“主要” java.lang.NoClassDefFoundError：org / apache / http / HttpEntity

Question

I'm trying to use the apache http library in my project. I imported the libreries in my project http://imgur.com/WvwqcDS

When I run my program, I get this error:

Exception in thread "main" java.lang.NoClassDefFoundError: org/apache/http/HttpEntity
        at java.lang.Class.getDeclaredMethods0(Native Method)
        at java.lang.Class.privateGetDeclaredMethods(Unknown Source)
        at java.lang.Class.getMethod0(Unknown Source)
        at java.lang.Class.getMethod(Unknown Source)
        at sun.launcher.LauncherHelper.getMainMethod(Unknown Source)
        at sun.launcher.LauncherHelper.checkAndLoadMain(Unknown Source)
Caused by: java.lang.ClassNotFoundException: org.apache.http.HttpEntity
        at java.net.URLClassLoader$1.run(Unknown Source)
        at java.net.URLClassLoader$1.run(Unknown Source)
        at java.security.AccessController.doPrivileged(Native Method)
        at java.net.URLClassLoader.findClass(Unknown Source)
        at java.lang.ClassLoader.loadClass(Unknown Source)
        at sun.misc.Launcher$AppClassLoader.loadClass(Unknown Source)
        at java.lang.ClassLoader.loadClass(Unknown Source)
        ... 6 more

Answer 1

The ClassLoader can't find org.apache.http.HttpEntity, which should be inside "httpcore-4.3.jar". Open the jar as an archive and verify that it contains org/apache/http/HttpEntity.class. If it does, the issue is in your launch configuration. In Eclipse, go to Run > Run Configurations... and find the Java Application profile for your main class (which should be the class containing the main method in "Launcher" project, based on the screenshot). Under the Classpath tab, you should see your library jars listed.

If not, go back to your "Launcher" project in the Navigation pane, right-click and select Properties, go to "Build Path", remove your jars, press OK, then go back in and add them again (to guarantee the eclipse meta-data is fresh). Also, under the "Order and Export" tab, it's a good idea to check off all jars so that if you include Launcher as a dependency for another project, the jars are transitively included.

Answer 2

您的Eclipse在查找外部jar时遇到麻烦，请尝试将其导入到您的工作区中，或者使用“添加外部jar”将它们引用到外部

Answer 3

In my case Maven was not updating dependencies properly. I use mvn clean and then re-updated dependencies then it got fixed.