Java Appengine SDK 1.9.6 Method not found - google-app-engine

Question

I have been having a terrible time figuring out a method not found problem. I've found similar questions on the appengine google group but none of the answers have helped solve the problem. Running my war locally with the dev server works fine but when I deploy my app I get the error below. I've included the top of the exception, the top of the last caused by and a list of the jars in my war's lib folder.
Here is the top part of the exception. I put each agurment on it's own line to make it easier to read
java.lang.NoSuchMethodError: com.google.appengine.api.datastore.Key.<init>(
Ljava/lang/String;
Lcom/google/appengine/api/datastore/Key;
Ljava/lang/String;
Lcom/google/appengine/api/datastore/AppIdNamespace;)V
Here is the top of the last caused by.
Caused by: java.lang.NoSuchMethodError: com.google.appengine.api.datastore.Key.<init>(
Ljava/lang/String
;Lcom/google/appengine/api/datastore/Key;
Ljava/lang/String;
Lcom/google/appengine/api/datastore/AppIdNamespace;)V
at com.google.appengine.api.datastore.KeyFactory.createKey(KeyFactory.java:84)
at com.google.appengine.api.datastore.KeyFactory.createKey(KeyFactory.java:77)
at com.googlecode.objectify.Key.<init>(Key.java:97)
Here is a listing of the jars in my war's WEB-INF/lib folder.
aopalliance-1.0.jar
appengine-api-1.0-sdk-1.9.6.jar
appengine-api-labs-1.9.6.jar
appengine-jsr107cache-1.9.6.jar
asm-3.1.jar
cglib-2.2.1-v20090111.jar
client-only-0.1.jar
datanucleus-appengine-1.0.10.final.jar
datanucleus-core-1.1.5.jar
datanucleus-jpa-1.1.5.jar
geronimo-jpa_3.0_spec-1.1.1.jar
geronimo-jta_1.1_spec-1.1.1.jar
gin-1.5.0.jar
guava-15.0.jar
guava-gwt-15.0.jar
guice-3.0.jar
guice-assistedinject-3.0.jar
guice-multibindings-3.0.jar
guice-servlet-3.0.jar
gwt-servlet.jar
hibernate-validator-4.1.0.Final-sources.jar
hibernate-validator-4.1.0.Final.jar
hibernate-validator-annotation-processor-4.1.0.Final.jar
javax.inject-1.jar
jdo2-api-2.3-eb.jar
jsr107cache-1.1.jar
jsr173-1.0.jar
jsr305-1.3.9.jar
jta-1.1.jar
libservice.jar
log4j-over-slf4j-1.6.1.jar
mgwt-1.2.0-rc-opera-removed.jar
objectify-5.0.2.jar
persistence-api-1.0.jar
server-and-client-0.1.jar
server-only.jar
slf4j-api-1.7.2.jar
uadetector-core-0.9.2.jar
uadetector-resources-2013.02.jar
validation-api-1.0.0.GA-sources.jar
validation-api-1.0.0.GA.jar

Answer 1

This was happening because of a quirk of gradle and javac with a little help from GWT and Objectify.
Since ~version 4.1, Objectify has had a separate jar with some appengine java sources in it so that Objectify classes can be used in the browser via GWT.
By default, sources included in compile dependencies in gradle will included in the compile output of the compile task. This is because gradle does not use the sourcepath parameter to the java compiler and according to Oracle's javac documentation:
If the -sourcepath option is not specified, the user class path is
also searched for source files.
I fixed the problem by adding this to my gradle file
compileJava.options.compilerArgs += "-sourcepath"
compileJava.options.compilerArgs += ""