发出发布请求引发nullpointerexception

Question

我试图从我的一个android应用程序发出发布请求，但是由于HttpClient.execute某种原因该方法出错。

在我的应用程序中，我有一个makePostRequest方法，用于发出发布请求。方法如下：

// Makes a post request to the server
public void makePostRequest(String url, ArrayList<NameValuePair> postData) {
    HttpClient client = new DefaultHttpClient();
    HttpPost postRequest = new HttpPost();

    try {
        boolean prnull = postRequest == null;
        Log.d("DEBUG:", String.valueOf(prnull));
        postRequest.setEntity(new UrlEncodedFormEntity(postData));
        HttpResponse response = client.execute(postRequest);
        Log.i("INFO:", response.toString());
    } catch (ClientProtocolException e) {
        Log.d("DEBUG:", e.toString());
    } catch (IOException e) {
        Log.d("DEBUG:", e.toString());
    }

}

在活动中，我将其用作：

    // Process user registration
    Button registerButton = (Button) findViewById(R.id.registerButton);
    registerButton.setOnClickListener(new View.OnClickListener() {

        @Override
        public void onClick(View v) {
            ArrayList<NameValuePair> postData = new ArrayList<NameValuePair>(2);
            postData.add(new BasicNameValuePair("email", "testemail@gmail.com"));
            postData.add(new BasicNameValuePair("password", "abcdxyz"));
            makePostRequest(register_url, postData);
        }
    });

以下是堆栈跟踪：

05-13 06:12:55.888: E/AndroidRuntime(21553): FATAL EXCEPTION: main
05-13 06:12:55.888: E/AndroidRuntime(21553): Process: com.example.unishots, PID: 21553
05-13 06:12:55.888: E/AndroidRuntime(21553): java.lang.NullPointerException
05-13 06:12:55.888: E/AndroidRuntime(21553):    at org.apache.http.impl.client.AbstractHttpClient.determineTarget(AbstractHttpClient.java:496)
05-13 06:12:55.888: E/AndroidRuntime(21553):    at org.apache.http.impl.client.AbstractHttpClient.execute(AbstractHttpClient.java:487)
05-13 06:12:55.888: E/AndroidRuntime(21553):    at org.apache.http.impl.client.AbstractHttpClient.execute(AbstractHttpClient.java:465)
05-13 06:12:55.888: E/AndroidRuntime(21553):    at com.example.unishots.ShotsActivity.makePostRequest(ShotsActivity.java:61)
05-13 06:12:55.888: E/AndroidRuntime(21553):    at com.example.unishots.RegisterActivity$2.onClick(RegisterActivity.java:42)
05-13 06:12:55.888: E/AndroidRuntime(21553):    at android.view.View.performClick(View.java:4633)
05-13 06:12:55.888: E/AndroidRuntime(21553):    at android.view.View$PerformClick.run(View.java:19330)
05-13 06:12:55.888: E/AndroidRuntime(21553):    at android.os.Handler.handleCallback(Handler.java:733)
05-13 06:12:55.888: E/AndroidRuntime(21553):    at android.os.Handler.dispatchMessage(Handler.java:95)
05-13 06:12:55.888: E/AndroidRuntime(21553):    at android.os.Looper.loop(Looper.java:157)
05-13 06:12:55.888: E/AndroidRuntime(21553):    at android.app.ActivityThread.main(ActivityThread.java:5356)
05-13 06:12:55.888: E/AndroidRuntime(21553):    at java.lang.reflect.Method.invokeNative(Native Method)
05-13 06:12:55.888: E/AndroidRuntime(21553):    at java.lang.reflect.Method.invoke(Method.java:515)
05-13 06:12:55.888: E/AndroidRuntime(21553):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1265)
05-13 06:12:55.888: E/AndroidRuntime(21553):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1081)
05-13 06:12:55.888: E/AndroidRuntime(21553):    at dalvik.system.NativeStart.main(Native Method)

我已经检查了它postRequest是否不为null，因为这是传递给execute方法的唯一参数。在这里可能出什么问题了？

更新

在扩展的ShotsActivity类中，URL被定义为String变量RegisterActivity。网址定义如下：

// Server url variables
public String base_url = "http://192.168.2.8:8000";
public String login_url = base_url + "/login/";
public String register_url = base_url + "/api/v1/users";

Answer 1

我认为问题在于，尽管您将String url传递给makePostRequest（），但您并未在任何地方使用它。也许您应该将其传递给HttpPost（url）