求解为什么Log.d("xyz", jsonString)的jsonString值显示为null

Question

package com.example.news;import java.io.BufferedReader;import java.net.URL;import java.io.IOException;import java.io.InputStream;import java.io.InputStreamReader;import java.io.UnsupportedEncodingException;import java.net.MalformedURLException;import java.util.ArrayList;import java.util.List;import android.app.Activity;import android.os.AsyncTask;import android.os.Bundle;import android.util.Log;import android.widget.ListView;public class MainActivity extends Activity { private static String URL = "http://www.imooc.com/api/teacher?type=4&num=30"; private ListView listView;     @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_main);        listView = (ListView) findViewById(R.id.mainListView);                new NewAsyncTask().execute(URL);            }        private List<NewsBean> getJsonDate(String url)    {    List<NewsBean> newBeanList = new ArrayList<NewsBean>();    try { String jsonString = readStream(new URL(url).openStream()); Log.d("xyz", jsonString); } catch (MalformedURLException e) { // TODO Auto-generated catch block e.printStackTrace(); } catch (IOException e) { // TODO Auto-generated catch block e.printStackTrace(); }    return newBeanList;        }        private String readStream(InputStream is){        InputStreamReader isr;    String result = "";    try {    String line = ""; isr = new InputStreamReader(is,"utf-8"); BufferedReader br = new BufferedReader(isr); while ((line = br.readLine())!=null); { result += line; } } catch (UnsupportedEncodingException e) { // TODO Auto-generated catch block e.printStackTrace(); } catch (IOException e) { // TODO Auto-generated catch block e.printStackTrace(); }    return result;        }    class NewAsyncTask extends AsyncTask<String, Void, List<NewsBean>>{ @Override protected List<NewsBean> doInBackground(String... arg0) { // TODO Auto-generated method stub return getJsonDate(arg0[0]); }        }}

Answer 1

我知道问题出在那里了，是网址错。

Answer 2

Log.d("xyz", jsonString);在执行完String jsonString = readStream(new URL(url).openStream());这句后就马上执行了，还没有从url拿到结果呢。