新增:映射文件的使用

Author: JeffLi1993

src/org/javacore/nio/LockingMappedFiles.java

@@ -0,0 +1,75 @@
+package org.javacore.nio;
+
+import java.io.FileNotFoundException;
+import java.io.IOException;
+import java.io.RandomAccessFile;
+import java.nio.ByteBuffer;
+import java.nio.MappedByteBuffer;
+import java.nio.channels.FileChannel;
+import java.nio.channels.FileLock;
+
+/*
+ * Copyright [2015] [Jeff Lee]
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+/**
+ * @author Jeff Lee
+ * @since 2015-10-17 15:17:04
+ * 映射文件的使用
+ */
+public class LockingMappedFiles {
+    static final int LENGTH = 0x8FFFFFF; // 128 MB
+    static FileChannel fc;
+
+    public static void main(String[] args) throws IOException {
+        fc = new RandomAccessFile("data.txt" , "rw").getChannel();
+        MappedByteBuffer out = fc.map(FileChannel.MapMode.READ_WRITE,
+                0 , LENGTH);
+        for (int i = 0;i < LENGTH; i++)
+            out.put((byte)'x');
+        new LockAndModify(out,0,0 + LENGTH/3);
+        new LockAndModify(out,LENGTH/2,LENGTH/2 + LENGTH/4);
+    }
+
+    // 线程
+    private static class LockAndModify extends Thread {
+        private ByteBuffer buffer;
+        private int start,end;
+
+        LockAndModify(ByteBuffer mbb, int start, int end) {
+            this.start = start;
+            this.end = end;
+            mbb.limit(end);
+            mbb.position(start);
+            buffer = mbb.slice();
+            start();
+        }
+
+        public void run() {
+            try {
+                // 从FileChannel获取文件加锁对象，并加锁
+                FileLock fl = fc.lock(start,end,false);
+                System.out.println("Locked: " + start + " to " + end);
+                // 写入数据
+                while (buffer.position() < buffer.limit() - 1)
+                    buffer.put((byte)(buffer.get() + 1));
+                fl.release();
+                System.out.println("Released: " + start + " to " + end);
+            } catch (IOException e) {
+                throw  new RuntimeException(e);
+            }
+        }
+    }
+}