Question

我是android新手我使用以下代码来解析数据并与数据库连接，从而获得服务器中存在的数据库中的值。

我使用的代码是： -

package com.example.library;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.UnsupportedEncodingException;

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

import android.util.Log;

public class JSONParser {

    static InputStream is = null;
    static JSONObject jObj = null;
    static String json = "";

    // constructor
    public JSONParser() {

    }

    public JSONObject getJSONFromUrl(String url) {

        // Making HTTP request
        try {
            // defaultHttpClient
            DefaultHttpClient httpClient = new DefaultHttpClient();
            HttpGet httpGet = new HttpGet(url);

            HttpResponse httpResponse = httpClient.execute(httpGet);
            HttpEntity httpEntity = httpResponse.getEntity();
            is = httpEntity.getContent();          

        } catch (UnsupportedEncodingException e) {
            e.printStackTrace();
        } catch (ClientProtocolException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }

        try {
            BufferedReader reader = new BufferedReader(new InputStreamReader(
                    is, "iso-8859-1"), 8);
            StringBuilder sb = new StringBuilder();
            String line = null;
            while ((line = reader.readLine()) != null) {
                sb.append(line + "\n");
            }
            is.close();
            json = sb.toString();         <------Here
        } catch (Exception e) {
            Log.e("Buffer Error", "Error converting result " + e.toString());
        }

        // try parse the string to a JSON object
        try {
            jObj = new JSONObject(json);
        } catch (JSONException e) {
            Log.e("JSON Parser", "Error parsing data " + e.toString());
        }

        // return JSON String
        return jObj;

    }
   /* public void writeJSON() {
          JSONObject object = new JSONObject();
          try {
            object.put("name", "Prathamesh");
            object.put("score", new Integer(200));
            object.put("current", new Double(152.32));
            object.put("nickname", "Programmer");
          } catch (JSONException e) {
            e.printStackTrace();
          }
          System.out.println(object);
        } 
*/
}

我正在使用另一个代码来使用json的值并显示它。它如下： -

package com.example.library;

import java.util.ArrayList;
import java.util.HashMap;

import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;

import android.app.Activity;
import android.os.Bundle;


public class SecondActivity extends Activity 
{

//url to make request
private static String url = "http://192.168.0.100:3000/users.json";

// JSON Node names
private static final String TAG_ID = "id";
private static final String TAG_FIRST = "first_name";
private static final String TAG_MIDDLE = "middle_name";
private static final String TAG_LAST = "last_name";
private static final String TAG_EMAIL = "email";
private static final String TAG_ADDRESS = "address";
private static final String TAG_MOBILE = "mobile";

private static final String TAG_USERS = "user";

// users JSONArray
JSONArray users = null;



        @Override

    protected void onCreate(Bundle savedInstanceState) {
        // TODO Auto-generated method stub
        super.onCreate(savedInstanceState);
        setContentView(R.layout.tab_test1);


        // Hashmap for ListView
          ArrayList<HashMap<String, String>> userList = new ArrayList<HashMap<String, String>>();

            // Creating JSON Parser instance
            JSONParser jParser = new JSONParser();

            // getting JSON string from URL
            JSONObject json = jParser.getJSONFromUrl(url); <---url I am using is http://192.168.0.100:3000/users.json

            try {
                // Getting Array of Contacts
            users = json.getJSONArray(TAG_USERS);

                // looping through All Contacts
                for(int i = 0; i < users.length(); i++){
                    JSONObject c = users.optJSONObject(i);

                    // Storing each json item in variable
                    String id = c.getString(TAG_ID);
                    String first = c.getString(TAG_FIRST);
                    String middle = c.getString(TAG_MIDDLE);
                    String last = c.getString(TAG_LAST);
                    String email = c.getString(TAG_EMAIL);
                    String address = c.getString(TAG_ADDRESS);
                    String mobile = c.getString(TAG_MOBILE);




                    // creating new HashMap

                    HashMap<String, String> map = new HashMap<String, String>();

                    // adding each child node to HashMap key => value
                    map.put(TAG_ID, id);
                    map.put(TAG_FIRST, first);
                    map.put(TAG_MIDDLE,middle);
                    map.put(TAG_LAST, last);
                    map.put(TAG_ADDRESS, address);
                    map.put(TAG_MOBILE, mobile);
                    map.put(TAG_EMAIL, email);

                    // adding HashList to ArrayList
                    userList.add(map);
                }
            } catch (JSONException e) {
                e.printStackTrace();
            }

