字节流InputStream/OutputStream

本篇将对JAVA I/O流中的字节流InputStream/OutputStream做个简单的概括:

总得来说，每个字节流类都有一个对应的用途，如下：

ByteArrayInputStream/ByteArrayOutputStream //字节数组相关
FileInputStream/FileOutputStream //文件操作相关
PipedOutputStream/PipedInputStream //线程间通信（管道）
BufferedInputStream/BufferedOutputStream //装饰其它字节流，增加缓冲功能
FilterInputStream/FilterOutputStream //装饰其它字节流，增加一些过滤处理
PushbackInputStream //装饰其它字节流，增加回退读取功能
DataOutputStream/DataInputStream //装饰其它字节流，增加对JAVA基本数据类型的读取/写入功能
PrintStream //装饰其它字节流，增加格式化数据写入功能
ObjectInputStream/ObjectOutputStream //装饰其它字节流，增加对象的序列化，以字节形式读取/写入到本地文件
SequenceInputStream //以串行形式连接若干字节输入流

再看下字节流InputStream/OutputStream的组成结构,如下图；

接下来逐个介绍；

ByteArrayInputStream/ByteArrayOutputStream

简单地说，就是字节数组与字节输入输出流之间的各种转换，举个例子如下：

package io;

import java.io.ByteArrayInputStream;

import java.io.ByteArrayOutputStream;

import java.io.IOException;

import java.io.InputStream;

public class IOTest {

    public static void main(String[] args) throws IOException {

        //内存中的字节数组

        byte[] bArr = new byte[]{1,2,3};

        //字节输入流

        InputStream is = new ByteArrayInputStream(bArr);

        //字节输出流

        ByteArrayOutputStream bos = new ByteArrayOutputStream();

        byte[] bff = new byte[3];

        //从输入流中读取字节

        is.read(bff,0,3);

        System.out.println(bff[0] + "," + bff[1] + "," + bff[2]);

        //往字节输出流中写入字节数组

        bos.write(bff);

        //从输出流中获取字节数组

        byte[] bArryFromOs = bos.toByteArray();

        System.out.println(bArryFromOs[0] + "," + bArryFromOs[1] + "," + bArryFromOs[2]);

        is.close();
        bos.close();

    }

}

FileInputStream/FileOutputStream

可以用FileInputStream/FileOutputStream对文件进行写入及读取，如下代码，可以实现文件的复制：

package io;

import java.io.FileInputStream;

import java.io.FileOutputStream;

import java.io.IOException;

import java.io.InputStream;

import java.io.OutputStream;

public class IOTest {

    public static void main(String[] args) throws IOException {

        // 字节输入流

        InputStream is = new FileInputStream("C:\\test.jpg");

        // 字节输出流

        OutputStream os = new FileOutputStream("C:\\copy_test.jpg", false);

        int bTmp = -1;

        while ((bTmp = is.read()) != -1) {

            os.write(bTmp);

        }

        is.close();

        os.close();

    }

}

PipedOutputStream/PipedInputStream

可用于同一个JVM中的两个线程间通信，字节流传输，举个例子：

package io;

import java.io.IOException;

import java.io.PipedInputStream;

import java.io.PipedOutputStream;

import java.util.concurrent.ExecutorService;

import java.util.concurrent.Executors;

public class IOTest {

    public static void main(String[] args) throws IOException {

        final PipedOutputStream pos = new PipedOutputStream();

        final PipedInputStream pis = new PipedInputStream(pos);

        ExecutorService es = Executors.newFixedThreadPool(2);

        es.execute(new Runnable() {

            @Override

            public void run() {

                try {

                    byte[] bArr = new byte[]{1,2,3};

                    pos.write(bArr);

                    pos.close();

                } catch (IOException e) {

                    e.printStackTrace();

                }

            }

        });

        es.execute(new Runnable() {

            @Override

            public void run() {

                byte[] bArr = new byte[3];

                try {

                    // 会导致线程阻塞

                    pis.read(bArr, 0, 3);

                    pis.close();

                } catch (IOException e) {

                    e.printStackTrace();

                }

                System.out.println(bArr[0] + "," + bArr[1] + "," + bArr[2]);

            }

        });

    }

}

BufferedInputStream/BufferedOutputStream

带缓冲区的字节流，装饰器模式在jdk中的一个应用，可用于装饰其它字节流；

一次读取/写入一大块字节到缓冲区，避免每次频繁访问外部媒介，提高性能；

下面是一个例子：

package io;

import java.io.BufferedInputStream;

import java.io.BufferedOutputStream;

import java.io.FileInputStream;

import java.io.FileOutputStream;

import java.io.IOException;

public class IOTest {

    public static void main(String[] args) throws IOException {

        // 字节输入流

        BufferedInputStream is = new BufferedInputStream(new FileInputStream("C:\\test.jpg"), 10 * 1024);

