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在Google App Engine for Java中使用ClassNotFoundException

google-app-engine
5
我和一个朋友正在使用Java SDK涉足App Engine。我们成功地编写了一个“Hello, World”示例，但是当我们尝试添加代码并使用com.google.api.client.http中的类来调用一个简单的Web服务时，代码可以编译通过，但会引起运行时错误：
HTTP ERROR 500

Problem accessing /surreality. Reason:

   com/google/api/client/http/HttpTransport

Caused by:

HTTP ERROR 500

Problem accessing /surreality. Reason:

   com/google/api/client/http/javanet/NetHttpTransport

Caused by:

java.lang.NoClassDefFoundError: com/google/api/client/http/javanet/
NetHttpTransport
       at
com.surreality.scratch.SurrealityServlet.performSearch(SurrealityServlet.java:
31)
       at
com.surreality.scratch.SurrealityServlet.doGet(SurrealityServlet.java:
18)
       at javax.servlet.http.HttpServlet.service(HttpServlet.java:617)
       at javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
       at org.mortbay.jetty.servlet.ServletHolder.handle(ServletHolder.java:
511)

需要翻译的内容:

涉及代码如下:

package com.surreality.scratch;

import java.io.IOException;
import javax.servlet.http.*;
import java.util.List;
import com.google.api.client.googleapis.*;
import com.google.api.client.http.*;
import com.google.api.client.http.javanet.*;
import com.google.api.client.util.Key;

@SuppressWarnings("serial")
public class SurrealityServlet extends HttpServlet {

       public void doGet(HttpServletRequest req, HttpServletResponse resp)
                       throws IOException {
               resp.setContentType("text/plain");
               try {
                       this.performSearch(resp);
                       resp.getWriter().println("Here...");
               } catch (Exception e) {
                       resp.getWriter().println("Onoes!");
               }
       }

       public void performSearch(HttpServletResponse resp) throws Exception
{

               try {
                       resp.getWriter().println("Perform Search ....");
                       resp.getWriter().println("-------------------");

                       HttpTransport transport = new NetHttpTransport(); // This line
causes our servlet to implode on every request
               } catch (Exception e) {
                       resp.getWriter().println("failed");
                       throw e;
               }
       }
}

