001    /**
002     * Licensed to the Apache Software Foundation (ASF) under one
003     * or more contributor license agreements.  See the NOTICE file
004     * distributed with this work for additional information
005     * regarding copyright ownership.  The ASF licenses this file
006     * to you under the Apache License, Version 2.0 (the
007     * "License"); you may not use this file except in compliance
008     * with the License.  You may obtain a copy of the License at
009     *
010     *     http://www.apache.org/licenses/LICENSE-2.0
011     *
012     * Unless required by applicable law or agreed to in writing, software
013     * distributed under the License is distributed on an "AS IS" BASIS,
014     * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
015     * See the License for the specific language governing permissions and
016     * limitations under the License.
017     */
018    package org.apache.hadoop.hdfs.tools.offlineImageViewer;
019    
020    import java.io.IOException;
021    import java.util.LinkedList;
022    
023    /**
024     * An XmlImageVisitor walks over an fsimage structure and writes out
025     * an equivalent XML document that contains the fsimage's components.
026     */
027    public class XmlImageVisitor extends TextWriterImageVisitor {
028      final private LinkedList<ImageElement> tagQ =
029                                              new LinkedList<ImageElement>();
030    
031      public XmlImageVisitor(String filename) throws IOException {
032        super(filename, false);
033      }
034    
035      public XmlImageVisitor(String filename, boolean printToScreen)
036           throws IOException {
037        super(filename, printToScreen);
038      }
039    
040      @Override
041      void finish() throws IOException {
042        super.finish();
043      }
044    
045      @Override
046      void finishAbnormally() throws IOException {
047        write("\n<!-- Error processing image file.  Exiting -->\n");
048        super.finishAbnormally();
049      }
050    
051      @Override
052      void leaveEnclosingElement() throws IOException {
053        if(tagQ.size() == 0)
054          throw new IOException("Tried to exit non-existent enclosing element " +
055                    "in FSImage file");
056    
057        ImageElement element = tagQ.pop();
058        write("</" + element.toString() + ">\n");
059      }
060    
061      @Override
062      void start() throws IOException {
063        write("<?xml version=\"1.0\" ?>\n");
064      }
065    
066      @Override
067      void visit(ImageElement element, String value) throws IOException {
068        writeTag(element.toString(), value);
069      }
070    
071      @Override
072      void visitEnclosingElement(ImageElement element) throws IOException {
073        write("<" + element.toString() + ">\n");
074        tagQ.push(element);
075      }
076    
077      @Override
078      void visitEnclosingElement(ImageElement element,
079          ImageElement key, String value)
080           throws IOException {
081        write("<" + element.toString() + " " + key + "=\"" + value +"\">\n");
082        tagQ.push(element);
083      }
084    
085      private void writeTag(String tag, String value) throws IOException {
086        write("<" + tag + ">" + value + "</" + tag + ">\n");
087      }
088    }