将 GWT SQL 示例部署到 AppEngine，在 DB 上记录错误

Question

我最近在 Google Cloud SQL 和 GWT 上学习了这个教程：http://code.google.com/apis/sql/docs/developers_guide_java.html

在必须创建 GuestbookExample.gwt.xml 文件后，我将此应用程序部署到我的谷歌云 sql 服务器。我认为我正确地创建了它：

  <!-- Inherit the default GWT style sheet.  You can change       -->
  <!-- the theme of your GWT application by uncommenting          -->
  <!-- any one of the following lines.                            -->
  <inherits name='com.google.gwt.user.theme.clean.Clean'/>
  <!-- <inherits name='com.google.gwt.user.theme.standard.Standard'/> -->
  <!-- <inherits name='com.google.gwt.user.theme.chrome.Chrome'/> -->
  <!-- <inherits name='com.google.gwt.user.theme.dark.Dark'/>     -->

  <!-- Other module inherits                                      -->

  <!-- Specify the app entry point class.                         -->

  <!-- Specify the paths for translatable code                    -->
  <source path='guestbook'/>

</module>

它能够部署到服务器，从 GWT 编译器编译没有问题。

当我尝试访问链接到我的项目的 apppot 站点时，我收到 HTTP 错误：

Error: Server Error
The server encountered an error and could not complete your request.

If the problem persists, please report your problem and mention this error message and the query that caused it.

我觉得这很奇怪，所以我检查了 Google Cloud SQL 数据库上的日志，发现错误如下：

[02/Dec/2011:11:25:36 -0800] "GET / HTTP/1.1" 500 0 - "Mozilla/5.0 (Windows NT 6.1; WOW64; rv:8.0) Gecko/20100101 Firefox/8.0" "cst433t1proj.appspot.com" ms=109 cpu_ms=175 api_cpu_ms=0 cpm_usd=0.004894 instance=00c61b117cb6def6096f8754a01131e49502

C 2011-12-02 11:25:36.913

Uncaught exception from servlet
java.lang.UnsupportedClassVersionError: guestbook/GuestbookServlet : Unsupported major.minor version 51.0
    at com.google.appengine.runtime.Request.process-0000000000000000(Request.java)
    at java.lang.ClassLoader.defineClass1(Native Method)
    at java.lang.ClassLoader.defineClass(ClassLoader.java:634)
    at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:142)
    at java.net.URLClassLoader.defineClass(URLClassLoader.java:277)
    at sun.reflect.GeneratedMethodAccessor5.invoke(Unknown Source)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:616)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:266)
    at org.mortbay.util.Loader.loadClass(Loader.java:91)
    at org.mortbay.util.Loader.loadClass(Loader.java:71)
    at org.mortbay.jetty.servlet.Holder.doStart(Holder.java:73)
    at org.mortbay.jetty.servlet.ServletHolder.doStart(ServletHolder.java:242)
    at org.mortbay.component.AbstractLifeCycle.start(AbstractLifeCycle.java:50)
    at org.mortbay.jetty.servlet.ServletHandler.initialize(ServletHandler.java:685)
    at org.mortbay.jetty.servlet.Context.startContext(Context.java:140)
    at org.mortbay.jetty.webapp.WebAppContext.startContext(WebAppContext.java:1250)
    at org.mortbay.jetty.handler.ContextHandler.doStart(ContextHandler.java:517)
    at org.mortbay.jetty.webapp.WebAppContext.doStart(WebAppContext.java:467)
    at org.mortbay.component.AbstractLifeCycle.start(AbstractLifeCycle.java:50)
    at com.google.tracing.TraceContext$TraceContextRunnable.runInContext(TraceContext.java:449)
    at com.google.tracing.TraceContext$TraceContextRunnable$1.run(TraceContext.java:455)
    at com.google.tracing.TraceContext.runInContext(TraceContext.java:695)
    at com.google.tracing.TraceContext$AbstractTraceContextCallback.runInInheritedContextNoUnref(TraceContext.java:333)
    at com.google.tracing.TraceContext$AbstractTraceContextCallback.runInInheritedContext(TraceContext.java:325)
    at com.google.tracing.TraceContext$TraceContextRunnable.run(TraceContext.java:453)
    at java.lang.Thread.run(Thread.java:679)

我可以做些什么来解决这个错误？我是这个数据库的新手。我刚刚学习 GWT 以协助创建最终项目。任何帮助将不胜感激。

Answer 1

您可能正在使用 Java 7？ GAE 支持特定版本的 Java 检查 http://code.google.com/appengine/docs/java/overview.html 并查看您是否使用了不受支持的版本。