我们最好的猜测是构建类路径和运行时类路径之间存在差异，但我们的运行时类路径似乎没问题。 HttpTransport类在google-api-client-1.4.1-beta.jar库中，这个库被包含在Eclipse命令行生成要运行该项目的命令中。
/System/Library/Java/JavaVirtualMachines/1.6.0.jdk/Contents/Home/bin/
java -Ddatastore.default_high_rep_job_policy_unapplied_job_pct=50 -
Xmx512m -javaagent:/Applications/eclipse/plugins/
com.google.appengine.eclipse.sdkbundle_1.5.3.r37v201108301710/
appengine-java-sdk-1.5.3/lib/agent/appengine-agent.jar -
XstartOnFirstThread -Xbootclasspath/p:/Applications/eclipse/plugins/
com.google.appengine.eclipse.sdkbundle_1.5.3.r37v201108301710/
appengine-java-sdk-1.5.3/lib/override/appengine-dev-jdk-overrides.jar -
Dfile.encoding=MacRoman -classpath /Users/Arkaaito/Documents/AppEngine/
scratch/surreality/war/WEB-INF/classes:/Applications/eclipse/plugins/
com.google.appengine.eclipse.sdkbundle_1.5.3.r37v201108301710/
appengine-java-sdk-1.5.3/lib/shared/appengine-local-runtime-
shared.jar:/Applications/eclipse/plugins/
com.google.appengine.eclipse.sdkbundle_1.5.3.r37v201108301710/
appengine-java-sdk-1.5.3/lib/shared/el-api.jar:/Applications/eclipse/
plugins/com.google.appengine.eclipse.sdkbundle_1.5.3.r37v201108301710/
appengine-java-sdk-1.5.3/lib/shared/jsp/repackaged-appengine-
ant-1.7.1.jar:/Applications/eclipse/plugins/
com.google.appengine.eclipse.sdkbundle_1.5.3.r37v201108301710/
appengine-java-sdk-1.5.3/lib/shared/jsp/repackaged-appengine-ant-
launcher-1.7.1.jar:/Applications/eclipse/plugins/
com.google.appengine.eclipse.sdkbundle_1.5.3.r37v201108301710/
appengine-java-sdk-1.5.3/lib/shared/jsp/repackaged-appengine-
jasper-6.0.29.jar:/Applications/eclipse/plugins/
com.google.appengine.eclipse.sdkbundle_1.5.3.r37v201108301710/
appengine-java-sdk-1.5.3/lib/shared/jsp/repackaged-appengine-jasper-
el-6.0.29.jar:/Applications/eclipse/plugins/
com.google.appengine.eclipse.sdkbundle_1.5.3.r37v201108301710/
appengine-java-sdk-1.5.3/lib/shared/jsp/repackaged-appengine-tomcat-
juli-6.0.29.jar:/Applications/eclipse/plugins/
com.google.appengine.eclipse.sdkbundle_1.5.3.r37v201108301710/
appengine-java-sdk-1.5.3/lib/shared/jsp-api.jar:/Applications/eclipse/
plugins/com.google.appengine.eclipse.sdkbundle_1.5.3.r37v201108301710/
appengine-java-sdk-1.5.3/lib/shared/servlet-api.jar:/Applications/
eclipse/plugins/
com.google.appengine.eclipse.sdkbundle_1.5.3.r37v201108301710/
appengine-java-sdk-1.5.3/lib/user/appengine-api-1.0-sdk-1.5.3.jar:/
Applications/eclipse/plugins/
com.google.appengine.eclipse.sdkbundle_1.5.3.r37v201108301710/
appengine-java-sdk-1.5.3/lib/user/appengine-api-labs-1.5.3.jar:/
Applications/eclipse/plugins/
com.google.appengine.eclipse.sdkbundle_1.5.3.r37v201108301710/
appengine-java-sdk-1.5.3/lib/user/appengine-jsr107cache-1.5.3.jar:/
Applications/eclipse/plugins/
com.google.appengine.eclipse.sdkbundle_1.5.3.r37v201108301710/
appengine-java-sdk-1.5.3/lib/user/jsr107cache-1.1.jar:/Applications/
eclipse/plugins/
com.google.appengine.eclipse.sdkbundle_1.5.3.r37v201108301710/
appengine-java-sdk-1.5.3/lib/user/orm/datanucleus-
appengine-1.0.9.final.jar:/Applications/eclipse/plugins/
com.google.appengine.eclipse.sdkbundle_1.5.3.r37v201108301710/
appengine-java-sdk-1.5.3/lib/user/orm/datanucleus-core-1.1.5.jar:/
Applications/eclipse/plugins/
com.google.appengine.eclipse.sdkbundle_1.5.3.r37v201108301710/
appengine-java-sdk-1.5.3/lib/user/orm/datanucleus-jpa-1.1.5.jar:/
Applications/eclipse/plugins/
com.google.appengine.eclipse.sdkbundle_1.5.3.r37v201108301710/
appengine-java-sdk-1.5.3/lib/user/orm/geronimo-jpa_3.0_spec-1.1.1.jar:/
Applications/eclipse/plugins/
com.google.appengine.eclipse.sdkbundle_1.5.3.r37v201108301710/
appengine-java-sdk-1.5.3/lib/user/orm/geronimo-jta_1.1_spec-1.1.1.jar:/
Applications/eclipse/plugins/
com.google.appengine.eclipse.sdkbundle_1.5.3.r37v201108301710/
appengine-java-sdk-1.5.3/lib/user/orm/jdo2-api-2.3-eb.jar:/
Applications/eclipse/plugins/
com.google.appengine.eclipse.sdkbundle_1.5.3.r37v201108301710/
appengine-java-sdk-1.5.3/lib/appengine-tools-api.jar:/Users/Arkaaito/
Documents/AppEngine/scratch/surreality/war/WEB-INF/lib/google-api-java-
client-1.4.1-beta/dependencies/httpclient-4.0.3.jar:/Users/Arkaaito/
Documents/AppEngine/scratch/surreality/war/WEB-INF/lib/google-api-java-
client-1.4.1-beta/dependencies/httpcore-4.0.1.jar:/Users/Arkaaito/
Documents/AppEngine/scratch/surreality/war/WEB-INF/lib/google-api-java-
client-1.4.1-beta/google-api-client-1.4.1-beta.jar:/Users/Arkaaito/
Documents/AppEngine/scratch/surreality/war/WEB-INF/lib/google-api-java-
client-1.4.1-beta/google-api-client-googleapis-1.4.1-beta.jar:/Users/
Arkaaito/Documents/AppEngine/scratch/surreality/war/WEB-INF/lib/google-
api-java-client-1.4.1-beta/google-api-client-extensions-1.4.1-
beta.jar:/Users/Arkaaito/Documents/AppEngine/scratch/surreality/war/
WEB-INF/lib/google-api-java-client-1.4.1-beta/google-api-client-
googleapis-extensions-1.4.1-beta.jar:/Users/Arkaaito/Documents/
AppEngine/scratch/surreality/war/WEB-INF/lib/geronimo-
jpa_3.0_spec-1.1.1.jar:/Users/Arkaaito/Documents/AppEngine/scratch/
surreality/war/WEB-INF/lib/geronimo-jta_1.1_spec-1.1.1.jar
com.google.appengine.tools.development.DevAppServerMain --port=3333 /
Users/Arkaaito/Documents/AppEngine/scratch/surreality/war