        }

    }

我的错误日志文件是： -

04-30 16:24:05.697: E/AndroidRuntime(687): FATAL EXCEPTION: main
04-30 16:24:05.697: E/AndroidRuntime(687): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.library/com.example.library.SecondActivity}: java.lang.IllegalArgumentException: HTTP entity may not be null
04-30 16:24:05.697: E/AndroidRuntime(687):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1647)
04-30 16:24:05.697: E/AndroidRuntime(687):  at android.app.ActivityThread.startActivityNow(ActivityThread.java:1487)
04-30 16:24:05.697: E/AndroidRuntime(687):  at android.app.LocalActivityManager.moveToState(LocalActivityManager.java:127)
04-30 16:24:05.697: E/AndroidRuntime(687):  at android.app.LocalActivityManager.startActivity(LocalActivityManager.java:339)
04-30 16:24:05.697: E/AndroidRuntime(687):  at android.widget.TabHost$IntentContentStrategy.getContentView(TabHost.java:654)
04-30 16:24:05.697: E/AndroidRuntime(687):  at android.widget.TabHost.setCurrentTab(TabHost.java:326)
04-30 16:24:05.697: E/AndroidRuntime(687):  at android.widget.TabHost$2.onTabSelectionChanged(TabHost.java:132)
04-30 16:24:05.697: E/AndroidRuntime(687):  at android.widget.TabWidget$TabClickListener.onClick(TabWidget.java:456)
04-30 16:24:05.697: E/AndroidRuntime(687):  at android.view.View.performClick(View.java:2485)
04-30 16:24:05.697: E/AndroidRuntime(687):  at android.view.View$PerformClick.run(View.java:9080)
04-30 16:24:05.697: E/AndroidRuntime(687):  at android.os.Handler.handleCallback(Handler.java:587)
04-30 16:24:05.697: E/AndroidRuntime(687):  at android.os.Handler.dispatchMessage(Handler.java:92)
04-30 16:24:05.697: E/AndroidRuntime(687):  at android.os.Looper.loop(Looper.java:123)
04-30 16:24:05.697: E/AndroidRuntime(687):  at android.app.ActivityThread.main(ActivityThread.java:3683)
04-30 16:24:05.697: E/AndroidRuntime(687):  at java.lang.reflect.Method.invokeNative(Native Method)
04-30 16:24:05.697: E/AndroidRuntime(687):  at java.lang.reflect.Method.invoke(Method.java:507)
04-30 16:24:05.697: E/AndroidRuntime(687):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:839)
04-30 16:24:05.697: E/AndroidRuntime(687):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:597)
04-30 16:24:05.697: E/AndroidRuntime(687):  at dalvik.system.NativeStart.main(Native Method)
04-30 16:24:05.697: E/AndroidRuntime(687): Caused by: java.lang.IllegalArgumentException: HTTP entity may not be null
04-30 16:24:05.697: E/AndroidRuntime(687):  at org.apache.http.util.EntityUtils.toString(EntityUtils.java:110)
04-30 16:24:05.697: E/AndroidRuntime(687):  at org.apache.http.util.EntityUtils.toString(EntityUtils.java:146)
04-30 16:24:05.697: E/AndroidRuntime(687):  at com.example.library.JSONParser.getJSONFromUrl(JSONParser.java:55)
04-30 16:24:05.697: E/AndroidRuntime(687):  at com.example.library.SecondActivity.onCreate(SecondActivity.java:51)
04-30 16:24:05.697: E/AndroidRuntime(687):  at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047)
04-30 16:24:05.697: E/AndroidRuntime(687):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1611)

使用代码json = sb.toString();时，我得到了value.where，json从第二个代码中调用数据库中的一些值。

如果代码有任何问题，请帮助我并告诉我

Answer 1

String retSrc = EntityUtils.toString(httpEntity); 
           // parsing JSON
JSONObject json = new JSONObject(retSrc); //Convert String to JSON Object

而不是

  try {
            BufferedReader reader = new BufferedReader(new InputStreamReader(
                    is, "iso-8859-1"), 8);
            StringBuilder sb = new StringBuilder();
            String line = null;
            while ((line = reader.readLine()) != null) {
                sb.append(line + "\n");
            }
            is.close();
            json = sb.toString();         <------Here
   } catch (Exception e) {
            Log.e("Buffer Error", "Error converting result " + e.toString());
   }

编辑：我对方法的看法如下：

public JSONArray getJSONFromUrl(String url) {
     JSONArray json = null;
    // Making HTTP request
    try {
        // defaultHttpClient
        DefaultHttpClient httpClient = new DefaultHttpClient();
        HttpGet httpGet = new HttpGet(url);

        HttpResponse httpResponse = httpClient.execute(httpGet);
        if (httpResponse != null && httpResponse.getStatusLine().getStatusCode() == 200) {
            HttpEntity httpEntity = httpResponse.getEntity();
            String retSrc = EntityUtils.toString(httpEntity); 
           // parsing JSON
            json = new JSONArray(retSrc); //Convert String to JSON Object
        }


    } catch (UnsupportedEncodingException e) {
        e.printStackTrace();
    } catch (ClientProtocolException e) {
        e.printStackTrace();
    } catch (IOException e) {
        e.printStackTrace();
    }


    // return JSON String
    return json;

}

Answer 2

您也可以使用：

final String result = EntityUtils.toString(httpEntity);

而不是：

json = sb.toString();

Answer 3

我的预感是charset错了，JSON通常应该在UTF-8中，请尝试：

BufferedReader reader = new BufferedReader(new InputStreamReader(is, "UTF-8"), 1024);

同时将缓冲区大小从8增加到1024.

在android中实现Json时出错

3 个答案: