JavaNIO之缓冲区(Buffers)

下面的例子来自于《Java I/O,NIO and NIO2》，阅读本书Buffers之后所作的代码笔记。

例1：Buffer的几个重要属性及修改

package chapter06;

import java.nio.Buffer;
import java.nio.ByteBuffer;

/**
* Buffer的几个重要属性及修改
*/
public class BufferDemo01 {
public static void main(String[] args) {
//分配容量为7的字节缓冲区
Buffer buffer = ByteBuffer.allocate(7);
System.out.println("Capacity: " + buffer.capacity());
System.out.println("Limit: " + buffer.limit());
System.out.println("Position: " + buffer.position());
System.out.println("Remaining: " + buffer.remaining());
System.out.println("Changing buffer limit to 5");
//修改属性limit
buffer.limit(5);
System.out.println("Limit: " + buffer.limit());
System.out.println("Position: " + buffer.position());
System.out.println("Remaining: " + buffer.remaining());
System.out.println("Changing buffer position to 3");
//修改属性position
buffer.position(3);
System.out.println("Position: " + buffer.position());
System.out.println("Remaining: " + buffer.remaining());
System.out.println(buffer);
}
}

运行结果：

Capacity: 7

Limit: 7

Position: 0

Remaining: 7

Changing buffer limit to 5

Limit: 5

Position: 0

Remaining: 5

Changing buffer position to 3

Position: 3

Remaining: 2

java.nio.HeapByteBuffer[pos=3 lim=5 cap=7]

例2：通过分配空间和包装的方式创建字节缓冲区

package chapter06;

import java.nio.ByteBuffer;

/**
* 通过分配空间和包装的方式创建字节缓冲区
*/
public class BufferDemo02 {
public static void main(String[] args) {
//分配空间的方式
ByteBuffer buffer1 = ByteBuffer.allocate(10);
if (buffer1.hasArray()) {
System.out.println("buffer1 array: " + buffer1.array());
System.out.println("Buffer1 array offset: " + buffer1.arrayOffset());
System.out.println("Capacity: " + buffer1.capacity());
System.out.println("Limit: " + buffer1.limit());
System.out.println("Position: " + buffer1.position());
System.out.println("Remaining: " + buffer1.remaining());
System.out.println();
}

//通过包装的方式创建字节缓冲区
byte[] bytes = new byte[200];
ByteBuffer buffer2 = ByteBuffer.wrap(bytes);
buffer2 = ByteBuffer.wrap(bytes, 10, 50);
if (buffer2.hasArray()) {
System.out.println("buffer2 array: " + buffer2.array());
System.out.println("Buffer2 array offset: " + buffer2.arrayOffset());
System.out.println("Capacity: " + buffer2.capacity());
System.out.println("Limit: " + buffer2.limit());
System.out.println("Position: " + buffer2.position());
System.out.println("Remaining: " + buffer2.remaining());
}
}
}

运行结果：

buffer1 array: [B@484b61fc

Buffer1 array offset: 0

Capacity: 10

Limit: 10

Position: 0

Remaining: 10

buffer2 array: [B@45fe3ee3

Buffer2 array offset: 0

Capacity: 200

Limit: 60

Position: 10

Remaining: 50

例3：读写字节缓冲区

package chapter06;

import java.nio.ByteBuffer;

/**
* 读写字节缓冲区
*/
public class BufferDemo03 {
public static void main(String[] args) {
ByteBuffer buffer = ByteBuffer.allocate(7);
//初始时打印四个属性
System.out.println("Capacity = " + buffer.capacity());
System.out.println("Limit = " + buffer.limit());
System.out.println("Position = " + buffer.position());
System.out.println("Remaining = " + buffer.remaining());
//向字节缓冲区中添加数据
buffer.put((byte) 10).put((byte) 20).put((byte) 30);
//添加内容后再打印这四个属性
System.out.println("Capacity = " + buffer.capacity());
System.out.println("Limit = " + buffer.limit());
System.out.println("Position = " + buffer.position());
System.out.println("Remaining = " + buffer.remaining());
for (int i = 0; i < buffer.position(); i++)
System.out.println(buffer.get(i));
}
}

运行结果：

Capacity = 7

Limit = 7

Position = 0

Remaining = 7

Capacity = 7

Limit = 7

Position = 3

Remaining = 4

10

20

30

例4：读写字符缓冲区

package chapter06;

import java.nio.CharBuffer;

/**
* 读写字符缓冲区
*/
public class BufferDemo04 {
public static void main(String[] args) {
String[] poem = { "Roses are red", "Violets are blue",
"Sugar is sweet", "And so are you." };
//字符缓冲区
CharBuffer buffer = CharBuffer.allocate(50);
for (int i = 0; i < poem.length; i++) {
//填充缓冲区
for (int j = 0; j < poem[i].length(); j++)
buffer.put(poem[i].charAt(j));
//执行翻转操作,从读变为写状态
buffer.flip();
//冲缓冲区中读取数据
while (buffer.hasRemaining())
System.out.print(buffer.get());
//清空缓冲区,方便下次填充
buffer.clear();
System.out.println();
}
}
}

运行结果：

Roses are red

Violets are blue

Sugar is sweet

And so are you.

例5：标记当前缓冲区的位置,然后重置当前位置到标记的位置

package chapter06;

import java.nio.ByteBuffer;

/**
* 标记当前缓冲区的位置,然后重置当前位置到标记的位置
*/
public class BufferDemo05 {
public static void main(String[] args) {
ByteBuffer buffer = ByteBuffer.allocate(7);
//填充缓冲区
buffer.put((byte) 10).put((byte) 20).put((byte) 30).put((byte) 40);
//设置limit属性
buffer.limit(4);
//将position为1的地方做标记
buffer.position(1).mark().position(3);
//这里从position为3的地方取数据
System.out.println(buffer.get());
System.out.println();
//重置,把当前position的值设置回1
buffer.reset();
//从position为1的位置重新开始读数据
while (buffer.hasRemaining())
System.out.println(buffer.get());
}
}

运行结果：

40

20

30

40