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()); //
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
->
->
->
->
->
->
->
->
Int Buffer
->
->
Char Buffer
->
->
->
-> 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();
}
}