AsynchronousFileChannel类的使用（二）

- 日理万妓 2021-08-30 23:08 301阅读 0赞

#### 读取数据方式1 ####

`public abstract Future<Integer> read(ByteBuffer dst, long position)`方法的作用是从给定的文件位置开始，从该通道将字节序列读人给定的缓冲区。此方法从给定的文件位置开始，将从该通道的字节序列读取到给定的缓冲区。此方法返回Future对象。如果给定位置大于或等于在尝试读取时文件的大小，则Future 的get()方法将返回读取的字节数或-1。  
此方法的工作方式与`AsynchronousByteChannel.read(ByteBuffer)`方法相同，只是从给定文件位置开始读取字节。如果给定的文件位置大于文件在读取时的大小，则不读取任何字节。参数dst代表要将字节传输到的缓冲区。参数position代表开始的文件位置，必须是非负数。

a.txt文件的内容: 12345。

length=3
    1
    2
    3

#### 读取数据方式2 ####

a.txt文件的内容：12345

public static void main(String[] args) throws Exception{ 
            Path path = Paths.get("a.txt");
            AsynchronousFileChannel channel = AsynchronousFileChannel.open(path, StandardOpenOption.READ);
            ByteBuffer byteBuffer = ByteBuffer.allocate(5);
            channel.read(byteBuffer, 0, "我是附加的参数", new CompletionHandler<Integer, String>() { 
                @Override
                public void completed(Integer result, String attachment) { 
                    System.out.println("public void completed(Integer result, String attachment) result="
                        + result + " attachment=" + attachment);
                }
    
                @Override
                public void failed(Throwable exc, String attachment) { 
                    System.out.println("public void failed(Throwable exc, String attachment) attachment="
                        + attachment);
                    System.out.println("getMessage=" + exc.getMessage());
                }
            });
            Thread.sleep(2000);
            channel.close();
    
            byte[] byteArray = byteBuffer.array();
            for (int i = 0; i < byteArray.length; i++) { 
                System.out.println((char)byteArray[i]);
            }
        }

public void completed(Integer result, String attachment) result=5 attachment=我是附加的参数
    1
    2
    3
    4
    5

#### 写入数据方式1 ####

a.txt文件的内容：12345

public static void main(String[] args) throws Exception{ 
            Path path = Paths.get("a.txt");
            AsynchronousFileChannel channel = AsynchronousFileChannel.open(path, StandardOpenOption.WRITE);
            ByteBuffer byteBuffer = ByteBuffer.wrap("abcde".getBytes());
            Future<Integer> future = channel.write(byteBuffer, channel.size());
            System.out.println("length=" + future.get());
            channel.close();
        }

length=5

a.txt追加写入：  
![在这里插入图片描述][20200611124300407.png]

#### 写入数据方式2 ####

a.txt文件的内容：12345

public static void main(String[] args) throws Exception{ 
            Path path = Paths.get("a.txt");
            AsynchronousFileChannel channel = AsynchronousFileChannel.open(path, StandardOpenOption.WRITE);
            ByteBuffer byteBuffer = ByteBuffer.wrap("abcde".getBytes());
            channel.write(byteBuffer, channel.size(), "我是附加的数据", new CompletionHandler<Integer, String>() { 
                @Override
                public void completed(Integer result, String attachment) { 
                    System.out.println(" public void completed(Integer result, String attachment) result=" +
                            result + " attachment=" + attachment);
                }
    
                @Override
                public void failed(Throwable exc, String attachment) { 
                    System.out.println("public void failed(Throwable exc, String attachment) attachment=" +
                            attachment);
                    System.out.println("getMessage=" + exc.getMessage());
                }
            });
            Thread.sleep(2000);
            channel.close();
        }

public void completed(Integer result, String attachment) result=5 attachment=我是附加的数据

![在这里插入图片描述][20200611124909591.png]

[20200611124300407.png]: /images/20210813/462fe9d7a0494a9bb68c860fef51bd1d.png
[20200611124909591.png]: /images/20210813/44241c8317734801b502e459d28dc714.png