有没有人遇到过这个问题，或者有没有建议我们应该如何进行调试？我相信这是一个简单的问题，可能是一个配置问题，但作为新手，除了查看类路径之外，我们不确定应该查看什么。

你需要在你的Web应用程序中打包一些API JAR文件吗？ - Paul Grime
JAR 文件已在类路径上 - 我需要做些什么才能将它们打包为必要的文件呢？ - Arkaaito
这些JAR文件可能需要复制到您的WEB-INF/lib文件夹中。您是使用Maven，还是手动下载这些JAR文件的？ - Paul Grime
我手动下载了它们。目前它们位于~/Documents/AppEngine/scratch/surreality/war/WEB-INF/lib/中 - 我已确认对于我认为相关的JAR（google-api-client-1.4.1-beta.jar），生成的命令行中的位置与文件的实际位置相匹配。 - Arkaaito
3个回答
5

在WEB-INF/lib目录下，您有一些子目录 google-api-java-client-1.4.1-beta 和 google-api-java-client-1.4.1-beta/dependencies，这些子目录中包含的JAR文件应该直接在WEB-INF/lib目录下。

哎呀！我本来就认为问题会是非常简单的，但我没想到它竟然如此之简单。谢谢！ - Arkaaito
@Arkaaito，你似乎混淆了运行应用程序引擎所需的配置和应用程序引擎运行你的应用程序。类路径是为了让应用程序引擎运行，不需要任何特定于你的应用程序的内容。设置应用程序访问其所有依赖项与标准servlet相同。 - Stephen Denne
3
0
如果您正在使用Google Cloud Engine和Eclipse：
将jar文件添加到Appengine项目中
  • 它必须位于目录/{Base Directory}/src/main/webapp/WEB-INF/lib下
  • 将jar文件复制到此目录中
  • 在Eclipse中->项目->构建路径->配置构建路径->库->添加外部JAR：转到/{Base Directory}/src/main/webapp/WEB-INF/lib并获取文件
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