EscapingWriter.java

/*
 * Copyright 2009 Google Inc.
 * 
 * Licensed under the Apache License, Version 2.0 (the "License"); you may not
 * use this file except in compliance with the License. You may obtain a copy of
 * the License at
 * 
 * http://www.apache.org/licenses/LICENSE-2.0
 * 
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
 * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
 * License for the specific language governing permissions and limitations under
 * the License.
 */
package com.google.jstestdriver.token;

import com.google.common.collect.Maps;

import java.io.FilterWriter;
import java.io.IOException;
import java.io.Writer;
import java.util.Collections;
import java.util.Map;

/**
 * Automatically escapes \, ', ", \n, \f, \r when writing to the underlying writer.
 * (Why isn't the Gson Escaper public? Arg!)
 * Not Thread Safe!
 * @author corysmith@google.com (Cory Smith)
 *
 */
public class EscapingWriter extends FilterWriter {

  private static final Map<Character, char[]> REPLACE;
  static {
    Map<Character, char[]> replace = Maps.newHashMap();
    replace.put('\\', new char[]{'\\','\\'});
    replace.put('\n', new char[]{'\\','n'});
    replace.put('\r', new char[]{'\\','r'});
    replace.put('\f', new char[]{'\\','f'});
    replace.put('\'', new char[]{'\\','\''});
    replace.put('"', new char[]{'\\','"'});
    REPLACE = Collections.unmodifiableMap(replace);
  }
  
  private final char[] escapedBuffer = new char[256]; 
  
  public EscapingWriter(Writer out) {
    super(out);
  }
  
  @Override
  public void write(char[] cbuf, int off, int len) throws IOException {
    int pos = 0;
    for (int i = off; i < len; i++ ) {
      if (REPLACE.containsKey(Character.valueOf(cbuf[i]))) {
        pos = writeToBuffer(pos, REPLACE.get(cbuf[i]));
      } else {
        pos = writeToBuffer(pos, cbuf[i]);
      }
    }
    out.write(escapedBuffer, 0, pos);
  }

  private int writeToBuffer(int pos, char c)  throws IOException {
    if (pos + 1 > escapedBuffer.length) { // flush it
      out.write(escapedBuffer, 0, pos);
      pos = 0;
    }
    escapedBuffer[pos++] = c;
    return pos;
  }

  private int writeToBuffer(int pos, char[] characters) throws IOException {
    if (pos + characters.length > escapedBuffer.length) { // flush it
      out.write(escapedBuffer, 0, pos);
      pos = 0;
    }

    System.arraycopy(characters, 0, escapedBuffer, 0, pos);
    pos += characters.length;
    return pos;
  }

  @Override
  public void write(int c) throws IOException {
    Character chr = Character.valueOf((char)c);
    if (REPLACE.containsKey(chr)) {
      out.write(REPLACE.get(chr));
    } else {
      out.write(c);
    }
  }
  
  @Override
  public void write(char[] cbuf) throws IOException {
    write(cbuf, 0, cbuf.length);
  }
}