Java/File Input Output/File Writer

Append or add some contents to the file

  
 
import java.io.File;
import java.io.FileWriter;
public class Main {
  public static void main(String[] args) throws Exception{
    File file = new File("user.txt");
    FileWriter writer = new FileWriter(file, true);
    writer.write("username=java;password=secret" + System.getProperty("line.separator"));
    writer.flush();
    writer.close();
  }
}

Demonstrate FileWriter.

   
import java.io.FileWriter;
import java.io.IOException;
class FileWriterDemo {
  public static void main(String args[]) throws IOException {
    String source = "test";
    char buffer[] = new char[source.length()];
    source.getChars(0, source.length(), buffer, 0);
    FileWriter f0 = new FileWriter("file1.txt");
    for (int i = 0; i < buffer.length; i += 2) {
      f0.write(buffer[i]);
    }
    f0.close();
    FileWriter f1 = new FileWriter("file2.txt");
    f1.write(buffer);
    f1.close();
    FileWriter f2 = new FileWriter("file3.txt");
    f2.write(buffer, buffer.length - buffer.length / 4, buffer.length / 4);
    f2.close();
  }
}

Implementation of a fast Writer.

 

/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you 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.    
 */
import java.io.IOException;
import java.io.Writer;
/**
 * Implementation of a fast Writer. It was originally taken from JspWriter
 * and modified to have less syncronization going on.
 *
 * @author 
 * @author Anil K. Vijendran
 * @version $Id: VelocityWriter.java 463298 2006-10-12 16:10:32Z henning $
 */
public final class VelocityWriter extends Writer
{
    /**
     * constant indicating that the Writer is not buffering output
     */
    public static final int NO_BUFFER = 0;
    /**
     * constant indicating that the Writer is buffered and is using the
     * implementation default buffer size
     */
    public static final int DEFAULT_BUFFER = -1;
    /**
     * constant indicating that the Writer is buffered and is unbounded;
     * this is used in BodyContent
     */
    public static final int UNBOUNDED_BUFFER = -2;
    private int     bufferSize;
    private boolean autoFlush;
    private Writer writer;
    private char cb[];
    private int nextChar;
    private static int defaultCharBufferSize = 8 * 1024;
    /**
     * Create a buffered character-output stream that uses a default-sized
     * output buffer.
     *
     * @param  writer  Writer to wrap around
     */
    public VelocityWriter(Writer writer)
    {
        this(writer, defaultCharBufferSize, true);
    }
    /**
     * private constructor.
     */
    private VelocityWriter(int bufferSize, boolean autoFlush)
    {
        this.bufferSize = bufferSize;
        this.autoFlush  = autoFlush;
    }
    /**
     * This method returns the size of the buffer used by the JspWriter.
     *
     * @return the size of the buffer in bytes, or 0 is unbuffered.
     */
    public int getBufferSize() { return bufferSize; }
    /**
     * This method indicates whether the JspWriter is autoFlushing.
     *
     * @return if this JspWriter is auto flushing or throwing IOExceptions on
     *         buffer overflow conditions
     */
    public boolean isAutoFlush() { return autoFlush; }
    /**
     * Create a new buffered character-output stream that uses an output
     * buffer of the given size.
     *
     * @param  writer  Writer to wrap around
     * @param  sz     Output-buffer size, a positive integer
     * @param autoFlush
     *
     * @exception  IllegalArgumentException  If sz is <= 0
     */
    public VelocityWriter(Writer writer, int sz, boolean autoFlush)
    {
        this(sz, autoFlush);
        if (sz < 0)
            throw new IllegalArgumentException("Buffer size <= 0");
        this.writer = writer;
        cb = sz == 0 ? null : new char[sz];
        nextChar = 0;
    }
    /**
     * Flush the output buffer to the underlying character stream, without
     * flushing the stream itself.  This method is non-private only so that it
     * may be invoked by PrintStream.
     */
    private final void flushBuffer() throws IOException
    {
        if (bufferSize == 0)
            return;
        if (nextChar == 0)
            return;
        writer.write(cb, 0, nextChar);
        nextChar = 0;
    }
    /**
     * Discard the output buffer.
     */
    public final void clear()
    {
        nextChar = 0;
    }
    private final void bufferOverflow() throws IOException
    {
        throw new IOException("overflow");
    }
    /**
     * Flush the stream.
     * @throws IOException
     *
     */
    public final void flush()  throws IOException
    {
        flushBuffer();
