeStartElement(SRU_EXPLAIN_NS, "configInfo");
+        out.writeStartElement(ns.getExplainNS(), "configInfo");
         // numberOfRecords (default)
-        out.writeStartElement(SRU_EXPLAIN_NS, "default");
+        out.writeStartElement(ns.getExplainNS(), "default");
         out.writeAttribute("type", "numberOfRecords");
         out.writeCharacters(Integer.toString(config.getNumberOfRecords()));
@@ -787 +813 @@
 
         // maximumRecords (setting)
-        out.writeStartElement(SRU_EXPLAIN_NS, "setting");
+        out.writeStartElement(ns.getExplainNS(), "setting");
         out.writeAttribute("type", "maximumRecords");
         out.writeCharacters(Integer.toString(config.getMaximumRecords()));
@@ -803 +829 @@
 
 
-    private void writeDiagnostic(SRUXMLStreamWriter out,
+    private void writeDiagnostic(SRUXMLStreamWriter out, SRUNamespaces ns,
             SRUDiagnostic diagnostic, boolean writeNsDecl)
             throws XMLStreamException {
         if (writeNsDecl) {
-            out.setPrefix(SRU_DIAGNOSTIC_PREFIX, SRU_DIAGNOSIC_NS);
-        }
-        out.writeStartElement(SRU_DIAGNOSIC_NS, "diagnostic");
+            out.setPrefix(ns.getDiagnosticPrefix(), ns.getDiagnosticNS());
+        }
+        out.writeStartElement(ns.getDiagnosticNS(), "diagnostic");
         if (writeNsDecl) {
-            out.writeNamespace(SRU_DIAGNOSTIC_PREFIX, SRU_DIAGNOSIC_NS);
-        }
-        out.writeStartElement(SRU_DIAGNOSIC_NS, "uri");
+            out.writeNamespace(ns.getDiagnosticPrefix(), ns.getDiagnosticNS());
+        }
+        out.writeStartElement(ns.getDiagnosticNS(), "uri");
         out.writeCharacters(diagnostic.getURI());
         out.writeEndElement(); // "uri" element
         if (diagnostic.getDetails() != null) {
-            out.writeStartElement(SRU_DIAGNOSIC_NS, "details");
+            out.writeStartElement(ns.getDiagnosticNS(), "details");
             out.writeCharacters(diagnostic.getDetails());
             out.writeEndElement(); // "details" element
         }
         if (diagnostic.getMessage() != null) {
-            out.writeStartElement(SRU_DIAGNOSIC_NS, "message");
+            out.writeStartElement(ns.getDiagnosticNS(), "message");
             out.writeCharacters(diagnostic.getMessage());
             out.writeEndElement(); // "message" element
@@ -831 +857 @@
 
     private void writeEchoedExplainRequest(SRUXMLStreamWriter out,
-            SRURequestImpl request) throws XMLStreamException,
-            SRUException {
+            SRUNamespaces ns, SRURequestImpl request)
+            throws XMLStreamException, SRUException {
         // echoedSearchRetrieveRequest
-        out.writeStartElement(SRU_NS, "echoedExplainRequest");
+        out.writeStartElement(ns.getResponseNS(), "echoedExplainRequest");
 
         // echoedExplainRequest/version
         if (request.getRawVersion() != null) {
-            writeVersion(out, request.getRawVersion());
+            writeVersion(out, ns, request.getRawVersion());
         }
 
         // echoedExplainRequest/recordPacking
         if (request.getRawRecordPacking() != null) {
-            writeRecordPacking(out, request.getRawRecordPacking());
+            writeRecordPacking(out, ns, request.getRawRecordPacking());
         }
 
