多线程写文件问题解答

问题 ：

4个线程 线程1 打印A 线程2打印B 线程3打印C 线程4打印D        向文件1中写入ABCDABCDABCD...     向文件2写入BCDABCDA......  向文件3写入CDABCDAB......  向文件4写入DABCDABC......

 

解答源码：

 

package com.test.play;import java.io.BufferedWriter;import java.io.File;import java.io.FileOutputStream;import java.io.OutputStreamWriter;import java.util.concurrent.locks.Condition;import java.util.concurrent.locks.Lock;import java.util.concurrent.locks.ReentrantLock;public class Test {public static void main(String[] args) {final Task task = new Task();/** * 线程1，输出A */new Thread(new Runnable() {@Overridepublic void run() {for (int i = 0; i < 10; i++) {task.outputA();}}}, "线程1，输出A").start();/** * 线程2，输出B */new Thread(new Runnable() {@Overridepublic void run() {for (int i = 0; i < 10; i++) {task.outputB();}}}, "线程2，输出B").start();/** * 线程3，输出C */new Thread(new Runnable() {@Overridepublic void run() {for (int i = 0; i < 10; i++) {task.outputC();}}}, "线程3，输出C").start();/** * 线程4，输出D */new Thread(new Runnable() {@Overridepublic void run() {for (int i = 0; i < 10; i++) {task.outputD();}}}, "线程4，输出D").start();}public static class Task {private Lock lock = new ReentrantLock();private BufferedWriter bw1 = null;private BufferedWriter bw2 = null;private BufferedWriter bw3 = null;private BufferedWriter bw4 = null;// 用于控制每一轮输出，对于每一轮，每个线程都要分别向不同的文件中输入相应的内容private int ctl = 0;/** * 以下四个condition，用于控制四个线程的同步！ */private Condition cond1 = lock.newCondition();private Condition cond2 = lock.newCondition();private Condition cond3 = lock.newCondition();private Condition cond4 = lock.newCondition();/** * 用于控制，每一轮必须所有的线程工作完毕后，才开始下一轮 */private boolean[] outputThisRound = { false, true, true, true };public Task() {try {// 可以将内容输出的bin目录中/*URL fileFolderPath = Test.class.getClassLoader().getResource("com/test/play");bw1 = new BufferedWriter(new OutputStreamWriter(new FileOutputStream(fileFolderPath.getFile() + "file1.txt")));bw2 = new BufferedWriter(new OutputStreamWriter(new FileOutputStream(fileFolderPath.getFile() + "file2.txt")));bw3 = new BufferedWriter(new OutputStreamWriter(new FileOutputStream(fileFolderPath.getFile() + "file3.txt")));bw4 = new BufferedWriter(new OutputStreamWriter(new FileOutputStream(fileFolderPath.getFile() + "file4.txt")));*/// 将内容输出到 D 盘  A B C D 四个文件中bw1 = new BufferedWriter(new OutputStreamWriter(new FileOutputStream(new File("D:/A.txt"))));bw2 = new BufferedWriter(new OutputStreamWriter(new FileOutputStream(new File("D:/B.txt"))));bw3 = new BufferedWriter(new OutputStreamWriter(new FileOutputStream(new File("D:/C.txt"))));bw4 = new BufferedWriter(new OutputStreamWriter(new FileOutputStream(new File("D:/D.txt"))));} catch (Exception e) {e.printStackTrace();}}public void outputA() {lock.lock();try {while(outputThisRound[0]) {System.out.println("outputA begin to await!");cond1.await();}if (ctl % 4 == 0) {bw1.write("A");bw1.flush();} else if (ctl % 4 == 1) {bw4.write("A");bw4.flush();} else if (ctl % 4 == 2) {bw3.write("A");bw3.flush();} else if (ctl % 4 == 3) {bw2.write("A");bw2.flush();}outputThisRound[0] = true;outputThisRound[1] = false;System.out.println("outputA signal outputB!");cond2.signal();} catch (Exception e) {e.printStackTrace();} finally {lock.unlock();}}public void outputB() {lock.lock();try {while(outputThisRound[1]) {System.out.println("outputB begin to await!");cond2.await();}if (ctl % 4 == 0) {bw2.write("B");bw2.flush();} else if (ctl % 4 == 1) {bw1.write("B");bw1.flush();} else if (ctl % 4 == 2) {bw4.write("B");bw4.flush();} else if (ctl % 4 == 3) {bw3.write("B");bw3.flush();}outputThisRound[1] = true;outputThisRound[2] = false;System.out.println("outputB signal outputC!");cond3.signal();} catch (Exception e) {e.printStackTrace();} finally {lock.unlock();}}public void outputC() {lock.lock();try {while(outputThisRound[2]) {System.out.println("outputC begin to await!");cond3.await();}if (ctl % 4 == 0) {bw3.write("C");bw3.flush();} else if (ctl % 4 == 1) {bw2.write("C");bw2.flush();} else if (ctl % 4 == 2) {bw1.write("C");bw1.flush();} else if (ctl % 4 == 3) {bw4.write("C");bw4.flush();}outputThisRound[2] = true;outputThisRound[3] = false;System.out.println("outputC signal outputD!");cond4.signal();} catch (Exception e) {e.printStackTrace();} finally {lock.unlock();}}public void outputD() {lock.lock();try {while(outputThisRound[3]) {System.out.println("outputD begin to await!");cond4.await();}if (ctl % 4 == 0) {bw4.write("D");bw4.flush();} else if (ctl % 4 == 1) {bw3.write("D");bw3.flush();} else if (ctl % 4 == 2) {bw2.write("D");bw2.flush();} else if (ctl % 4 == 3) {bw1.write("D");bw1.flush();}outputThisRound[3] = true;outputThisRound[0] = false;ctl++;System.out.println("outputD signal outputA!");cond1.signal();} catch (Exception e) {e.printStackTrace();} finally {lock.unlock();}}}}