        if (writer != null)
        {
            writer.flush();
        }
    }
    /**
     * Close the stream.
     * @throws IOException
     *
     */
    public final void close() throws IOException {
        if (writer == null)
            return;
        flush();
    }
    /**
     * @return the number of bytes unused in the buffer
     */
    public final int getRemaining()
    {
        return bufferSize - nextChar;
    }
    /**
     * Write a single character.
     * @param c
     * @throws IOException
     *
     */
    public final void write(int c) throws IOException
    {
        if (bufferSize == 0)
        {
            writer.write(c);
        }
        else
        {
            if (nextChar >= bufferSize)
                if (autoFlush)
                    flushBuffer();
                else
                    bufferOverflow();
            cb[nextChar++] = (char) c;
        }
    }
    /**
     * Our own little min method, to avoid loading
     * <code>java.lang.Math</code> if we"ve run out of file
     * descriptors and we"re trying to print a stack trace.
     */
    private final int min(int a, int b)
    {
      return (a < b ? a : b);
    }
    /**
     * Write a portion of an array of characters.
     *
     * <p> Ordinarily this method stores characters from the given array into
     * this stream"s buffer, flushing the buffer to the underlying stream as
     * needed.  If the requested length is at least as large as the buffer,
     * however, then this method will flush the buffer and write the characters
     * directly to the underlying stream.  Thus redundant
     * <code>DiscardableBufferedWriter</code>s will not copy data unnecessarily.
     *
     * @param  cbuf  A character array
     * @param  off   Offset from which to start reading characters
     * @param  len   Number of characters to write
     * @throws IOException
     *
     */
    public final void write(char cbuf[], int off, int len)
        throws IOException
    {
        if (bufferSize == 0)
        {
            writer.write(cbuf, off, len);
            return;
        }
        if (len == 0)
        {
            return;
        }
        if (len >= bufferSize)
        {
            /* If the request length exceeds the size of the output buffer,
            flush the buffer and then write the data directly.  In this
            way buffered streams will cascade harmlessly. */
            if (autoFlush)
                flushBuffer();
            else
                bufferOverflow();
                writer.write(cbuf, off, len);
            return;
        }
        int b = off, t = off + len;
        while (b < t)
        {
            int d = min(bufferSize - nextChar, t - b);
            System.arraycopy(cbuf, b, cb, nextChar, d);
            b += d;
            nextChar += d;
            if (nextChar >= bufferSize)
                if (autoFlush)
                    flushBuffer();
                else
                    bufferOverflow();
        }
    }
    /**
     * Write an array of characters.  This method cannot be inherited from the
     * Writer class because it must suppress I/O exceptions.
     * @param buf
     * @throws IOException
     */
    public final void write(char buf[]) throws IOException
    {
      write(buf, 0, buf.length);
    }
    /**
     * Write a portion of a String.
     *
     * @param  s     String to be written
     * @param  off   Offset from which to start reading characters
     * @param  len   Number of characters to be written
     * @throws IOException
     *
     */
    public final void write(String s, int off, int len) throws IOException
    {
        if (bufferSize == 0)
        {
            writer.write(s, off, len);
            return;
        }
        int b = off, t = off + len;
        while (b < t)
        {
            int d = min(bufferSize - nextChar, t - b);
            s.getChars(b, b + d, cb, nextChar);
            b += d;
            nextChar += d;
            if (nextChar >= bufferSize)
                if (autoFlush)
                    flushBuffer();
                else
                    bufferOverflow();
        }
    }
    /**
     * Write a string.  This method cannot be inherited from the Writer class
     * because it must suppress I/O exceptions.
     * @param s
     * @throws IOException
     */
    public final void write(String s) throws IOException
    {
        if (s != null)
        {
            write(s, 0, s.length());
        }
    }
    /**
     * resets this class so that it can be reused
     * @param writer
     *
     */
    public final void recycle(Writer writer)
    {
        this.writer = writer;
        clear();
    }
}

