Java多线程处理List数据

Posted 2021-02-12 吃饭了吗饭没了秀

实例1：

解决问题：如何让n个线程顺序遍历含有n个元素的List集合

import java.util.ArrayList;
import java.util.List;
import org.apache.commons.lang3.ArrayUtils;

public class Test_4 {
/**
* 多线程处理list
*
* @param data 数据list
* @param threadNum 线程数
*/
public synchronized void handleList(List<String> data, int threadNum) {
int length = data.size();
int tl = length % threadNum == 0 ? length / threadNum : (length
/ threadNum + 1);

for (int i = 0; i < threadNum; i++) {
int end = (i + 1) * tl;
HandleThread thread = new HandleThread("线程[" + (i + 1) + "] ", data, i * tl, end > length ? length : end);
thread.start();
}
}

class HandleThread extends Thread {
private String threadName;
private List<String> data;
private int start;
private int end;

public HandleThread(String threadName, List<String> data, int start, int end) {
this.threadName = threadName;
this.data = data;
this.start = start;
this.end = end;
}

public void run() {
List<String> subList = data.subList(start, end)/*.add("^&*")*/;
System.out.println(threadName+"处理了"+subList.size()+"条！");
}

}

public static void main(String[] args) {
Test_4 test = new Test_4();
// 准备数据
List<String> data = new ArrayList<String>();
for (int i = 0; i < 6666; i++) {
data.add("item" + i);
}
test.handleList(data, 5);
System.out.println(ArrayUtils.toString(data));
}
}

实例2：

List多线程并发读取读取现有的list对象

//测试读取List的线程类，大概34秒
package com.thread.list;
 
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
 
public class Main {
    
    public static void main(String[] args) {
        
        List<String> list = new ArrayList<String>();
        Map<Long,Integer> map = new HashMap<Long,Integer>();

        for(int i = 0;i<1000;i++){
            list.add(""+i);
        }
        
        int pcount = Runtime.getRuntime().availableProcessors();        
        long start = System.currentTimeMillis();        
        
        for(int i=0;i<pcount;i++){
            
           Thread t = new MyThread1(list,map);
            map.put(t.getId(),Integer.valueOf(i));
            t.start();
            try {
                t.join();
            } catch (InterruptedException e) {              
                e.printStackTrace();
            }            
           // System.out.println(list.get(i));
        }        
        System.out.println("----"+(System.currentTimeMillis() - start));
    }    
}

//线程类
package com.thread.list;
 
import java.util.List;
import java.util.Map;
 
public class MyThread1 extends Thread {
 
    private List<String> list;
    private Map<Long,Integer> map;
    
    public MyThread1(List<String> list,Map<Long,Integer> map){
        this.list = list;
        this.map = map;
    }
    
    @Override
    public void run() {
        
        int pcount = Runtime.getRuntime().availableProcessors();
        int i = map.get(Thread.currentThread().getId());
        
        for(;i<list.size();i+=pcount){
            System.out.println(list.get(i));
        }              
    }    
}

实例3：

多线程分段处理List集合

场景:大数据List集合,需要对List集合中的数据同标准库中数据进行对比,生成新增,更新,取消数据 
解决方案:

1. List集合分段,
2. 动态创建线程池newFixedThreadPool
3. 将对比操作在多线程中实现

   public static void main(String[] args) throws Exception {
   
           // 开始时间
           long start = System.currentTimeMillis();
           List<String> list = new ArrayList<String>();
   
           for (int i = 1; i <= 3000; i++) {
               list.add(i + "");
           }
           // 每500条数据开启一条线程
           int threadSize = 500;
           // 总数据条数
           int dataSize = list.size();
           // 线程数
           int threadNum = dataSize / threadSize + 1;
           // 定义标记,过滤threadNum为整数
           boolean special = dataSize % threadSize == 0;
   
           // 创建一个线程池
           ExecutorService exec = Executors.newFixedThreadPool(threadNum);
           // 定义一个任务集合
           List<Callable<Integer>> tasks = new ArrayList<Callable<Integer>>();
           Callable<Integer> task = null;
           List<String> cutList = null;
   
           // 确定每条线程的数据
           for (int i = 0; i < threadNum; i++) {
               if (i == threadNum - 1) {
                   if (special) {
                       break;
                   }
                   cutList = list.subList(threadSize * i, dataSize);
               } else {
                   cutList = list.subList(threadSize * i, threadSize * (i + 1));
               }
               // System.out.println("第" + (i + 1) + "组：" + cutList.toString());
               final List<String> listStr = cutList;
               task = new Callable<Integer>() {
   
                   @Override
                   public Integer call() throws Exception {
                       System.out.println(Thread.currentThread().getName() + "线程：" + listStr);
                       return 1;
                   }
               };
               // 这里提交的任务容器列表和返回的Future列表存在顺序对应的关系
               tasks.add(task);
           }
   
           List<Future<Integer>> results = exec.invokeAll(tasks);
   
           for (Future<Integer> future : results) {
               System.out.println(future.get());
           }
   
           // 关闭线程池
           exec.shutdown();
           System.out.println("线程任务执行结束");
           System.err.println("执行任务消耗了 ：" + (System.currentTimeMillis() - start) + "毫秒");
       }