         // echoedExplainRequest/stylesheet
         if (request.getStylesheet() != null) {
-            out.writeStartElement(SRU_NS, "stylesheet");
+            out.writeStartElement(ns.getResponseNS(), "stylesheet");
             out.writeCharacters(request.getStylesheet());
             out.writeEndElement(); // "stylesheet" element
@@ -855 +881 @@
         // echoedExplainRequest/baseUrl (SRU 1.2 only)
         if (request.isVersion(SRUVersion.VERSION_1_2)) {
-            writeBaseUrl(out, request);
+            writeBaseUrl(out, ns, request);
         }
 
@@ -863 +889 @@
 
     private void writeEchoedScanRequest(SRUXMLStreamWriter out,
-            SRURequestImpl request, CQLNode cql) throws XMLStreamException,
-            SRUException {
+            SRUNamespaces ns, SRURequestImpl request, CQLNode cql)
+            throws XMLStreamException, SRUException {
         // echoedScanRequest
-        out.writeStartElement(SRU_NS, "echoedScanRequest");
+        out.writeStartElement(ns.getResponseNS(), "echoedScanRequest");
 
         // echoedScanRequest/version
         if (request.getRawVersion() != null) {
-            writeVersion(out, request.getRawVersion());
+            writeVersion(out, ns, request.getRawVersion());
         }
 
         // echoedScanRequest/scanClause
-        out.writeStartElement(SRU_NS, "scanClause");
+        out.writeStartElement(ns.getResponseNS(), "scanClause");
         out.writeCharacters(request.getRawScanClause());
         out.writeEndElement(); // "query"
 
         // echoedScanRequest/xScanClause
-        out.setDefaultNamespace(SRU_XCQL_NS);
-        out.writeStartElement(SRU_NS, "xScanClause");
-        out.writeDefaultNamespace(SRU_XCQL_NS);
+        out.setDefaultNamespace(ns.getXcqlNS());
+        out.writeStartElement(ns.getResponseNS(), "xScanClause");
+        out.writeDefaultNamespace(ns.getXcqlNS());
         out.writeXCQL(cql, false);
         out.writeEndElement(); // "xScanClause" element
@@ -887 +913 @@
         // echoedScanRequest/responsePosition
         if (request.getResponsePosition() != -1) {
-            out.writeStartElement(SRU_NS, "responsePosition");
+            out.writeStartElement(ns.getResponseNS(), "responsePosition");
             out.writeCharacters(
                     Integer.toString(request.getResponsePosition()));
@@ -895 +921 @@
         // echoedScanRequest/maximumTerms
         if (request.getMaximumTerms() != -1) {
-            out.writeStartElement(SRU_NS, "maximumTerms");
+            out.writeStartElement(ns.getResponseNS(), "maximumTerms");
             out.writeCharacters(Integer.toString(request.getMaximumTerms()));
             out.writeEndElement(); // "maximumTerms" element
@@ -902 +928 @@
         // echoedScanRequest/stylesheet
         if (request.getStylesheet() != null) {
-            out.writeStartElement(SRU_NS, "stylesheet");
+            out.writeStartElement(ns.getResponseNS(), "stylesheet");
             out.writeCharacters(request.getStylesheet());
             out.writeEndElement(); // "stylesheet" element
@@ -909 +935 @@
         // echoedScanRequest/baseUrl (SRU 1.2 only)
         if (request.isVersion(SRUVersion.VERSION_1_2)) {
-            writeBaseUrl(out, request);
+            writeBaseUrl(out, ns, request);
         }
 
@@ -917 +943 @@
 
     private void writeEchoedSearchRetrieveRequest(SRUXMLStreamWriter out,
-            SRURequestImpl request, CQLNode cql) throws XMLStreamException,
-            SRUException {
+            SRUNamespaces ns, SRURequestImpl request, CQLNode cql)
+            throws XMLStreamException, SRUException {
         // echoedSearchRetrieveRequest
-        out.writeStartElement(SRU_NS, "echoedSearchRetrieveRequest");
+        out.writeStartElement(ns.getResponseNS(),
+                "echoedSearchRetrieveRequest");
 
         // echoedSearchRetrieveRequest/version
         if (request.getRawVersion() != null) {
-            writeVersion(out, request.getRawVersion());
+            writeVersion(out, ns, request.getRawVersion());
         }
 
