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();    }}