使用异步解析 Json url [英] Parsing Json url using async

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本文介绍了使用异步解析 Json url的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！

问题描述

运行此代码时出现异常.我想解析 url，它是一个 json 对象数组:

I get exceptions when running this code. I want to parse the url which is an array of json objects:

package com.example.compsci_734t;

import java.io.BufferedReader;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.net.URL;

import org.apache.http.HttpEntity;
import org.apache.http.HttpResponse;
import org.apache.http.StatusLine;
import org.apache.http.client.HttpClient;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.impl.client.DefaultHttpClient;
import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;

import android.app.Activity;
import android.os.AsyncTask;
import android.os.Bundle;
import android.util.Log;

public class UoaCompsciActivity extends Activity {

    private static String url = " http://redsox.tcs.auckland.ac.nz/734A/CSService.svc/courses";
    //URL requestUrl = new URL(url);
    JSONArray courses = null;
    private static final String TAG_COURSES = "Courses";

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_uoa_compsci);
        new MyTask().execute();
    }


    private class MyTask extends AsyncTask<URL, Void, JSONObject> {

        @Override
        protected JSONObject doInBackground(URL... urls) {
            loadJSON(url);
            return null;
        }

        protected void onPostExecute(JSONObject json) {

            try {
                courses = json.getJSONArray(TAG_COURSES);

                // looping through all courses
                for (int i = 0; i < courses.length(); i++) {
                    JSONObject c = courses.getJSONObject(i);

                    // Storing each json item in variable
                    String course_id = c.getString("courseField:");
                    String course_name = c.getString("titleField:");
                    String course_semester = c.getString("semesterField:");



                    Log.v("--", "Course: 
" + " " + course_id + " " + course_name
                            + " " + course_semester);
                }

        } catch (JSONException e) {
            e.printStackTrace();
        }
    }
    }


    public JSONObject loadJSON(String url) {
        // Creating JSON Parser instance
        JSONParser jParser = new JSONParser();

        // getting JSON string from URL
         JSONObject json = jParser.getJSONFromUrl(url);

        return json;
    }

}

这里还有我的 logcat:

Also here is my logcat: 

05-13 20:29:05.118: I/dalvikvm(770): threadid=3: reacting to signal 3
05-13 20:29:05.128: I/dalvikvm(770): Wrote stack traces to '/data/anr/traces.txt'
05-13 20:29:05.418: D/gralloc_goldfish(770): Emulator without GPU emulation detected.
05-13 20:31:46.128: I/dalvikvm(842): threadid=3: reacting to signal 3
05-13 20:31:46.218: I/dalvikvm(842): Wrote stack traces to '/data/anr/traces.txt'
05-13 20:31:46.408: D/gralloc_goldfish(842): Emulator without GPU emulation detected.
05-13 22:06:17.298: I/dalvikvm(918): threadid=3: reacting to signal 3
05-13 22:06:17.389: I/dalvikvm(918): Wrote stack traces to '/data/anr/traces.txt'
05-13 22:06:17.549: D/gralloc_goldfish(918): Emulator without GPU emulation detected.
05-13 22:06:17.829: W/dalvikvm(918): threadid=11: thread exiting with uncaught exception (group=0x409c01f8)
05-13 22:06:17.839: E/AndroidRuntime(918): FATAL EXCEPTION: AsyncTask #1
05-13 22:06:17.839: E/AndroidRuntime(918): java.lang.RuntimeException: An error occured while executing doInBackground()
05-13 22:06:17.839: E/AndroidRuntime(918):  at android.os.AsyncTask$3.done(AsyncTask.java:278)
05-13 22:06:17.839: E/AndroidRuntime(918):  at java.util.concurrent.FutureTask$Sync.innerSetException(FutureTask.java:273)
05-13 22:06:17.839: E/AndroidRuntime(918):  at java.util.concurrent.FutureTask.setException(FutureTask.java:124)
05-13 22:06:17.839: E/AndroidRuntime(918):  at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:307)
05-13 22:06:17.839: E/AndroidRuntime(918):  at java.util.concurrent.FutureTask.run(FutureTask.java:137)
05-13 22:06:17.839: E/AndroidRuntime(918):  at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:208)
05-13 22:06:17.839: E/AndroidRuntime(918):  at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1076)
05-13 22:06:17.839: E/AndroidRuntime(918):  at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:569)
05-13 22:06:17.839: E/AndroidRuntime(918):  at java.lang.Thread.run(Thread.java:856)
05-13 22:06:17.839: E/AndroidRuntime(918): Caused by: java.lang.IllegalArgumentException: Illegal character in scheme at index 0:  http://redsox.tcs.auckland.ac.nz/734A/CSService.svc/courses
05-13 22:06:17.839: E/AndroidRuntime(918):  at java.net.URI.create(URI.java:727)
05-13 22:06:17.839: E/AndroidRuntime(918):  at org.apache.http.client.methods.HttpPost.<init>(HttpPost.java:79)
05-13 22:06:17.839: E/AndroidRuntime(918):  at com.example.compsci_734t.JSONParser.getJSONFromUrl(JSONParser.java:36)
05-13 22:06:17.839: E/AndroidRuntime(918):  at com.example.compsci_734t.UoaCompsciActivity.loadJSON(UoaCompsciActivity.java:78)
05-13 22:06:17.839: E/AndroidRuntime(918):  at com.example.compsci_734t.UoaCompsciActivity$MyTask.doInBackground(UoaCompsciActivity.java:42)
05-13 22:06:17.839: E/AndroidRuntime(918):  at com.example.compsci_734t.UoaCompsciActivity$MyTask.doInBackground(UoaCompsciActivity.java:1)
05-13 22:06:17.839: E/AndroidRuntime(918):  at android.os.AsyncTask$2.call(AsyncTask.java:264)
05-13 22:06:17.839: E/AndroidRuntime(918):  at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:305)
05-13 22:06:17.839: E/AndroidRuntime(918):  ... 5 more

