GAE错误：java.lang.RuntimeException: Unable to locate the App Engine agent.

错误：

java.lang.RuntimeException: Unable to locate the App Engine agent. Please use dev_appserver, KickStart,  or set the jvm flag: "-javaagent:<sdk_root>/lib/agent/appengine-agent.jar"
 at com.google.appengine.tools.development.DevAppServerFactory.testAgentIsInstalled(DevAppServerFactory.java:102)
 at com.google.appengine.tools.development.DevAppServerFactory.createDevAppServer(DevAppServerFactory.java:77)
 at com.google.appengine.tools.development.DevAppServerFactory.createDevAppServer(DevAppServerFactory.java:38)
 at com.google.appengine.tools.development.DevAppServerMain$StartAction.apply(DevAppServerMain.java:153)
 at com.google.appengine.tools.util.Parser$ParseResult.applyArgs(Parser.java:48)
 at com.google.appengine.tools.development.DevAppServerMain.<init>(DevAppServerMain.java:113)
 at com.google.appengine.tools.development.DevAppServerMain.main(DevAppServerMain.java:89)
Caused by: java.lang.NoClassDefFoundError: com/google/appengine/tools/development/agent/AppEngineDevAgent
 at com.google.appengine.tools.development.DevAppServerFactory.testAgentIsInstalled(DevAppServerFactory.java:98)
 ... 6 more
Caused by: java.lang.ClassNotFoundException: com.google.appengine.tools.development.agent.AppEngineDevAgent
 at java.net.URLClassLoader$1.run(URLClassLoader.java:200)
 at java.security.AccessController.doPrivileged(Native Method)
 at java.net.URLClassLoader.findClass(URLClassLoader.java:188)
 at java.lang.ClassLoader.loadClass(ClassLoader.java:307)
 at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:301)
 at java.lang.ClassLoader.loadClass(ClassLoader.java:252)
 at java.lang.ClassLoader.loadClassInternal(ClassLoader.java:320)
 ... 7 more
解决方法

-javaagent:D:\OpenSourse\appengine-java-sdk-1.2.6\appengine-java-sdk-1.2.6\lib\agent\appengine-agent.jar