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I am creating an Android app using Google App Engine. In order to use GCM (Google Cloud Messaging), I have created a GCM module in Android Studio. This module provides a sample code that registers devices in the Datastore.

All was working well yesterday, and although nothing changed, I have this error when I try to register my device :

java.lang.NoSuchMethodError: com.google.appengine.api.datastore.Cursor: method <init>()V not found

I don't know what exactly means the notation <init>()V, but I found the Cursor class to be generated by the Google plugin of Android Studio, here :

enter image description here

This is the decompiled code inside Cursor.class :

// // Source code recreated from a .class file by IntelliJ IDEA // (powered by Fernflower decompiler) // package com.google.appengine.api.datastore; import java.io.Serializable; public final class Cursor implements Serializable { private String webString; public Cursor(String webString) { this.webString = webString; } public String toWebSafeString() { return this.webString; } public static Cursor fromWebSafeString(String encodedCursor) { if(encodedCursor == null) { throw new NullPointerException("encodedCursor must not be null"); } else { return new Cursor(encodedCursor); } } public boolean equals(Object o) { if(this == o) { return true; } else if(o != null && this.getClass() == o.getClass()) { Cursor cursor = (Cursor)o; return this.webString.equals(cursor.webString); } else { return false; } } public int hashCode() { return this.webString.hashCode(); } public String toString() { return this.webString; } }

Finally, this is my build.gradle :

// If you would like more information on the gradle-appengine-plugin please refer to the github page // https://github.com/GoogleCloudPlatform/gradle-appengine-plugin buildscript { repositories { jcenter() } dependencies { classpath 'com.google.appengine:gradle-appengine-plugin:1.9.18' } } repositories { jcenter(); } apply plugin: 'java' apply plugin: 'war' apply plugin: 'appengine' sourceCompatibility = 1.7 targetCompatibility = 1.7 dependencies { appengineSdk 'com.google.appengine:appengine-java-sdk:1.9.18' compile 'com.google.appengine:appengine-endpoints:1.9.18' compile 'com.google.appengine:appengine-endpoints-deps:1.9.18' compile 'javax.servlet:servlet-api:2.5' compile 'com.googlecode.objectify:objectify:4.0b3' compile 'com.ganyo:gcm-server:1.0.2' } appengine { downloadSdk = true appcfg { oauth2 = true } endpoints { getClientLibsOnBuild = true getDiscoveryDocsOnBuild = true } }

Because I changed nothing in the concerned code, I really can't understand what happened and I found nothing useful on the web.

Thank you in advance for your help.

Edit : StackTrace from the backend log

enter image description here

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It's looking for the empty constructor : method init()v not found

It appears this could be because Cursor.java is pulled from your <module>/build/classes/main (or <module>/build/exploded-app/WEB-INF/classes/main), when really it should just be pulled in from a library appengine-api-1.0-sdk-<version>.jar.

Have you added the source for a Cursor.java into your project src folder somehow? The App Engine build creates a runnable build at <module>/build/exploded-app and the cursor class is usually sourced from <module>/build/exploded-app/WEB-INF/lib/appengine-api-1.0-sdk-<version>.jar

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5 Comments

In fact, the App Engine module used to generate the class Cursor as you can see in my post. However, when I looked the real class inside the SDK, it was a totally different code (with the constructor). I tried to remove the generated class and to build the project, but everytime it was re-generated. The only solution I found was to update to the new SDK 1.9.20. Not the class is not generated anymore, but I still don't understand this behaviour. Thank you for your comment.
That's very strange, it does not do that for my installation using 1.9.18.
Yes, I haven't found any similar issue. I assume this is a configuration problem, or a conflict problem, as I work with shared sources.
If it's not too much trouble, can you try with a clean build and 1.9.18? Usually something like ./gradlew clean assemble or maybe just delete the <module>/build directory and try again? I suspect that the Cursor class ended up in there some how and was never cleaned out.
Before updating to 1.9.20 i've tried your two solutions. That's why I choosed the "radical" solution. :)

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