java.nio.Buffer分析

在研究Apache Mina源代码时，在IoFilter中使用IoBuffer做为数据缓冲对象，而IoBuffer的实现来自于java.nio.Buffer。Buffer中的flip()、clear()、reset()、mark()等概念让我有点糊涂，仔细看了jdk的文档说明，才对Buffer对象的概念了然于胸。 在Buffer类当中有以下四个重要的属性： mark：标记位，用于reset（）时把position恢复到原来的位置，调用mark（）方法使position的值赋与mark position：表示Buffer中第一个可以被读取或写入的数据的位置，每次调用put（）方法时,把写入的数据放到position位置，然后position的值就会加1 limit：表示buffer中第一个不可被读取或写入的数据的位置，也即停止位，数据操作到此为止 capacity：初始化时调用allocate(int size)为buffer分配的空间大小，不可变 演示代码如下： view plaincopy to clipboardprint? import java.nio.ByteBuffer; public class ByteBufferTest { public static void main(String[] args) { ByteBuffer bb=ByteBuffer.allocate(10); for(int i=1;i<9;i++){ bb.put((byte)i); } System.out.println("pos:"+bb.position()); System.out.println("limit:"+bb.limit()); System.out.println("cap:"+bb.capacity()); bb.flip(); System.out.println("/nafter flip"); System.out.println("pos:"+bb.position()); System.out.println("limit:"+bb.limit()); System.out.println("cap:"+bb.capacity()); bb.mark(); System.out.println("/nafter mark"); System.out.println("pos:"+bb.position()); System.out.println("limit:"+bb.limit()); System.out.println("cap:"+bb.capacity()); bb.reset(); System.out.println("/nafter reset"); System.out.println("pos:"+bb.position()); System.out.println("limit:"+bb.limit()); System.out.println("cap:"+bb.capacity()); bb.clear(); System.out.println("/nafter clear"); System.out.println("pos:"+bb.position()); System.out.println("limit:"+bb.limit()); System.out.println("cap:"+bb.capacity()); bb.limit(1); bb.put((byte)9); bb.put((byte)10);//超出limit范围，抛出java.nio.BufferOverflowException异常 bb.put((byte)11); } } import java.nio.ByteBuffer; public class ByteBufferTest { public static void main(String[] args) { ByteBuffer bb=ByteBuffer.allocate(10); for(int i=1;i<9;i++){ bb.put((byte)i); } System.out.println("pos:"+bb.position()); System.out.println("limit:"+bb.limit()); System.out.println("cap:"+bb.capacity()); bb.flip(); System.out.println("/nafter flip"); System.out.println("pos:"+bb.position()); System.out.println("limit:"+bb.limit()); System.out.println("cap:"+bb.capacity()); bb.mark(); System.out.println("/nafter mark"); System.out.println("pos:"+bb.position()); System.out.println("limit:"+bb.limit()); System.out.println("cap:"+bb.capacity()); bb.reset(); System.out.println("/nafter reset"); System.out.println("pos:"+bb.position()); System.out.println("limit:"+bb.limit()); System.out.println("cap:"+bb.capacity()); bb.clear(); System.out.println("/nafter clear"); System.out.println("pos:"+bb.position()); System.out.println("limit:"+bb.limit()); System.out.println("cap:"+bb.capacity()); bb.limit(1); bb.put((byte)9); bb.put((byte)10);//超出limit范围，抛出java.nio.BufferOverflowException异常 bb.put((byte)11); } } 输出结果： view plaincopy to clipboardprint? pos:8 limit:10 cap:10 after flip pos:0 limit:8 cap:10 after mark pos:0 limit:8 cap:10 after reset pos:0 limit:8 cap:10 after clear pos:0 limit:10 cap:10 Exception in thread "main" java.nio.BufferOverflowException at java.nio.Buffer.nextPutIndex(Buffer.java:419) at java.nio.HeapByteBuffer.put(HeapByteBuffer.java:145) at com.gftech.mytool.mina.ByteBufferTest.main(ByteBufferTest.java:45)