buffer状态位分析

buffer分片示例

src/main/java/com/llthunder/netty/nio/buffer/BufferDemo.java

+package com.llthunder.netty.nio.buffer;
+
+import com.sun.org.apache.bcel.internal.util.ClassPath;
+
+import java.io.*;
+import java.nio.Buffer;
+import java.nio.ByteBuffer;
+import java.nio.channels.FileChannel;
+
+/**
+ * buffer基本示例:演示position/limit/capacity的变化
+ */
+public class BufferDemo {
+
+    public static void main(String[] args) throws IOException {
+        //读取文件流，此处操作时I/O操作
+        String fileUrl = BufferDemo.class.getClassLoader().getResource("BufferDemoText.text").getFile();
+        FileInputStream inputStream = new FileInputStream(fileUrl);
+        FileChannel inputChannel = inputStream.getChannel();
+        //创建一个大小为10的缓冲区
+        ByteBuffer byteBuffer = ByteBuffer.allocate(100);
+        out("初始化", byteBuffer);
+        //将数据写入缓冲区
+        inputChannel.read(byteBuffer);
+        out("调用read", byteBuffer);
+        //锁定写入范围
+        byteBuffer.flip();
+        out("调用flip", byteBuffer);
+        while (byteBuffer.hasRemaining()){
+            byte b = byteBuffer.get();
+        }
+        //可以理解对flip的解锁
+        byteBuffer.clear();
+        out("调用clear", byteBuffer);
+        //关闭流
+        inputChannel.close();
+        inputStream.close();
+    }
+
+    public static void out(String step, Buffer buffer){
+        System.out.println(step + ":");
+        System.out.print("position:" + buffer.position() + ",");
+        System.out.print("limit:" + buffer.limit() + ",");
+        System.out.print("capacity:" + buffer.capacity() + ",");
+        System.out.println();System.out.println();
+    }
+}

src/main/java/com/llthunder/netty/nio/buffer/BufferSliceDemo.java

+package com.llthunder.netty.nio.buffer;
+
+import java.nio.IntBuffer;
+
+/**
+ * 缓冲区分片
+ */
+public class BufferSliceDemo {
+
+    public static void main(String[] args) {
+        IntBuffer intBuffer = IntBuffer.allocate(10);
+        //给缓冲区的数据复制：1-10
+        for(int i = 1; i <= intBuffer.capacity(); i++){
+            intBuffer.put(i);
+        }
+        //分片：创建子缓冲区
+        intBuffer.position(3);
+        intBuffer.limit(7);
+        IntBuffer slice = intBuffer.slice();
+        //给子缓冲区中的数据*10
+        for (int i = 0; i < slice.capacity(); i++){
+            int value = slice.get(i);
+            slice.put(i, value  * 10);
+        }
+        //重置主buffer的状态位
+        intBuffer.position(0);
+        intBuffer.limit(intBuffer.capacity());
+        //读取buffer中的数据
+        while (intBuffer.hasRemaining()){
+            System.out.print(intBuffer.get() + "    ");
+        }
+    }
+}

src/main/java/com/llthunder/netty/nio/buffer/IntbufferDemo.java → src/main/java/com/llthunder/netty/nio/buffer/IntBufferDemo.java

@@ -2,7 +2,10 @@ package com.llthunder.netty.nio.buffer;
 
 import java.nio.IntBuffer;
 
-public class IntbufferDemo {
+/**
+ * buffer操作基本API示例
+ */
+public class IntBufferDemo {
 
     public static void main(String[] args) {
         //buffer中共有3个属性
@@ -20,7 +23,7 @@ public class IntbufferDemo {
         while (intBuffer.hasRemaining()){
             //读取缓冲区当前position位置的数据，知道position=limit
             int j = intBuffer.get();
-            System.out.println(j);
+            System.out.print(j + "   ");
         }
     }
 }

src/main/resources/BufferDemoText.text

+buffer基本示例:演示position/limit/capacity的变化
\ No newline at end of file