多线程导入数据

package cn.text;


import java.util.ArrayList;
import java.util.List;
import java.util.concurrent.CountDownLatch;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;


public class Text {



//测试
public static void main(String[] args) {
List<String> list = new ArrayList<String>();
//数据越大线程越多
for (int i = 0; i < 3000000; i++) {
list.add("hello"+i);
}
try {
exec(list);
} catch (InterruptedException e) {
e.printStackTrace();
}
}
public static void exec(List<String> list) throws InterruptedException{
int count = 300;//一个线程处理300条数据
int listSize = list.size();//数据集合大小
int runSize = (listSize/count)+1; //开启的线程数
List<String> newlist = null;//存放每个线程的执行数据
ExecutorService executor = Executors.newFixedThreadPool(runSize);//创建一个线程池，数量和开启线程的数量一样
//创建两个个计数器
CountDownLatch begin = new CountDownLatch(1);
CountDownLatch end = new CountDownLatch(runSize);
//循环创建线程
for (int i = 0; i < runSize ; i++) {
//计算每个线程执行的数据
if((i+1)==runSize){
int startIndex = (i*count);
int endIndex = list.size();
newlist= list.subList(startIndex, endIndex);
}else{
int startIndex = (i*count);
int endIndex = (i+1)*count;
newlist= list.subList(startIndex, endIndex);
}
//线程类
MyThread mythead = new MyThread(newlist,begin,end);
//这里执行线程的方式是调用线程池里的executor.execute(mythead)方法。
executor.execute(mythead);
}

begin.countDown();
end.await();

//执行完关闭线程池
executor.shutdown();
}
//线程类就不另外写了，写在同一个文件里咯，有需要可以分开写
private static class MyThread implements Runnable{
private List<String> list;
private CountDownLatch begin;
private CountDownLatch end;

//创建个构造函数初始化 list,和其他用到的参数
public MyThread(List<String> list,CountDownLatch begin,CountDownLatch end){
this.list = list;
this.begin = begin;
this.end = end;
}

@Override
public void run() {
try {
for (int i = 0; i < list.size(); i++) {
//这里还要说一下，，由于在实质项目中，当处理的数据存在等待超时和出错会使线程一直处于等待状态
//这里只是处理简单的，
System.out.println(list.get(i));
}
//....
//执行完让线程直接进入等待
begin.await();
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}finally{
//这里要主要了，当一个线程执行完 了计数要减一不要这个线程会被一直挂起
//，end.countDown()，这个方法就是直接把计数器减一的
end.countDown();
}
}


}



}