比如,我需要在a时间执行网络下载,这个时候是需要开启一个线程执行下载,但是在a我又需要用线程执行完,返回的数据,这个时候我们需要主线程的callback方式,用while循环的方式,使得主线程能够等待子线程完成:
eg:
主线程中
public static String getJson(final String jsonUrl) {
ThreadForJson threadForJson =new ThreadForJson();
threadForJson.jsonUrl=jsonUrl;
threadForJson.start();
while(threadForJson.flag==false){
System.out.println("还没准备好"+flag);
}
return threadForJson.result;
}
子线程
package com.baihe.newsconsult.util;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.net.HttpURLConnection;
import java.net.URL;
/**
* Created by
* Project_Name: NewsConsult
* Package_Name: com.baihe.newsconsult.util
* Date: 2019/5/9
* Time: 20:30
*/
public class ThreadForJson extends Thread {
boolean flag=false;
String jsonUrl;
String result;
public ThreadForJson(){
System.out.println("this is ThreadForJson contruct methud!");
}
@Override
public void run() {
System.out.println("this is ThreadForJson RUN");
super.run();
//耗时的网络操作必须要在这种子线程里面去做
URL url = null;
//建立的http链接
HttpURLConnection httpConn = null;
//请求的输入流
BufferedReader in = null;
//输入流的缓冲
StringBuffer sb = new StringBuffer();
try {
url = new URL(jsonUrl);
in = new BufferedReader(new InputStreamReader(url.openStream(), "UTF-8"));
String str = null;
//一行一行进行读入
while ((str = in.readLine()) != null) {
sb.append(str);
}
} catch (Exception ex) {
} finally {
try {
if (in != null) {
in.close(); //关闭流
}
} catch (IOException ex) {
}
}
result = sb.toString();
callback();
}
public void callback()
{
System.out.println("子线程执行结束");
flag=true;
}
}
利用callback方法来人为的让主线程等待;