详解Java多线程处理List数据

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");
  }

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