         // echoedSearchRetrieveRequest/query
-        out.writeStartElement(SRU_NS, "query");
+        out.writeStartElement(ns.getResponseNS(), "query");
         out.writeCharacters(request.getRawQuery());
         out.writeEndElement(); // "query"
 
         // echoedSearchRetrieveRequest/xQuery
-        out.setDefaultNamespace(SRU_XCQL_NS);
-        out.writeStartElement(SRU_NS, "xQuery");
-        out.writeDefaultNamespace(SRU_XCQL_NS);
+        out.setDefaultNamespace(ns.getXcqlNS());
+        out.writeStartElement(ns.getResponseNS(), "xQuery");
+        out.writeDefaultNamespace(ns.getXcqlNS());
         out.writeXCQL(cql, true);
         out.writeEndElement(); // "xQuery" element
@@ -941 +968 @@
         // echoedSearchRetrieveRequest/startRecord
         if (request.getStartRecord() > 0) {
-            out.writeStartElement(SRU_NS, "startRecord");
+            out.writeStartElement(ns.getResponseNS(), "startRecord");
             out.writeCharacters(Integer.toString(request.getStartRecord()));
             out.writeEndElement(); // "startRecord" element
@@ -948 +975 @@
         // echoedSearchRetrieveRequest/maximumRecords
         if (request.getRawMaximumRecords() > 0) {
-            out.writeStartElement(SRU_NS, "maximumRecords");
+            out.writeStartElement(ns.getResponseNS(), "maximumRecords");
             out.writeCharacters(
                     Integer.toString(request.getRawMaximumRecords()));
@@ -956 +983 @@
         // echoedSearchRetrieveRequest/recordPacking
         if (request.getRawRecordPacking() != null) {
-            writeRecordPacking(out, request.getRawRecordPacking());
+            writeRecordPacking(out, ns, request.getRawRecordPacking());
         }
 
         // echoedSearchRetrieveRequest/recordSchema
         if (request.getRawRecordSchemaIdentifier() != null) {
-            out.writeStartElement(SRU_NS, "recordSchema");
+            out.writeStartElement(ns.getResponseNS(), "recordSchema");
             out.writeCharacters(request.getRawRecordSchemaIdentifier());
             out.writeEndElement(); // "recordSchema" element
@@ -969 +996 @@
         if (request.isVersion(SRUVersion.VERSION_1_1) &&
                 (request.getRecordXPath() != null)) {
-            out.writeStartElement(SRU_NS, "recordXPath");
+            out.writeStartElement(ns.getResponseNS(), "recordXPath");
             out.writeCharacters(request.getRecordXPath());
             out.writeEndElement(); // "recordXPath" element
@@ -976 +1003 @@
         // echoedSearchRetrieveRequest/resultSetTTL
         if (request.getResultSetTTL() > 0) {
-            out.writeStartElement(SRU_NS, "resultSetTTL");
+            out.writeStartElement(ns.getResponseNS(), "resultSetTTL");
             out.writeCharacters(Long.toString(request.getResultSetTTL()));
             out.writeEndElement(); // "resultSetTTL" element
@@ -984 +1011 @@
         if (request.isVersion(SRUVersion.VERSION_1_1) &&
                 (request.getSortKeys() != null)) {
-            out.writeStartElement(SRU_NS, "sortKeys");
+            out.writeStartElement(ns.getResponseNS(), "sortKeys");
             out.writeCharacters(request.getSortKeys());
             out.writeEndElement(); // "sortKeys" element
@@ -993 +1020 @@
         // echoedSearchRetrieveRequest/stylesheet
         if (request.getStylesheet() != null) {
-            out.writeStartElement(SRU_NS, "stylesheet");
+            out.writeStartElement(ns.getResponseNS(), "stylesheet");
             out.writeCharacters(request.getStylesheet());
             out.writeEndElement(); // "stylesheet" element
@@ -1000 +1027 @@
         // echoedSearchRetrieveRequest/baseUrl (SRU 1.2 only)
         if (request.isVersion(SRUVersion.VERSION_1_2)) {
-            writeBaseUrl(out, request);
+            writeBaseUrl(out, ns, request);
         }
 
