JavaSE系列教程(七十四)
讲解java IO流之管道流。
在UNIX/Linux中有一个很有用的概念——管道（pipe），它具有将一个程序的输出当作另一个程序的输入的能力。管道流的主要作用是可以进行两个线程间的通讯，分为管道输入流（PipeOutputStream和PipedWriter）和管道输出流（PipeInputStream和PipedReader）。
1.如何建立管道
一般我们使用都是先定义一个管道输入流PipedInputStream（或者PipedReader）对象和管道输出流PipedOutputStream（或者PipedWriter）对象，然后将他们关联起来，建立了一条”管道”。
- 使用connect()方法
PipedInputStream pipedInputStream=new PipedInputStream();
PipedOutputStream pipedOutputStream=new PipedOutputStream();
try {
pipedInputStream.connect(pipedOutputStream);
} catch (IOException e) {
e.printStackTrace();
}
- 不使用connect()方法
PipedInputStream pipedInputStream=new PipedInputStream();
PipedOutputStream pipedOutputStream=null;
try {
pipedOutputStream = new PipedOutputStream(pipedInputStream);
} catch (IOException e) {
e.printStackTrace();
}
2.管道流常用方法
++PipeOutputStream和PipedWriter输出方法：++
void write(byte[] b, int off, int len) 将 len 字节从初始偏移量为 off 的指定 byte 数组写入该管道输出流。 void write(char[] b, int off, int len),含义与上类似。
++PipeInputStream和PipedReader输入方法：++
读取文件的方法，将连接的PipeOutputStream对象实例的输入流的数据，通过read方法，把内容读取到数组中。 int read(byte[] b, int off, int len) 将最多 len 个数据字节从此管道输入流读入 byte 数组。 int read(char[] b, int off, int len)，含义与上类似
实例：使用PipedInputStream和PipedOutputStream实现java源文件的复制效果。
class Sender implements Runnable {
private PipedOutputStream out = new PipedOutputStream();
private File srcFile;
public Sender(File srcFile) {
this.srcFile = srcFile;
}
public PipedOutputStream getOutputStream() {
return out;
}
public void run() {
BufferedInputStream bin = null;
try {
bin = new BufferedInputStream(new FileInputStream(this.srcFile));
byte[] buffer = new byte[1024];
int len=-1;
while((len=bin.read(buffer))!=-1){
//System.out.println(s);
out.write(buffer,0,len);
}
} catch (IOException e) {
e.printStackTrace();
}finally {
try{
if(bin!=null){
bin.close();
bin = null;
}
if(out!=null){
out.close();
out=null;
}
}catch(Exception ex){
ex.printStackTrace();
}
}
}
}
class Receiver implements Runnable {
private PipedInputStream in = new PipedInputStream();
private File destFile;
public Receiver(File destFile) {
this.destFile = destFile;
}
public PipedInputStream getInputStream() {
return in;
}
public void run() {
BufferedOutputStream bout = null;
byte[] b = new byte[1024];
try {
bout = new BufferedOutputStream(new FileOutputStream(destFile));
String s = null;
int len = -1;
while((len= in.read(b))!=-1){
bout.write(b,0,len);
}
bout.flush();
} catch (IOException e) {
e.printStackTrace();
}finally{
try{
if(bout!=null){
bout.close();
bout=null;
}
if(in!=null){
in.close();
in = null;
}
}catch(Exception ex){
ex.printStackTrace();
}
}
}
}
public class PipedDemo {
public static void main(String[] args) {
File srcFile = new File("d:" + File.separator + "MyUtils.java");
File destFile = new File("e:" + File.separator + "MyUtils.java");
try {
Sender sender = new Sender(srcFile); // 创建线程对象Sender
Receiver receiver = new Receiver(destFile); // 创建线程对象Receiver
PipedOutputStream out = sender.getOutputStream(); // 写入
PipedInputStream in = receiver.getInputStream(); // 读出
out.connect(in); // 将输出发送到输入
Thread senderThread = new Thread(sender);
Thread receiverThread = new Thread(receiver);
senderThread.start();// 启动线程
receiverThread.start();
} catch (IOException e) {
e.printStackTrace();
}
}
}
因为是读写字符文件，为了提升效率，也可以使用PipedReader和PipedWriter实现java源文件的复制效果。
class Sender implements Runnable {
private PipedWriter out = new PipedWriter();
private File srcFile;
public Sender(File srcFile) {
this.srcFile = srcFile;
}
public PipedWriter getOutputStream() {
return out;
}
public void run() {
BufferedReader bin = null;
char[] b = new char[1024];
try {
bin = new BufferedReader(new FileReader(this.srcFile));
int len=-1;
while((len = bin.read(b))!=-1){
out.write(b,0,len);
}
} catch (IOException e) {
e.printStackTrace();
}finally {
try{
if(bin!=null){
bin.close();
bin = null;
}
if(out!=null){
out.close();
out=null;
}
}catch(Exception ex){
ex.printStackTrace();
}
}
}
}
class Receiver implements Runnable {
private PipedReader in = new PipedReader();
private File destFile;
public Receiver(File destFile) {
this.destFile = destFile;
}
public PipedReader getInputStream() {
return in;
}
public void run() {
BufferedWriter bout = null;
char[] b = new char[1024];
try {
bout = new BufferedWriter(new FileWriter(destFile));
int len = -1;
while((len = in.read(b))!=-1){
bout.write(b,0,len);
}
bout.flush();
} catch (IOException e) {
e.printStackTrace();
}finally{
try{
if(bout!=null){
bout.close();
bout=null;
}
if(in!=null){
in.close();
in = null;
}
}catch(Exception ex){
ex.printStackTrace();
}
}
}
}
public class PipedDemo {
public static void main(String[] args) {
File srcFile = new File("d:" + File.separator + "MyUtils.java");
File destFile = new File("e:" + File.separator + "MyUtils.java");
try {
Sender sender = new Sender(srcFile); // 创建线程对象Sender
Receiver receiver = new Receiver(destFile); // 创建线程对象Receiver
PipedWriter out = sender.getOutputStream(); // 写入
PipedReader in = receiver.getInputStream(); // 读出
out.connect(in); // 将输出发送到输入
Thread senderThread = new Thread(sender);
Thread receiverThread = new Thread(receiver);
senderThread.start();// 启动线程
receiverThread.start();
} catch (IOException e) {
e.printStackTrace();
}
}
}