java基础---->java中nio的使用（一）

　　JDK 1.4 中引入的新输入输出 (NIO) 库在标准 Java 代码中提供了高速的、面向块的 I/O。今天我们就简单的学习一下nio的知识。我笑，便面如春花，定是能感动人的，任他是谁。

nio的简单使用

FileInputStream、FileOutputStream和RandomAccessFile用于产生FileChannel。这些字节操纵流，与底层的nio特性一致。

一、FileChannel的产生

public void nioTest_1() {
    final int BUFFER_SIZE = 1024;
    try {
        // 向文件里面写入数据
        FileChannel fc = new FileOutputStream("file/linux.txt").getChannel();
        fc.write(ByteBuffer.wrap("I love you".getBytes()));
        fc.close();

        // 向文件里面追加数据
        fc = new RandomAccessFile("file/linux.txt", "rw").getChannel();
        System.out.println(fc.position()); // 0
        fc.position(fc.size());
        fc.write(ByteBuffer.wrap(", china.".getBytes()));
        fc.close();

        // 向文件里面读取数据
        fc = new FileInputStream("file/linux.txt").getChannel();
        ByteBuffer buffer = ByteBuffer.allocate(BUFFER_SIZE);
        fc.read(buffer);
        buffer.flip();
        while (buffer.hasRemaining()) {
            System.out.print((char) buffer.get()); // I love you, china.
        }
    } catch (Exception e) {
        e.printStackTrace();
    }
}

二、文件的复制功能

public void nioTest_2() {
    final int BUFFER_SIZE = 1024;
    try {
        FileChannel out = new FileOutputStream("file/huhx.txt").getChannel();
        FileChannel in = new FileInputStream("file/linux.txt").getChannel();
        ByteBuffer buffer = ByteBuffer.allocate(BUFFER_SIZE);

        while (in.read(buffer) != -1) {
            buffer.flip(); // 准备写数据
            out.write(buffer);
            buffer.clear(); // 准备读数据
        }
        out.close();
        in.close();
    } catch (Exception e) {
        e.printStackTrace();
    }
}

关于文件的复制，jdk提供了一个简单的方法实现。

public void nioTest_3() {
    final int BUFFER_SIZE = 1024;
    try {
        FileChannel out = new FileOutputStream("file/huhx.txt").getChannel();
        FileChannel in = new FileInputStream("file/linux.txt").getChannel();
        ByteBuffer buffer = ByteBuffer.allocate(BUFFER_SIZE);

        in.transferTo(0, in.size(), out);
//            out.transferFrom(in, 0, in.size());  这个和上述实现的目标是一样的。
    } catch (Exception e) {
        e.printStackTrace();
    }
}

三、buffer之间的转换

public void nioTest_4() {
    ByteBuffer buffer = ByteBuffer.wrap(new byte[]{0, 0, 0, 0, 0, 0, 0, 'a'});
    buffer.rewind();
    System.out.println("Byte Buffer");
    while (buffer.hasRemaining()) {
        System.out.println(buffer.position() + " -> " + buffer.get());
    }

    IntBuffer intBuffer = ((ByteBuffer) buffer.rewind()).asIntBuffer();
    System.out.println("Int Buffer");
    while (intBuffer.hasRemaining()) {
        System.out.println(intBuffer.position() + " -> " + intBuffer.get());
    }

    CharBuffer charBuffer = ((ByteBuffer) buffer.rewind()).asCharBuffer();
    System.out.println("Char Buffer");
    while (charBuffer.hasRemaining()) {
        System.out.println(charBuffer.position() + " -> " + charBuffer.get());
    }
}

运行的效果：

Byte Buffer
0 -> 0
1 -> 0
2 -> 0
3 -> 0
4 -> 0
5 -> 0
6 -> 0
7 -> 97
Int Buffer
0 -> 0
1 -> 97
Char Buffer
0 ->  
1 ->  
2 ->  
3 -> a

四、存储器映射文件

public void nioTest_6() {
    final int length = 0x8FFFFFF;
    try {
        MappedByteBuffer out = new RandomAccessFile("file/huhx.txt", "rw").getChannel().map(FileChannel.MapMode.READ_WRITE, 0, length);
        for (int i = 0; i < length; i++) {
            out.put((byte) 'x');
        }
        System.out.println("Finishing writing");
        for (int i = length / 2; i < length / 2 + 6; i++) {
            System.out.print((char) out.get(i));
        }
    } catch (Exception e) {
        e.printStackTrace();
    }
}

五、文件加锁

public void nioTest_7() {
    try {
        FileOutputStream fos = new FileOutputStream("file/huhx.txt", false);
        FileLock fileLock = fos.getChannel().tryLock();
        if (fileLock != null) {
            System.out.println("Locked File");
            Thread.sleep(1000);
            fos.write("hello world".getBytes());
            fileLock.release();
            System.out.println("Released Lock");
        }
        fos.close();
    } catch (Exception e) {
        e.printStackTrace();
    }
}

 友情链接

• nio的基础概念及使用： http://blog.csdn.net/qq_21430549/article/details/52145008
• 比较详细的nio说明：    http://blog.csdn.net/tzs_1041218129/article/details/54917857