@@ -1007 +1034 @@
 
 
-    private void writeVersion(SRUXMLStreamWriter out, SRUVersion version)
-            throws XMLStreamException {
-        out.writeStartElement(SRU_NS, "version");
+    private void writeVersion(SRUXMLStreamWriter out, SRUNamespaces ns,
+            SRUVersion version) throws XMLStreamException {
+        out.writeStartElement(ns.getResponseNS(), "version");
         switch (version) {
         case VERSION_1_1:
@@ -1017 +1044 @@
             out.writeCharacters("1.2");
             break;
+        case VERSION_2_0:
+            out.writeCharacters("2.0");
+            break;
         } // switch
         out.writeEndElement(); // "version" element
@@ -1022 +1052 @@
 
 
-    private void writeRecordPacking(SRUXMLStreamWriter out,
+    private void writeRecordPacking(SRUXMLStreamWriter out, SRUNamespaces ns,
             SRURecordPacking recordPacking) throws XMLStreamException {
-        out.writeStartElement(SRU_NS, "recordPacking");
+        out.writeStartElement(ns.getResponseNS(), "recordPacking");
         switch (recordPacking) {
         case XML:
@@ -1037 +1067 @@
 
 
-    private void writeBaseUrl(SRUXMLStreamWriter out,
+    private void writeBaseUrl(SRUXMLStreamWriter out, SRUNamespaces ns,
             SRURequest request) throws XMLStreamException {
-        out.writeStartElement(SRU_NS, "baseUrl");
+        out.writeStartElement(ns.getResponseNS(), "baseUrl");
         out.writeCharacters(request.getProtocolScheme());
         out.writeCharacters(config.getBaseUrl());
@@ -1046 +1076 @@
 
 
-    private void writeLocalizedStrings(XMLStreamWriter writer, String name,
-            List<LocalizedString> list) throws XMLStreamException {
+    private void writeLocalizedStrings(XMLStreamWriter writer,
+            SRUNamespaces ns, String name, List<LocalizedString> list)
+            throws XMLStreamException {
         if ((list != null) && !list.isEmpty()) {
             for (LocalizedString item : list) {
-                writer.writeStartElement(SRU_EXPLAIN_NS, name);
+                writer.writeStartElement(ns.getExplainNS(), name);
                 if (item.getLang() != null) {
                     writer.writeAttribute("lang", item.getLang());
@@ -1101 +1132 @@
     }
 