更新日志:

05-13 22:15:01.438: I/dalvikvm(968): threadid=3: reacting to signal 3
05-13 22:15:01.598: I/dalvikvm(968): Wrote stack traces to '/data/anr/traces.txt'
05-13 22:15:01.718: D/gralloc_goldfish(968): Emulator without GPU emulation detected.
05-13 22:15:02.288: E/JSON Parser(968): Error parsing data org.json.JSONException: Value <?xml of type java.lang.String cannot be converted to JSONObject
05-13 22:15:02.288: D/AndroidRuntime(968): Shutting down VM
05-13 22:15:02.288: W/dalvikvm(968): threadid=1: thread exiting with uncaught exception (group=0x409c01f8)
05-13 22:15:02.298: E/AndroidRuntime(968): FATAL EXCEPTION: main
05-13 22:15:02.298: E/AndroidRuntime(968): java.lang.NullPointerException
05-13 22:15:02.298: E/AndroidRuntime(968):  at com.example.compsci_734t.UoaCompsciActivity$MyTask.onPostExecute(UoaCompsciActivity.java:49)
05-13 22:15:02.298: E/AndroidRuntime(968):  at com.example.compsci_734t.UoaCompsciActivity$MyTask.onPostExecute(UoaCompsciActivity.java:1)
05-13 22:15:02.298: E/AndroidRuntime(968):  at android.os.AsyncTask.finish(AsyncTask.java:602)
05-13 22:15:02.298: E/AndroidRuntime(968):  at android.os.AsyncTask.access$600(AsyncTask.java:156)
05-13 22:15:02.298: E/AndroidRuntime(968):  at android.os.AsyncTask$InternalHandler.handleMessage(AsyncTask.java:615)
05-13 22:15:02.298: E/AndroidRuntime(968):  at android.os.Handler.dispatchMessage(Handler.java:99)
05-13 22:15:02.298: E/AndroidRuntime(968):  at android.os.Looper.loop(Looper.java:137)
05-13 22:15:02.298: E/AndroidRuntime(968):  at android.app.ActivityThread.main(ActivityThread.java:4424)
05-13 22:15:02.298: E/AndroidRuntime(968):  at java.lang.reflect.Method.invokeNative(Native Method)
05-13 22:15:02.298: E/AndroidRuntime(968):  at java.lang.reflect.Method.invoke(Method.java:511)
05-13 22:15:02.298: E/AndroidRuntime(968):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:784)
05-13 22:15:02.298: E/AndroidRuntime(968):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:551)
05-13 22:15:02.298: E/AndroidRuntime(968):  at dalvik.system.NativeStart.main(Native Method)
05-13 22:15:02.889: I/dalvikvm(968): threadid=3: reacting to signal 3
05-13 22:15:02.919: I/dalvikvm(968): Wrote stack traces to '/data/anr/traces.txt'

完整日志:05-13 22:15:01.438: I/dalvikvm(968): threadid=3: 对信号 3 做出反应05-13 22:15:01.598:I/dalvikvm(968):将堆栈跟踪写入/data/anr/traces.txt"05-13 22:15:01.718: D/gralloc_goldfish(968): 没有检测到 GPU 仿真的模拟器.05-13 22:15:02.288: E/JSON Parser(968): 解析数据时出错 org.json.JSONException: Value 

full logcat: 05-13 22:15:01.438: I/dalvikvm(968): threadid=3: reacting to signal 3 05-13 22:15:01.598: I/dalvikvm(968): Wrote stack traces to '/data/anr/traces.txt' 05-13 22:15:01.718: D/gralloc_goldfish(968): Emulator without GPU emulation detected. 05-13 22:15:02.288: E/JSON Parser(968): Error parsing data org.json.JSONException: Value 

推荐答案

错误本身就是说明性的:

The error is explanatory itself:

java.lang.IllegalArgumentException: 方案中的非法字符在索引 0

java.lang.IllegalArgumentException: Illegal character in scheme at index 0

您需要删除 URL 中的开头空格字符:

You need to remove the beginning space character in your URL:

private static String url = "http://redsox.tcs.auckland.ac.nz/734A/CSService.svc/courses";

<小时>

更新:

更新问题后，现在问题出现在这一行:

After you've updated your question, now the problem seems in this line:

courses = json.getJSONArray(TAG_COURSES);

因为您还没有初始化或设置 courses 的值，这就是它给出 NullPointerException 错误的原因.

because you haven't initialized or set the value of courses that's why its giving NullPointerException error.

这篇关于使用异步解析 Json url的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！

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