Created
September 11, 2017 04:27
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Netty ByteBuf Example
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| package netty.toturials; | |
| import io.netty.buffer.ByteBuf; | |
| import io.netty.buffer.Unpooled; | |
| import io.netty.util.ByteProcessor; | |
| /** | |
| * 1. ByteBuf根据其分配空间不同有可以分为三种：JVM堆内的，直接内存，组合的。堆内受JVM的管辖，使用上相对安全一些，但是要注意GC是会影响性能。 | |
| * 直接内存不受JVM的管控，在编程的时候要注意不用的ByteBuf要手动释放，否则会造成内存泄漏。 | |
| * <p> | |
| * 2. ByteBuf的创建： | |
| * a. Pooled | |
| * b. Unpooled | |
| * c. channel.alloc() | |
| * <p> | |
| * 3. ByteBuf的内部可以分成三个部分：可读的，可写的，可丢弃的。 | |
| * 可读空间由read index标记，可写空间由write index标记，可丢弃是已经读过的字节。 | |
| * <p> | |
| * 4. markReaderIndex可以对当前的reader index打一个标记，后续如果还有读操作，调用resetReaderIndex可以把readerIndex重置到原来的位置。 | |
| * <p> | |
| * 5. discardReadByte可以把读过的空间释放，这时buffer的可写空间和writerIndex会相应的改变。discardReadBytes在内存紧张的时候有用，但是 | |
| * 调用该方法会伴随buffer的内存整理的． | |
| * <p> | |
| * 6. buffer的派生操作，派生操作會产生一个新的byte buffer。这里的新指得是byte buf的引用是新的所有的index也是新的。但是他们共用一套存储。 | |
| * duplicate，slice，order，readSlice | |
| * <p> | |
| * 7. 通过hasArray检查一个ByteBuf heap based还是direct buffer | |
| * <p> | |
| * 8. 如果想要复制一个ByteBuffer请使用copy | |
| * <p> | |
| * 9. clear vs discardReadBytes。clear是把readerIndex和writerIndex重置到0，这时writable capacity恢复到原始值。 | |
| * discardReadBytes只是把读过的字节丢弃，并进行一次内存整理。 | |
| * <p> | |
| * 10. 引用计数。引用计数记录了当前byteBuf被引用的次数。当refCnt == 0时，这个ByteBuf即可被release。 | |
| */ | |
| public class ByteBufExample { | |
| public static void main(String[] args) { | |
| ByteBuf buffer = Unpooled.buffer(0, 1024 * 1024); | |
| for (int i = 0; i < 256 * 1024; i++) { | |
| buffer.writeInt(i); | |
| } | |
| // 一个int占四个字节，所以1M最对能放256 × 1024个数字 | |
| assert 0 == buffer.writableBytes(); | |
| assert 1024 * 1024 == buffer.capacity(); | |
| assert 1024 * 1024 == buffer.readableBytes(); | |
| buffer.readBytes(20); | |
| assert 20 == buffer.readerIndex(); | |
| buffer.markReaderIndex(); | |
| buffer.readBytes(20); | |
| assert 40 == buffer.readerIndex(); | |
| buffer.resetReaderIndex(); | |
| assert 20 == buffer.readerIndex(); | |
| buffer.discardReadBytes(); | |
| assert 20 == buffer.writableBytes(); | |
| ByteBuf buffer1 = Unpooled.buffer(0, 1024 * 1024);//heap buffer | |
| ByteBuf buffer2 = Unpooled.directBuffer(0, 1024 * 1024);//direct buffer | |
| assert buffer1.hasArray(); | |
| assert !buffer2.hasArray(); | |
| ByteBuf buffer3 = Unpooled.buffer(0, 1024); | |
| ByteBuf buffer4 = buffer3.duplicate(); | |
| buffer3.writeInt(1); | |
| assert 4 == buffer3.writerIndex(); | |
| assert 0 == buffer4.writerIndex(); | |
| assert 1 == buffer4.array()[3]; | |
| buffer3.readInt(); | |
| assert 4 == buffer3.readerIndex(); | |
| assert 0 == buffer4.readerIndex(); | |
| buffer3.discardReadBytes(); | |
| assert 0 == buffer3.readerIndex(); | |
| assert 0 == buffer3.readerIndex(); | |
| ByteBuf buffer5 = Unpooled.buffer(); | |
| assert 1 == buffer5.refCnt(); | |
| ByteBuf retainedBuffer = buffer5.retain(); | |
| assert 2 == retainedBuffer.refCnt(); | |
| assert retainedBuffer.release(2); | |
| ByteBuf buffer6 = Unpooled.buffer(0, 20);//heap buffer | |
| buffer6.writeInt(5).writeInt(5).writeInt(5).writeInt(5).writeInt(5); | |
| buffer6.readInt(); | |
| assert 4 == buffer6.readerIndex(); | |
| assert 20 == buffer6.writerIndex(); | |
| assert 0 == buffer6.writableBytes(); | |
| ByteBuf buffer7 = Unpooled.buffer(); | |
| buffer7.writeBytes("123\rasdf\r\n".getBytes()); | |
| int i = buffer7.forEachByte(ByteProcessor.FIND_CR); | |
| assert 3 == i; | |
| ByteBuf buffer8 = Unpooled.buffer(0, 20);//heap buffer | |
| buffer8.writeInt(5).writeInt(5).writeInt(5).writeInt(5).writeInt(5); | |
| buffer8.clear(); | |
| assert 0 == buffer8.readerIndex(); | |
| assert 0 == buffer8.writerIndex(); | |
| assert 20 == buffer8.writableBytes(); | |
| assert 20 == buffer8.capacity(); | |
| } | |
| } |
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