-} // class SRUService
+
+    private SRUNamespaces getNamespaces(SRUVersion version) {
+        if (version == null) {
+            throw new NullPointerException("version == null");
+        }
+        switch (version) {
+        case VERSION_1_1:
+            /* FALL-THROUGH */
+        case VERSION_1_2:
+            return NAMESPACES_LEGACY;
+        case VERSION_2_0:
+            return NAMESPACES_2_0;
+        default:
+            // FIXME: better exception?
+            throw new IllegalAccessError("invalid version: " + version);
+        }
+    }
+
+
+
+
+    private static final SRUNamespaces NAMESPACES_LEGACY = new SRUNamespaces() {
+        private static final String SRU_NS =
+                "http://www.loc.gov/zing/srw/";
+        private static final String SRU_PREFIX =
+                "sru";
+        private static final String SRU_DIAGNOSIC_NS =
+                "http://www.loc.gov/zing/srw/diagnostic/";
+        private static final String SRU_DIAGNOSTIC_PREFIX =
+                "diag";
+        private static final String SRU_EXPLAIN_NS =
+                "http://explain.z3950.org/dtd/2.0/";
+        private static final String SRU_EXPLAIN_PREFIX =
+                "zr";
+        private static final String SRU_XCQL_NS =
+                "http://www.loc.gov/zing/cql/xcql/";
+
+
+        @Override
+        public String getResponseNS() {
+            return SRU_NS;
+        }
+
+
+        @Override
+        public String getResponsePrefix() {
+            return SRU_PREFIX;
+        }
+
+
+        @Override
+        public String getScanNS() {
+            return SRU_NS;
+        }
+
+
+        @Override
+        public String getScanPrefix() {
+            return SRU_PREFIX;
+        }
+
+
+        @Override
+        public String getDiagnosticNS() {
+            return SRU_DIAGNOSIC_NS;
+        }
+
+
+        @Override
+        public String getDiagnosticPrefix() {
+            return SRU_DIAGNOSTIC_PREFIX;
+        }
+
+
+        @Override
+        public String getExplainNS() {
+            return SRU_EXPLAIN_NS;
+        }
+
+
+        @Override
+        public String getExplainPrefix() {
+            return SRU_EXPLAIN_PREFIX;
+        }
+
+
+        @Override
+        public String getXcqlNS() {
+            return SRU_XCQL_NS;
+        }
+    };
+
+
+    private static final SRUNamespaces NAMESPACES_2_0 = new SRUNamespaces() {
+        private static final String SRU_RESPONSE_NS =
+                "http://docs.oasis-open.org/ns/search-ws/sruResponse";
+        private static final String SRU_RESPONSE_PREFIX =
+                "sruResponse";
+        private static final String SRU_SCAN_NS =
+                "http://docs.oasis-open.org/ns/search-ws/scan";
+        private static final String SRU_SCAN_PREFIX =
+                "scan";
+        private static final String SRU_DIAGNOSIC_NS =
+                "http://docs.oasis-open.org/ns/search-ws/diagnostic";
+        private static final String SRU_DIAGNOSTIC_PREFIX =
+                "diag";
+        private static final String SRU_EXPLAIN_NS =
+                "http://explain.z3950.org/dtd/2.0/";
+        private static final String SRU_EXPLAIN_PREFIX =
+                "zr";
+        private static final String SRU_XCQL_NS =
+                "http://docs.oasis-open.org/ns/search-ws/xcql";
+
+
+        @Override
+        public String getResponseNS() {
+            return SRU_RESPONSE_NS;
+        }
+
+
+        @Override
+        public String getResponsePrefix() {
+            return SRU_RESPONSE_PREFIX;
+        }
+
+
+        @Override
+        public String getScanNS() {
+            return SRU_SCAN_NS;
+        }
+
+
+        @Override
+        public String getScanPrefix() {
+            return SRU_SCAN_PREFIX;
+        }
+
+
+        @Override
+        public String getDiagnosticNS() {
+            return SRU_DIAGNOSIC_NS;
+        }
+
+
+        @Override
+        public String getDiagnosticPrefix() {
+            return SRU_DIAGNOSTIC_PREFIX;
+        }
+
+
+        @Override
+        public String getExplainNS() {
+            return SRU_EXPLAIN_NS;
+        }
+
+
+        @Override
+        public String getExplainPrefix() {
+            return SRU_EXPLAIN_PREFIX;
+        }
+
+
+        @Override
+        public String getXcqlNS() {
+            return SRU_XCQL_NS;
+        }
+    };
+
+} // class SRUServer

