spring-core io包DataBuffer，PoolDataBuffer，DataBufferFactory接口源码解析

一、接口继承图

二、接口类功能概述和实现

DataBuffer是对java NIO中的ByteBuffer 和Netty的ByteBuf 的统一包装，包含对字节缓冲区操作的各种方法，如下：

      

      DefaultDataBuffer是DataBuffer的默认实现，基于java NIO的ByteBuffer实现， 相关ByteBuffer的操作参考：

       https://blog.csdn.net/shuaiAWP/article/details/51915983

      PooledDataBuffer继承DataBuffer接口，增加了引用计数的方法，保留方法将引用计数增加1。 释放方法将计数减1，并在计数达到0时释放缓冲区的内存，增加的方法如下：

     

    NettyDataBuffer是PooledDataBuffer的唯一实现，基于Netty 的ByteBuf实现。

    DataBufferFactory接口提供了用于构造DataBuffer的方法，如下所示：

  

其中join方法用于将多个DataBuffer做合并处理。DefaultDataBufferFactory是DefaultDataBuffer的工厂类，NettyDataBufferFactory是NettyDataBuffer的工厂类。

DataBufferUtils是DataBuffer接口的工具类，它包含从InputStream或NIO通道读取DataBuffer对象的Flux的方法，以及将数据缓冲区Flux写入OutputStream或Channel的方法等。但是该工具类是基于反应式编程框架Reactor中的Flux元素写的，Reactor参考如下：https://www.ibm.com/developerworks/cn/java/j-cn-with-reactor-response-encode/index.html?lnk=hmhm

参考测试用例如下：

@Test
public void writeAndRead() throws Exception{
	DataBufferFactory dataBufferFactory=new DefaultDataBufferFactory();
	DataBuffer buffer = dataBufferFactory.allocateBuffer(2);
	buffer.write(new byte[]{'a', 'b', 'c'});
	System.out.println("capacity-->"+buffer.capacity());
	System.out.println("readPosition-->"+buffer.readPosition());
	System.out.println("writePosition-->"+buffer.writePosition());
	System.out.println("writableByteCount-->"+buffer.writableByteCount());
	System.out.println("readableByteCount-->"+buffer.readableByteCount());

	int index=buffer.indexOf(p -> p=='c', 1);
	System.out.println("index-->"+index);

	int ch = buffer.read();
	assertEquals('a', ch);

	buffer.readPosition(2);
	ch = buffer.read();
	assertEquals('c', ch);

	buffer.write((byte) 'd');
	buffer.write((byte) 'e');

	byte[] result = new byte[2];
	buffer.read(result);

	assertArrayEquals(new byte[]{'d', 'e'}, result);

	ByteBuffer buffer2=ByteBuffer.allocate(4);
	buffer2.put((byte) '1');
	buffer2.put((byte) '2');
	buffer2.put((byte) '3');
	buffer2.put((byte) '4');
	buffer2.position(2);
	System.out.println("write before writePosition-->"+buffer.writePosition());
	buffer.write(buffer2);
	System.out.println("write after writePosition-->"+buffer.writePosition());

	ByteBuffer buffer3=buffer.asByteBuffer(4, 5);
	ch = buffer3.get();
	assertEquals('e', ch);
	assertEquals(5,buffer3.limit());

	InputStream in=buffer.asInputStream();
	in.read(result);
	assertArrayEquals(new byte[]{'3', '4'}, result);

	DataBufferUtils.release(buffer);
}

@Test
public void retainAndRelease() {
	NettyDataBufferFactory dataBufferFactory=new NettyDataBufferFactory(new PooledByteBufAllocator());
	PooledDataBuffer buffer = dataBufferFactory.allocateBuffer(4);
//		buffer.write((byte) 'a');

	buffer.retain();
	boolean result = buffer.release();
	assertFalse(result);
	result = buffer.release();
	assertTrue(result);
}