我正在开发一个简单的应用程序，我需要从本地主机sql数据库获取数据，当我在浏览器上测试时我能够获取JSON，但是我在检查android时遇到空指针异常，我已经交叉检查了IP地址，甚至尝试了异步任务，甚至在manifest.xml中声明了互联网权限，我调试了应用程序，但仍然无法找出错误的原因。
MainActivity.java
package library.danaraddi.com.myapplication;
import android.os.Bundle;
import android.support.v7.app.ActionBarActivity;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;
import android.widget.Toast;
import org.apache.http.NameValuePair;
import org.apache.http.message.BasicNameValuePair;
import org.json.JSONException;
import org.json.JSONObject;
import java.util.ArrayList;
import java.util.List;
public class MainActivity extends ActionBarActivity {
// views import
Button PostButton, GetButton;
TextView UsernameTextView, PasswordTextView;
EditText UsernameEditText, PasswordEditText;
// 192.168.1.210
// static fields
private static String URL = "http://192.168.1.210/cpsscripts/total_items.php";
private static String GET_TOTAL = "gettotal";
// objetcs
JSONParser jsonParser ;
List<NameValuePair> params;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
// Views Import
PostButton = (Button) findViewById(R.id.post_button);
GetButton = (Button) findViewById(R.id.get_button);
UsernameEditText = (EditText) findViewById(R.id.username_edittext);
PasswordEditText = (EditText) findViewById(R.id.password_edittext);
UsernameTextView = (TextView) findViewById(R.id.username_textView);
PasswordTextView = (TextView) findViewById(R.id.password_textView);
// Objects
jsonParser = new JSONParser();
params = new ArrayList<NameValuePair>();
params.add(new BasicNameValuePair("", ""));
PostButton.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
try {
JSONObject json = jsonParser.getJSONFromURL(URL, params);
String res = json.getString("gettotal");
UsernameTextView.setText(res);
} catch (JSONException e) {
e.printStackTrace();
}
}
});
}
}
JSONParser.java
package library.danaraddi.com.myapplication;
import android.util.Log;
import org.apache.http.HttpEntity;
import org.apache.http.HttpResponse;
import org.apache.http.NameValuePair;
import org.apache.http.client.ClientProtocolException;
import org.apache.http.client.entity.UrlEncodedFormEntity;
import org.apache.http.client.methods.HttpPost;
import org.apache.http.impl.client.DefaultHttpClient;
import org.json.JSONException;
import org.json.JSONObject;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.UnsupportedEncodingException;
import java.util.List;
/**
* Created by VINAY on 2/4/2015.
*/
public class JSONParser {
InputStream inputStream = null;
JSONObject jsonObject = null;
String output = "";
public JSONParser() {
}
public JSONObject getJSONFromURL(String URL, List<NameValuePair> valuePairs) {
try {
DefaultHttpClient httpClient = new DefaultHttpClient();
HttpPost httpPost = new HttpPost(URL);
httpPost.setEntity(new UrlEncodedFormEntity(valuePairs));
HttpResponse httpResponse = httpClient.execute(httpPost);
HttpEntity httpEntity = httpResponse.getEntity();
inputStream = httpEntity.getContent();
} catch (UnsupportedEncodingException e) {
e.printStackTrace();
} catch (ClientProtocolException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
try {
BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(inputStream,"iso-8859-1"),8);
StringBuilder stringBuilder = new StringBuilder();
String line = null;
while ((line = bufferedReader.readLine())!= null){
stringBuilder.append(line + "\n");
}
inputStream.close();
output = stringBuilder.toString();
Log.i("VINAY",output);
} catch (UnsupportedEncodingException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
try {
jsonObject = new JSONObject(output);
} catch (JSONException e) {
e.printStackTrace();
}
return jsonObject;
}
}
total_items.php
<?php
$response = array();
// import db connection variables
require_once __DIR__ . '/db_config.php';
// connect DB
$db= new mysqli(DB_SERVER, DB_USER, DB_PASSWORD,DB_DATABASE);
//if(!empty($_POST['total'])){
// Query
$totalquery ="SELECT * FROM `questions` ORDER BY `id` DESC LIMIT 1";
// connecting to mysql
if ($db->query($totalquery) == TRUE) {
$rows = $db->query($totalquery);
// get array
$totalrows = $rows->fetch_assoc();
// repond the total amount
$response["gettotal"] = $totalrows["id"];
// show response
print(json_encode($response));
} else {
echo "Error: " . $insertQuery . "<br>" . $db->error;
}
$db->close();
//}
?>
日志猫
02-05 06:01:24.248 400-400/library.danaraddi.com.myapplication E/AndroidRuntime﹕ FATAL EXCEPTION: main
java.lang.NullPointerException
at java.io.Reader.<init>(Reader.java:65)
at java.io.InputStreamReader.<init>(InputStreamReader.java:79)
at library.danaraddi.com.myapplication.JSONParser.getJSONFromURL(JSONParser.java:56)
at library.danaraddi.com.myapplication.MainActivity$1.onClick(MainActivity.java:64)
at android.view.View.performClick(View.java:2485)
at android.view.View$PerformClick.run(View.java:9080)
at android.os.Handler.handleCallback(Handler.java:587)
at android.os.Handler.dispatchMessage(Handler.java:92)
at android.os.Looper.loop(Looper.java:130)
at android.app.ActivityThread.main(ActivityThread.java:3683)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:507)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:839)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:597)
at dalvik.system.NativeStart.main(Native Method)
最佳答案
尝试在 JsonParser 的第 56 行使用它
BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(inputStream, "utf-8"));
并再次检查 list 中的互联网权限。
我是 Linux 新手，所以不确定这是否是明确的答案，但是查看/var/www/html 的权限表明只有用户 root 具有读写执行权限。由于我只是作为标准用户使用浏览器并且没有访问权限，因此我认为“其他”需要一些权限，所以我这样做了:
sudo chmod 755 html -R
现在我可以在浏览器中访问本地主机了。
我发现这个有关“Linux 中的用户、组和权限”的视频非常有帮助:
关于java - 无法从远程数据库获取数据，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/28337815/