字节流InputStream/OutputStream

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();
    }
}