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() {@Overridepublic void run() {try {byte[] bArr = new byte[]{1,2,3};pos.write(bArr);pos.close();} catch (IOException e) {e.printStackTrace();}}});es.execute(new Runnable() {@Overridepublic 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();}
}

转载于:https://www.cnblogs.com/chenpi/p/5367823.html