SRUServer/trunk/src/main/java/eu/clarin/sru/server/SRUServerConfig.java

@@ -86 +86 @@
 public final class SRUServerConfig {
     /**
+     * Parameter constant for setting the minimum supported SRU version for this
+     * SRU server. Must be smaller or equal to {@link #SRU_SUPPORTED_VERSION_MAX}.
+     * <p>
+     * Valid values: "<code>1.1</code>", "<code>1.2</code>" or "
+     * <code>2.0</code>" (without quotation marks)
+     * <p>
+     */
+    public static final String SRU_SUPPORTED_VERSION_MIN =
+            "eu.clarin.sru.server.sruSupportedVersionMin";
+    /**
+     * Parameter constant for setting the maximum supported SRU version for this
+     * SRU server. Must be larger or equal to {@link #SRU_SUPPORTED_VERSION_MIN}.
+     * <p>
+     * Valid values: "<code>1.1</code>", "<code>1.2</code>" or "
+     * <code>2.0</code>" (without quotation marks)
+     * <p>
+     */
+    public static final String SRU_SUPPORTED_VERSION_MAX =
+            "eu.clarin.sru.server.sruSupportedVersionMax";
+    /**
+     * Parameter constant for setting the default SRU version for this SRU
+     * server, e.g. for an <em>Explain</em> request without explicit version.
+     * Must not me less than {@link #SRU_SUPPORTED_VERSION_MIN} or larger than
+     * {@link #SRU_SUPPORTED_VERSION_MAX}. Defaults to
+     * {@link #SRU_SUPPORTED_VERSION_MAX}.
+     * <p>
+     * Valid values: "<code>1.1</code>", "<code>1.2</code>" or "
+     * <code>2.0</code>" (without quotation marks)
+     * <p>
+     */
+    public static final String SRU_SUPPORTED_VERSION_DEFAULT =
+            "eu.clarin.sru.server.sruSupportedVersionDefault";
+    /**
      * Parameter constant for configuring the transports for this SRU server.
      * <p>
@@ -293 +326 @@
     private static final String LEGACY_SRU_ALLOW_OVERRIDE_INDENT_RESPONSE =
             "sru.allowOverrideIndentResponse";
+    private static final SRUVersion DEFAULT_SRU_VERSION_MIN =
+            SRUVersion.VERSION_1_1;
+    private static final SRUVersion DEFAULT_SRU_VERSION_MAX =
+            SRUVersion.VERSION_1_2;
     private static final int DEFAULT_NUMBER_OF_RECORDS    = 100;
     private static final int DEFAULT_MAXIMUM_RECORDS      = 250;
@@ -627 +664 @@
     private static final Logger logger =
             LoggerFactory.getLogger(SRUServerConfig.class);
+    private final SRUVersion minVersion;
+    private final SRUVersion maxVersion;
+    private final SRUVersion defaultVersion;
     private final String transport;
     private final String host;
@@ -647 +687 @@
 
 
-    private SRUServerConfig(String transport, String host, int port,
+    private SRUServerConfig(SRUVersion minVersion, SRUVersion maxVersion,
+            SRUVersion defaultVersion, String transport, String host, int port,
             String database, int numberOfRecords, int maximumRecords,
             int numberOfTerms, int maximumTerms, boolean echoRequests,
@@ -655 +696 @@
             boolean allowOverrideIndentResponse, DatabaseInfo databaseinfo,
             IndexInfo indexInfo, List<SchemaInfo> schemaInfo) {
+        this.minVersion                  = minVersion;
+        this.maxVersion                  = maxVersion;
+        this.defaultVersion              = defaultVersion;
         this.transport                   = transport;
         this.host                        = host;
@@ -688 +732 @@
 
 
+    public SRUVersion getMinVersion() {
+        return minVersion;
+    }
+
+
+    public SRUVersion getMaxVersion() {
+        return maxVersion;
+    }
+
+
     public SRUVersion getDefaultVersion() {
-        return SRUVersion.VERSION_1_2;
+        return defaultVersion;
     }
 
