运行java -jar时的java.lang.ClassNotFoundException

问题描述

我正在使用ant构建我的 build.xml 文件，它编译好了，但后来获得运行时 java.lang.NoClassDefFoundError 通过 java -jar my_jar.jar 运行生成的jar时。看起来好像很多，但没有一个相关问题的解决方案适合我。

I'm using ant to build my build.xml file, it compiles ok, but then getting a runtime java.lang.NoClassDefFoundError when running the resulting jar via "java -jar my_jar.jar". It seems like this comes up a lot but none of the related questions' solutions worked for me.

我的 javac 仅包含 /usr/local/lib/libthrift.jar ，主 .java 文件导入a一堆thrift包，例如 org.apache.thrift.transport.TTransportException 。

My classpath for javac contains only "/usr/local/lib/libthrift.jar" and the main .java file imports a bunch of thrift packages such as org.apache.thrift.transport.TTransportException.

当我尝试运行程序时通过：

When I try running the program via:

java -jar MyClass.jar

，我收到错误：

Exception in thread "main" **java.lang.NoClassDefFoundError**: org/apache/thrift/transport/TTransportException
Caused by: java.lang.ClassNotFoundException: org.apache.thrift.transport.TTransportException
        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)
Could not find the main class: **MyClass**. Program will exit.

以下是我到目前为止尝试过的不起作用的事情：

Here are the things I've tried so far that don't work:

• 在命令行中添加一个标志，如java -cp / usr / local / lib / libthrift。 jar -jar my_jar.jar ，结果与上面的错误相同

• adding a flag on the command line like "java -cp /usr/local/lib/libthrift.jar -jar my_jar.jar", the result is the same error as above

添加 & lt; attribute name =Class-Pathvalue =./：/ usr / local / lib / libthrift.jar/> 在我的jar的清单> 标记内，结果与上面的错误相同

adding <attribute name="Class-Path" value="./:/usr/local/lib/libthrift.jar"/> inside my jar's manifest> tag, the result is the same error as above

将 -Xbootclasspath / a：/usr/local/lib/libthrift.jar：./ 添加到java命令线。它解决了第一个错误，但出现了另一个错误：

adding -Xbootclasspath/a:/usr/local/lib/libthrift.jar:./ to the java command line. it solves the first error but a different error comes up:

线程main中的异常java.lang.NoClassDefFoundError：org / apache / log4j / Logger
at org.apache.thrift.transport.TServerSocket。< clinit>（TServerSocket.java:36）
at MyClass.start（Unknown Source）
at MyClass.main（Unknown Source）

Exception in thread "main" java.lang.NoClassDefFoundError: org/apache/log4j/Logger at org.apache.thrift.transport.TServerSocket.<clinit>(TServerSocket.java:36) at MyClass.start(Unknown Source) at MyClass.main(Unknown Source)

编辑：

如果我发表评论在实例化缺失类但保留导入的代码中，代码执行正常。

If I comment out the code that instantiates the missing classes but leave the imports, the code executes fine.

编辑：

我将我的java类移动到服务器并使用manifest属性中的服务器引用MainClass，但是没有修复任何内容。

I moved my java classes to a server and referenced the MainClass with the server in the manifest attribute, but that didn't fix anything.

推荐答案

Could not find the main class: MyClass

该错误实际上与您的 MANIFEST 有关：

The error seems actually related to your MANIFEST which:

• 可能没有完整的类路径 Class-Path ：请参阅

• may not have a complete classpath Class-Path: see this HowTo





Manifest-Version: 1.0
Class-Path:
 customer_client.jar
 mailer_client.jar
 signon_client.jar





• 或者可能没有充分定义'my_jar.jar'中的MainClass。



参见：

<target name="jar" depends="compile">
     <delete file="hello.jar"/>
     <delete file="MANIFEST.MF"/>
     <manifest file="MANIFEST.MF">
        <attribute name="Built-By" value="${user.name}"/>
        <attribute name="Main-Class" value="howto.Hello"/>
    </manifest>

      <jar destfile="hello.jar"
           basedir="."
           includes="**/*.class"
           manifest="MANIFEST.MF"
           />
  </target>

< attribute name =Main-Classvalue =howto .Hello/> 需要指定 MainClass 的完整路径（包），而不仅仅是 MainClass 。

the <attribute name="Main-Class" value="howto.Hello"/> needs to specify the full path (packages) of the MainClass, not just MainClass.

如果你的主类在默认包中（），我不确定加载程序是否可以引用它（请参阅）

所以将 JarRunner 移动到一个包中，并在< attribute name =Main中正确声明它-Classvalue =myPackage.JarRunner/> 元素。

If your main class is in the default package (the unnamed package), I am not sure it can be referenced by the loader (see this SO question)
So move your JarRunner into a package, and declare it appropriately in the <attribute name="Main-Class" value="myPackage.JarRunner"/> element.

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