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PORESTful request using HTTPUrlConnection
 

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    <p>I'm writing my first Android app, and trying to get the hang of making a REST call from within the app. Following a couple pages and other SO posts, I've got this:</p> <pre><code>URL serverUrl = new URL("http://localhost:13980/api/maps/"); //the value is hardcoded for testing purposes public String getMapsJson() { Log.d("Minimap", "&gt;&gt; getting maps json from " + serverUrl.toString()); String output = ""; HttpURLConnection connection = null; try { connection = (HttpURLConnection) serverUrl.openConnection(); connection.setRequestMethod("GET"); Log.d("Minimap", "connection opened!"); InputStream in = new BufferedInputStream(connection.getInputStream()); Log.d("Minimap", "input stream captured"); output = readStream(in); Log.d("Minimap", "stream read"); } catch (Exception e) { Log.d("Minimap", e.getMessage()); //************* This is line 53 &lt;&lt;&lt;&lt;&lt;&lt; } finally { connection.disconnect(); } Log.d("Minimap", "JSON: " + output); return output; } private String readStream(InputStream in) { try { BufferedReader reader = new BufferedReader(new InputStreamReader(in)); String line = reader.readLine(); String output = line; while((line = reader.readLine()) != null) output += line; return output; } catch (IOException e) { e.printStackTrace(); return ""; } } </code></pre> <p>The output I'm getting from logcat is just</p> <pre><code>11-19 07:38:31.599 3813-3813/com.northstar.minimap D/Minimap﹕ &gt;&gt; getting maps json from http://localhost:13980/api/maps/ 11-19 07:38:31.599 3813-3813/com.northstar.minimap D/Minimap﹕ connection opened! </code></pre> <p>and then the app crashes with the following stack trace:</p> <pre><code>11-19 08:02:50.903 744-744/com.northstar.minimap E/AndroidRuntime﹕ FATAL EXCEPTION: main java.lang.RuntimeException: Unable to start activity ComponentInfo{com.northstar.minimap/com.northstar.minimap.MapActivity}: java.lang.NullPointerException: println needs a message at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2180) at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2230) at android.app.ActivityThread.access$600(ActivityThread.java:141) at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1234) at android.os.Handler.dispatchMessage(Handler.java:99) at android.os.Looper.loop(Looper.java:137) at android.app.ActivityThread.main(ActivityThread.java:5041) at java.lang.reflect.Method.invokeNative(Native Method) at java.lang.reflect.Method.invoke(Method.java:511) at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560) at dalvik.system.NativeStart.main(Native Method) Caused by: java.lang.NullPointerException: println needs a message at android.util.Log.println_native(Native Method) at android.util.Log.d(Log.java:138) at com.northstar.minimap.Communicator.getMapsJson(Communicator.java:53) at com.northstar.minimap.MapActivity.onCreate(MapActivity.java:36) at android.app.Activity.performCreate(Activity.java:5104) at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1080) at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2144)             at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2230)             at android.app.ActivityThread.access$600(ActivityThread.java:141)             at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1234)             at android.os.Handler.dispatchMessage(Handler.java:99)             at android.os.Looper.loop(Looper.java:137)             at android.app.ActivityThread.main(ActivityThread.java:5041)             at java.lang.reflect.Method.invokeNative(Native Method)             at java.lang.reflect.Method.invoke(Method.java:511)             at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793)             at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560)             at dalvik.system.NativeStart.main(Native Method) 11-19 08:02:50.933 308-445/system_process W/ActivityManager﹕ Force finishing activity com.northstar.minimap/.MapActivity 11-19 08:02:50.943 308-445/system_process W/ActivityManager﹕ Force finishing activity com.northstar.minimap/.MainActivity </code></pre> <p>The page it's querying (<code>http://localhost:13980/api/maps/</code>) is a simple GET endpoint that spits back some JSON. At this point, I'd just be happy if the JSON it pulled was printed to LogCat.</p> <p>Thanks!</p>
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    1. COWhat do you mean by "crashes"? How do you know it is crashing and what is the stack trace of any exceptions that are thrown?
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    2. COThis does not solve your problem but improves exception handling: readStream should NOT catch the exception but specify it instead in its throws clause.
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    3. CO@JasonC The app exits on the emulator, which displays a notification that says "Unfortunately, Minimap has stopped." I've updated the description with the stack trace. Looks like it's happening at the Log.d() call in getMapsJson's catch block.
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