NIO的三大核心配件

channel(通道)

Buffer(缓冲区)

selector(选择器)

案例介绍

读写切换

public static void main(String[] args) {
    //创建一个Buffer，大小为5，可就是可以存放5个int
 IntBuffer intBuffer=IntBuffer.allocate(5);
 for(int i=0;i<intBuffer.capacity();i++){
        intBuffer.put(i*2);
 }
    //读写切换
 intBuffer.flip();
 while(intBuffer.hasRemaining()){
        System.out.println(intBuffer.get());
 }
}

本地方法写

public static void main(String[] args) throws IOException {
 String str="hello";
 //创建一个输出流
 FileOutputStream fileOutputStream=new FileOutputStream("src/test/JAVA/com/hua/nio/a");
 //通过fileOutputStream获取对应的FileChannel，这个FielChannel的真实类型是FileChannelImpl
 FileChannel fileChannel=fileOutputStream.getChannel();
 //创建一个缓冲区ByteBuffer
 ByteBuffer byteBuffer=ByteBuffer.allocate(1024);
 //将str放到byteBuffer
 byteBuffer.put(str.getBytes());
 //对byteBuffer.flip();
 byteBuffer.flip();
 //把byteBuffer的数据写入到fileChannel
 fileChannel.write(byteBuffer);
 fileOutputStream.close();
}

本地方法读

public static void main(String[] args) throws IOException {
    File file=new File("src/test/java/com/hua/nio/a");
 FileInputStream fileInputStream =new FileInputStream(file);
 FileChannel fileChannel=fileInputStream.getChannel();
 ByteBuffer byteBuffer= ByteBuffer.allocate((int)file.length());
 //将通道的数据读入到Buffer
 fileChannel.read(byteBuffer);
 //将byteBuffer的字节数据转成String
 System.out.println(new String(byteBuffer.array()));
 fileInputStream.close();
}

数据的双向交互

public static void main(String[] args) throws IOException {
    FileInputStream fileInputStream=new FileInputStream("src/test/java/com/hua/nio/a");
 FileOutputStream fileOutputStream=new FileOutputStream("src/test/java/com/hua/nio/b");
 FileChannel fileChannel1=fileInputStream.getChannel();
 FileChannel fileChannel2=fileOutputStream.getChannel();
 ByteBuffer byteBuffer= ByteBuffer.allocate(512);
 while(true){
        //必须要clear，当下面fileChannel2的write的时候,此时的position会从0开始到limit，如果不clear回归到原来，
 //当position和limit相等的时候，fileChannel1.read的返回结果为-1
 byteBuffer.clear();
 int read=fileChannel1.read(byteBuffer);
 System.out.println(read);
 if(read == -1){
            break;
 }
        byteBuffer.flip();
 fileChannel2.write(byteBuffer);
 }
    fileInputStream.close();
 fileOutputStream.close();
}

通道的数据转换

public static void main(String[] args) throws IOException {
    FileInputStream fileInputStream =new FileInputStream("src/test/java/com/hua/nio/a");
 FileOutputStream fileOutputStream=new FileOutputStream("src/test/java/com/hua/nio/c");
 FileChannel fileChannel1=fileInputStream.getChannel();
 FileChannel fileChannel2=fileOutputStream.getChannel();
 fileChannel2.transferFrom(fileChannel1,0,fileChannel1.size());
 fileChannel1.close();
 fileChannel2.close();
 fileInputStream.close();
 fileOutputStream.close();
}

类型的buffer

public static void main(String[] args) {
    ByteBuffer buffer= ByteBuffer.allocate(64);
 buffer.putInt(100);
 buffer.putLong(5);
 buffer.putChar('天');
 buffer.putShort((short)11);
 buffer.flip();
 System.out.println();
 System.out.println(buffer.getInt());
 System.out.println(buffer.getLong());
 System.out.println(buffer.getChar());
 System.out.println(buffer.getShort());
}

只读的buffer

public static void main(String[] args) {
    ByteBuffer buffer= ByteBuffer.allocate(64);
 for(int i=0;i<64;i++){
        buffer.put((byte)i);
 }
    buffer.flip();
 //设置byteBuffer是只读的
 ByteBuffer readOnlyBuffer=buffer.asReadOnlyBuffer();
 System.out.println(readOnlyBuffer.getClass());
 while(readOnlyBuffer.hasRemaining()){
        System.out.println(readOnlyBuffer.get());
 }
}

内存上的修改

public static void main(String[] args) throws IOException {
    RandomaccessFile randomAccessFile=new RandomAccessFile("src/test/java/com/hua/nio/a","rw");
 FileChannel channel=randomAccessFile.getChannel();
 //FileChannel.MapMode.READ_WRITR使用的是读写模式
 //第一个参数表示直接修改的起始位置
 //第二个参数表示映射到内存的大小
 //也就是说我们只能修改0到4的索引位置，
 MAppedByteBuffer mappedByteBuffer=channel.map(FileChannel.MapMode.READ_WRITE,0,5);
 mappedByteBuffer.put(0,(byte)'H');
 mappedByteBuffer.put(2,(byte)'L');
 randomAccessFile.close();
}