当我运行Java应用程序时,我得到了一个NoClassDefFoundError。造成这种情况的典型原因是什么?


当前回答

如果有人因为java.lang.NoClassDefFoundError: org/apache/log4j/Logger错误来到这里,在我的例子中,它是因为我使用了log4j 2(但我没有添加它附带的所有文件),而一些依赖库使用了log4j 1。解决方案是添加Log4j 1。X桥:log4j-1.2-api-<version>.jar,随log4j 2而来。更多信息在log4j 2迁移中。

其他回答

此错误可能是由未检查的Java版本要求引起的。

在我的案例中,当我构建一个备受瞩目的开源项目时,通过使用SDKMAN从Java 9切换到Java 8,我能够解决这个错误。

sdk list java
sdk install java 8u152-zulu
sdk use java 8u152-zulu

然后按照下面的描述进行干净安装。


在使用Maven作为构建工具时,在禁用测试的情况下进行干净的“安装”构建有时是有帮助的,而且通常是令人满意的。

mvn clean install -DskipTests

现在已经构建并安装了所有内容,您可以继续运行测试。

mvn test

更新[https://www.infoq.com/articles/single-file-execution-java11/]:

在Java SE 11中,可以选择启动单个源代码文件 直接,不需要中间编译。为了方便大家, 所以像你这样的新手不需要运行javac + Java(当然, 让他们感到困惑)。

如果有人因为java.lang.NoClassDefFoundError: org/apache/log4j/Logger错误来到这里,在我的例子中,它是因为我使用了log4j 2(但我没有添加它附带的所有文件),而一些依赖库使用了log4j 1。解决方案是添加Log4j 1。X桥:log4j-1.2-api-<version>.jar,随log4j 2而来。更多信息在log4j 2迁移中。

虽然这可能是由于编译时和运行时之间的类路径不匹配造成的,但这并不一定是真的。

在这种情况下,记住两到三个不同的异常是很重要的:

java.lang.ClassNotFoundException This exception indicates that the class was not found on the classpath. This indicates that we were trying to load the class definition, and the class did not exist on the classpath. java.lang.NoClassDefFoundError This exception indicates that the JVM looked in its internal class definition data structure for the definition of a class and did not find it. This is different than saying that it could not be loaded from the classpath. Usually this indicates that we previously attempted to load a class from the classpath, but it failed for some reason - now we're trying to use the class again (and thus need to load it, since it failed last time), but we're not even going to try to load it, because we failed loading it earlier (and reasonably suspect that we would fail again). The earlier failure could be a ClassNotFoundException or an ExceptionInInitializerError (indicating a failure in the static initialization block) or any number of other problems. The point is, a NoClassDefFoundError is not necessarily a classpath problem.

我通过禁用所有模块的preDexLibraries来解决我的问题:

dexOptions {
        preDexLibraries false
        ...