最近專案中需要從網站上抓取大量的資料，採用了多執行緒技術，每個執行緒抓取的資料都需要儲存到一個檔案中，避免消耗大量的記憶體。

思路：多個訪問執行緒將需要寫入到檔案中的資料先儲存到一個佇列裡面，然後由專門的 寫出執行緒負責從佇列中取出資料並寫入到檔案中。

WriterQueue.java 存放要輸出的資料佇列

package com.yulore.write;

import java.util.LinkedList;
import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;

public class WriterQueue {

	private static final int MAX_QUEUE_SIZE = 5000;
	private LinkedList<String> queue = new LinkedList<String>();
	private Lock lock = new ReentrantLock();
	private Condition notFull = lock.newCondition();
	private Condition notEmpty = lock.newCondition();
	
	private static WriterQueue manager = new WriterQueue();
	
	private WriterQueue(){
		
	}
	
	public static WriterQueue getQueue(){
		
		return manager;
	}
	
	public void put(String phone){
		
		lock.lock();
		
		try {
			while (queue.size() == MAX_QUEUE_SIZE) {
				System.out.println("warning: data queue is full!");
				notFull.await();
			}

			queue.addFirst(phone);
			
			notEmpty.signal();
		} catch (InterruptedException e) {
			e.printStackTrace();
		} finally{
			lock.unlock();
		}
	}
	
	public LinkedList<String> takeAll(){
		
		LinkedList<String> retVal = new LinkedList<String>();
		
		lock.lock();
		
		try {
			while (queue.size() == 0) {
				System.out.println("warning: data queue is empty!");
				notEmpty.await();
			}
			
			retVal.addAll(queue);
//			for(String str : queue){
//				retVal.add(str);
//			}
			//清空佇列
			queue.clear();
			
			notFull.signal();
		} catch (InterruptedException e) {
			e.printStackTrace();
		} finally{
			lock.unlock();
		}
		return retVal;
	}
}
 

package com.yulore.write;

public class WriteTask_New implements Runnable {
	

	@Override
	public void run() {
		for(int i=0;i<20;i++){
//			try {
//				sleep(100);
//			} catch (InterruptedException e) {
//				e.printStackTrace();
//			}
			WriterQueue.getQueue().put("for:"+i+" thread:"+Thread.currentThread().getName());
		}
	}

	private void sleep(int millis) throws InterruptedException {
		Thread.sleep(millis);
	}
	
}
 

package com.yulore.write;

import java.io.BufferedWriter;
import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.OutputStreamWriter;
import java.util.LinkedList;

public class OutputTask implements Runnable {
	private String fileName;
	
	public OutputTask(String fileName) {
		this.fileName = fileName;
	}
	@Override
	public void run() {
		
		while(true){
			try {
				sleep(5000);
			} catch (InterruptedException e) {
				e.printStackTrace();
			}
			LinkedList<String> list = WriterQueue.getQueue().takeAll();
			write2Disk(list);
			list = null;
		}
	}

	private void write2Disk(LinkedList<String> list) {
		
		if(list==null ||list.size()==0){
			System.out.println("no data...");
			return;
		}
		
		System.out.println("開始序列化資料 "+fileName);
		
		String path = "D:/fbb/myWorkSpace_DW07/";
		File outputFile = new File(path+fileName);
		
		if(outputFile==null ||!outputFile.exists()){
			try {
				outputFile.createNewFile();
			} catch (IOException e) {
				e.printStackTrace();
			}
		}
		
		FileOutputStream out = null;
		OutputStreamWriter writer = null;
		BufferedWriter bw = null;
		
		try {
			out = new FileOutputStream(outputFile, true);
			writer = new OutputStreamWriter(out);
			bw = new BufferedWriter(writer);
			
			for(String content : list){
				bw.write(content);
				bw.newLine();
				bw.flush();
			}
			
		} catch (IOException e) {
			e.printStackTrace();
		}finally{
			try {
				if(bw!=null)
					bw.close();
			} catch (IOException e) {
				e.printStackTrace();
			}
		}
	}
	
	private void sleep(int millis) throws InterruptedException {
		Thread.sleep(millis);
	}

}
 

package com.yulore.write;

public class TestWrite {

	/**
	 * @param args
	 */
	public static void main(String[] args) {
		
//		test();
		test02();
	}

	private static void test02() {
		WriteTask_New write = new WriteTask_New();
		for(int i=0;i<4;i++){
			new Thread(write).start();
		}
		
		OutputTask output = new OutputTask("abc.txt");
		new Thread(output).start();
	}

	private static void test() {
		WriteTask write = new WriteTask("abc.txt");
		for(int i=0;i<5;i++){
			new Thread(write).start();
		}
	}
}