@@ -937 +991 @@
 
             /*
-             * fetch parameters more parameters
+             * fetch parameters more parameters (usually passed from Servlet
+             * context)
              */
+
+            SRUVersion minVersion = parseVersionNumber(params,
+                    SRU_SUPPORTED_VERSION_MIN, false, DEFAULT_SRU_VERSION_MIN);
+
+            SRUVersion maxVersion = parseVersionNumber(params,
+                    SRU_SUPPORTED_VERSION_MAX, false, DEFAULT_SRU_VERSION_MAX);
+            if (maxVersion.compareTo(minVersion) < 0) {
+                throw new SRUConfigException(
+                        "parameter value \"" + SRU_SUPPORTED_VERSION_MAX +
+                                "\" (" + maxVersion.getVersionString() +
+                                ") must be equal or larger than value of parameter \"" +
+                                SRU_SUPPORTED_VERSION_MIN + "\" (" +
+                                minVersion.getVersionString() + ")");
+            }
+
+            SRUVersion defaultVersion = parseVersionNumber(params,
+                    SRU_SUPPORTED_VERSION_DEFAULT, false, maxVersion);
+            if ((defaultVersion.compareTo(minVersion) < 0) ||
+                    (defaultVersion.compareTo(maxVersion) > 0)) {
+                throw new SRUConfigException(
+                        "parameter value \"" + SRU_SUPPORTED_VERSION_DEFAULT +
+                                "\" (" + defaultVersion.getVersionString() +
+                                ") must be between value of parameter \"" +
+                                SRU_SUPPORTED_VERSION_MIN + "\" (" +
+                                minVersion.getVersionString() + ") and \"" +
+                                SRU_SUPPORTED_VERSION_MAX + "\" (" +
+                                maxVersion.getVersionString() + ")");
+            }
+
             String transport = params.get(SRU_TRANSPORT);
             if ((transport == null) || transport.isEmpty()) {
@@ -1011 +1095 @@
                     DEFAULT_RESPONSE_BUFFER_SIZE, 0, -1);
 
-            return new SRUServerConfig(transport, host, port, database,
-                    numberOfRecords, maximumRecords, numberOfTerms,
-                    maximumTerms, echoRequests, indentResponse,
-                    responseBufferSize, allowOverrideMaximumRecords,
-                    allowOverrideMaximumTerms, allowOverrideIndentResponse,
-                    databaseInfo, indexInfo, schemaInfo);
+            return new SRUServerConfig(minVersion, maxVersion, defaultVersion,
+                    transport, host, port, database, numberOfRecords,
+                    maximumRecords, numberOfTerms, maximumTerms, echoRequests,
+                    indentResponse, responseBufferSize,
+                    allowOverrideMaximumRecords, allowOverrideMaximumTerms,
+                    allowOverrideIndentResponse, databaseInfo, indexInfo,
+                    schemaInfo);
         } catch (IOException e) {
             throw new SRUConfigException("error reading configuration file", e);
@@ -1025 +1110 @@
         } catch (SAXException e) {
             throw new SRUConfigException("error parsing configuration file", e);
+        }
+    }
+
+
+    private static SRUVersion parseVersionNumber(Map<String, String> params,
+            String name, boolean mandatory, SRUVersion defaultValue)
+                    throws SRUConfigException {
+        String value = params.get(name);
+        if ((value == null) || value.isEmpty()) {
+            if (mandatory) {
+                throw new SRUConfigException(
+                        "parameter \"" + name + "\" is mandatory");
+            } else {
+                return defaultValue;
+            }
+        } else {
+            if ("1.1".equals(value)) {
+                return SRUVersion.VERSION_1_1;
+            } else if ("1.2".equals(value)) {
+                return SRUVersion.VERSION_1_2;
+            } else if ("2.0".equals(value)) {
+                return SRUVersion.VERSION_2_0;
+            } else {
+                throw new SRUConfigException("invalid value for parameter \"" +
+                        name + "\": " + value);
+            }
         }
     }

SRUServer/trunk/src/main/java/eu/clarin/sru/server/SRUVersion.java

@@ -51 +51 @@
             return "1.2";
         }
+    },
+
+    /**
+     * SRU/CQL version 2.0
+     */
+    VERSION_2_0 {
+        @Override
+        int getVersionNumber() {
+            return ((2 << 16) | 0);
+        }
+
+
+        @Override
+        String getVersionString() {
+            return "2.0";
+        }
     };