        // 字节输出流

        BufferedOutputStream os = new BufferedOutputStream(new FileOutputStream("C:\\copy_test.jpg", false));

        int bTmp = -1;

        while ((bTmp = is.read()) != -1) {

            os.write(bTmp);

        }

        is.close();

        os.close();

    }

}

FilterInputStream/FilterOutputStream

可装饰其它字节流，实现自定义过滤字节流的基类，基本上是简单的覆盖了InputStream/OutputStream中的方法，意义不是很大；

PushbackInputStream

可装饰其它字节输入流，增加的功能是是回退读取，如下例子：

package io;

import java.io.ByteArrayInputStream;

import java.io.IOException;

import java.io.PushbackInputStream;

public class IOTest {

    public static void main(String[] args) throws IOException {

        byte[] bArr = new byte[] { 1, 2, 3 };

        // 字节输入流

        PushbackInputStream pis = new PushbackInputStream(new ByteArrayInputStream(bArr));

        System.out.println(pis.read());

        System.out.println(pis.read());

        // 回退

        pis.unread(1);

        System.out.println(pis.read());

        pis.close();

    }

}

DataOutputStream/DataInputStream

可装饰其它字节输入流，增加从输入流中读取Java基本类型数据的功能；

举个例子：

package io;

import java.io.DataInputStream;

import java.io.DataOutputStream;

import java.io.FileInputStream;

import java.io.FileOutputStream;

import java.io.IOException;

public class IOTest {

    public static void main(String[] args) throws IOException {

        // 字节输入流

        DataOutputStream dos = new DataOutputStream(new FileOutputStream("C:\\data.data"));

        DataInputStream dis = new DataInputStream(new FileInputStream("C:\\data.data"));

        dos.writeDouble(2.0235);

        dos.writeInt(520);

        dos.flush();

        System.out.println(dis.readDouble());

        System.out.println(dis.readInt());

        dos.close();

        dis.close();

    }

}

PrintStream

PrintStream可以装饰其它字节输出流，允许将格式化数据写入到字节输出流中，如下示例，将格式化数据写到控制台上；

package io;

import java.io.IOException;

import java.io.PrintStream;

public class IOTest {

    public static void main(String[] args) throws IOException {

        // 字节输出流

        PrintStream ps = System.out;

        //输出格式化数据

        ps.println("hello");

        ps.printf("%5d\n", 101);

        ps.write('2');

        ps.close();

    }

}

ObjectInputStream/ObjectOutputStream

可以装饰其它字节输出流，主要用于对象序列化，可以将一个对象以字节流的形式写入/读取到本地文件中，如下例子：

package io;

import java.io.FileInputStream;

import java.io.FileOutputStream;

import java.io.IOException;

import java.io.ObjectInputStream;

import java.io.ObjectOutputStream;

import java.io.Serializable;

class Dog implements Serializable {

    /**

     *

     */

    private static final long serialVersionUID = -3581113588185842098L;

    private int age;

    public Dog(int age) {

        this.age = age;

    }

    public int getAge() {

        return this.age;

    }

}

public class IOTest {

    public static void main(String[] args) throws IOException, ClassNotFoundException {

        ObjectOutputStream output = new ObjectOutputStream(new FileOutputStream("C:\\object.data"));

        ObjectInputStream input = new ObjectInputStream(new FileInputStream("C:\\object.data"));

        Dog dog = new Dog(2);

        output.writeObject(dog);

        output.flush();

        Dog obj = (Dog) input.readObject();

        System.out.println(obj.getAge());

        output.close();

        input.close();

    }

}

SequenceInputStream

把一个或者多个InputStream串行连接起来，第一个流读完，继续读取第二个流，如下例子

package io;

import java.io.ByteArrayInputStream;

import java.io.IOException;

import java.io.InputStream;

import java.io.SequenceInputStream;

public class IOTest {

    public static void main(String[] args) throws IOException {

        // 内存中的字节数组

        byte[] bArr = new byte[] { 1, 2, 3 };

        byte[] bArr2 = new byte[] { 4, 5, 6 };

        // 字节输入流

        InputStream is = new ByteArrayInputStream(bArr);

        // 字节输入流

        InputStream is2 = new ByteArrayInputStream(bArr2);

        // 字节输入流，连接以上两个流

        SequenceInputStream sis = new SequenceInputStream(is, is2);

        byte[] bff = new byte[3];

        // 从输入流中读取字节

        sis.read(bff, 0, 3);

        System.out.println(bff[0] + "," + bff[1] + "," + bff[2]);

        // 会从第二个字节流读取数据

        sis.read(bff, 0, 3);

        System.out.println(bff[0] + "," + bff[1] + "," + bff[2]);

        is.close();

        is2.close();

        sis.close();

    }

}