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‎JdkLearn/src/main/java/com/learnjava/io/nio/MappedByteBufferTest.java‎
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‎JdkLearn/src/main/java/com/learnjava/io/nio/MappedByteBufferTest.java‎
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‎note/Netty/零拷贝.md‎
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+14-1Lines changed: 14 additions & 1 deletion
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@@ -1,5 +1,8 @@
 package com.learnjava.io.nio;
 
+import java.io.FileInputStream;
+import java.io.FileOutputStream;
+import java.io.IOException;
 import java.io.RandomAccessFile;
 import java.nio.MappedByteBuffer;
 import java.nio.channels.FileChannel;
@@ -17,13 +20,55 @@ public static void main(String[] args) throws Exception {
 
         MappedByteBuffer mappedByteBuffer = channel.map(FileChannel.MapMode.READ_WRITE, 0, 5);
 
-        mappedByteBuffer.put(0, (byte)'H');
-        mappedByteBuffer.put(3, (byte)'9');
+        mappedByteBuffer.put(0, (byte) 'H');
+        mappedByteBuffer.put(3, (byte) '9');
 
         // IndexOutOfBoundsException
-        mappedByteBuffer.put(5, (byte)'Y');
+        mappedByteBuffer.put(5, (byte) 'Y');
 
         randomAccessFile.close();
         System.out.println("change success");
     }
+
+    /**
+     *
+     * @param from
+     * @param to
+     * @throws IOException
+     */
+    public static void mmap4zeroCopy(String from, String to) throws IOException {
+        FileChannel source = null;
+        FileChannel destination = null;
+        try {
+            source = new RandomAccessFile(from, "r").getChannel();
+            destination = new RandomAccessFile(to, "rw").getChannel();
+            MappedByteBuffer inMappedBuf =
+                    source.map(FileChannel.MapMode.READ_ONLY, 0, source.size());
+            destination.write(inMappedBuf);
+        } finally {
+            if (source != null) {
+                source.close();
+            }
+            if (destination != null) {
+                destination.close();
+            }
+        }
+    }
+
+    public static void sendfile4zeroCopy(String from, String to) throws IOException{
+        FileChannel source = null;
+        FileChannel destination = null;
+        try {
+            source = new FileInputStream(from).getChannel();
+            destination = new FileOutputStream(to).getChannel();
+            source.transferTo(0, source.size(), destination);
+        } finally {
+            if (source != null) {
+                source.close();
+            }
+            if (destination != null) {
+                destination.close();
+            }
+        }
+    }
 }
@@ -4,7 +4,20 @@
 
 ## 正文
 
-### 1. mmap和sendFile零拷贝
+### 1. 再看IO
+
+在深入零拷贝机制之前，先来了解下传统BIO通信底层发生了什么，为什么会这么“消耗资源”。Linux服务器是现在绝大多数系统的首选，它的优点就不再赘述，下面的分析都基于Linux环境来进行。作为一台服务器，最常见的功能就是
+获取客户端发送过来的请求，然后再去查数据库DB获取到想要的数据，再将数据以一定的业务逻辑处理后传回给客户端，这一过程主要会调用Linux内核的以下两个函数：
+
+```
+read(file, tmp_buf, len);
+
+write(socket, tmp_buf, len);
+```
+
+
+
+### 2. mmap和sendFile零拷贝
 
 在Java程序中，常用的零拷贝有mmap（内存映射）和sendFile。让我们回到IO底层，在Java中，一次IO操作在操作系统底层都做了哪些工作。