Use FileWriter to write an array of strings to a file.

  
import java.io.FileWriter;
public class Main {
  public static void main(String[] argv) throws Exception {
    FileWriter fw = new FileWriter("file.dat");
    String strs[] = { "com", "exe", "doc" };
    for (int i = 0; i < strs.length; i++) {
      fw.write(strs[i] + "\n");
    }
    fw.close();
  }
}

Using a Reader and a Writer, returns a String from an InputStream

 

import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.StringWriter;
/* Copyright (c) 1995-2000, The Hypersonic SQL Group.
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 *
 * Redistributions of source code must retain the above copyright notice, this
 * list of conditions and the following disclaimer.
 *
 * Redistributions in binary form must reproduce the above copyright notice,
 * this list of conditions and the following disclaimer in the documentation
 * and/or other materials provided with the distribution.
 *
 * Neither the name of the Hypersonic SQL Group nor the names of its
 * contributors may be used to endorse or promote products derived from this
 * software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED. IN NO EVENT SHALL THE HYPERSONIC SQL GROUP,
 * OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
 * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
 * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 *
 * This software consists of voluntary contributions made by many individuals
 * on behalf of the Hypersonic SQL Group.
 *
 *
 * For work added by the HSQL Development Group:
 *
 * Copyright (c) 2001-2009, The HSQL Development Group
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 *
 * Redistributions of source code must retain the above copyright notice, this
 * list of conditions and the following disclaimer.
 *
 * Redistributions in binary form must reproduce the above copyright notice,
 * this list of conditions and the following disclaimer in the documentation
 * and/or other materials provided with the distribution.
 *
 * Neither the name of the HSQL Development Group nor the names of its
 * contributors may be used to endorse or promote products derived from this
 * software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED. IN NO EVENT SHALL HSQL DEVELOPMENT GROUP, HSQLDB.ORG,
 * OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
 * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
 * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */
/**
 * Collection of static methods for converting strings between different formats
 * and to and from byte arrays.
 * <p>
 * 
 * Includes some methods based on Hypersonic code as indicated.
 * 
 * @author Thomas Mueller (Hypersonic SQL Group)
 * @author Fred Toussi (fredt@users dot sourceforge.net)
 * @version 1.9.0
 * @since 1.7.2
 */
public class Main {
  private static final byte[] HEXBYTES = { (byte) "0", (byte) "1", (byte) "2", (byte) "3",
      (byte) "4", (byte) "5", (byte) "6", (byte) "7", (byte) "8", (byte) "9", (byte) "a",
      (byte) "b", (byte) "c", (byte) "d", (byte) "e", (byte) "f" };

  /**
   * Using a Reader and a Writer, returns a String from an InputStream.
   *
   * Method based on Hypersonic Code
   *
   * @param x InputStream to read from
   * @throws IOException
   * @return a Java string
   */
  public static String inputStreamToString(InputStream x,
          String encoding) throws IOException {
      InputStreamReader in        = new InputStreamReader(x, encoding);
      StringWriter      writer    = new StringWriter();
      int               blocksize = 8 * 1024;
      char[]            buffer    = new char[blocksize];
      for (;;) {
          int read = in.read(buffer);
          if (read == -1) {
              break;
          }
          writer.write(buffer, 0, read);
      }
      writer.close();
      return writer.toString();
  }
}