src/com/google/common/io/AppendableWriter.java

/*
 * Copyright (C) 2006 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.common.io;

import java.io.Closeable;
import java.io.Flushable;
import java.io.Writer;
import java.io.IOException;

/**
 * Writer that places all output on an {@link Appendable} target. If the target
 * is {@link Flushable} or {@link Closeable}, flush()es and close()s will also
 * be delegated to the target.
 *
 * @author Alan Green
 * @author Sebastian Kanthak
 * @since 2009.09.15 <b>tentative</b>
 */
class AppendableWriter extends Writer {
  private final Appendable target;
  private boolean closed;

  /**
   * Creates a new writer that appends everything it writes to {@code target}.
   *
   * @param target target to which to append output
   */
  AppendableWriter(Appendable target) {
    this.target = target;
  }

  /*
   * Abstract methods from Writer
   */

  @Override public void write(char cbuf[], int off, int len)
      throws IOException {
    checkNotClosed();
    // It turns out that creating a new String is usually as fast, or faster
    // than wrapping cbuf in a light-weight CharSequence.
    target.append(new String(cbuf, off, len));
  }

  @Override public void flush() throws IOException {
    checkNotClosed();
    if (target instanceof Flushable) {
      ((Flushable) target).flush();
    }
  }

  @Override public void close() throws IOException {
    this.closed = true;
    if (target instanceof Closeable) {
      ((Closeable) target).close();
    }
  }

  /*
   * Override a few functions for performance reasons to avoid creating
   * unnecessary strings.
   */

  @Override public void write(int c) throws IOException {
    checkNotClosed();
    target.append((char) c);
  }

  @Override public void write(String str) throws IOException {
    checkNotClosed();
    target.append(str);
  }

  @Override public void write(String str, int off, int len) throws IOException {
    checkNotClosed();
    // tricky: append takes start, end pair...
    target.append(str, off, off + len);
  }

  @Override public Writer append(char c) throws IOException {
    checkNotClosed();
    target.append(c);
    return this;
  }

  @Override public Writer append(CharSequence charSeq) throws IOException {
    checkNotClosed();
    target.append(charSeq);
    return this;
  }

  @Override public Writer append(CharSequence charSeq, int start, int end)
      throws IOException {
    checkNotClosed();
    target.append(charSeq, start, end);
    return this;
  }

  private void checkNotClosed() throws IOException {
    if (closed) {
      throw new IOException("Cannot write to a closed writer.");
    }
  }
}