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java.lang.ClassNotFoundException when running java -jar

由 女生的网名这么多〃 提交于 2019-12-04 13:49:01
VonC
Could not find the main class: MyClass

The error seems actually related to your MANIFEST which:

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

The best solution when you have a jar is to try to include the required jars into the manifest declaration.

Manifest-Version: 1.0 
Class-Path:  
 customer_client.jar  
 mailer_client.jar  
 signon_client.jar
  • or may not define adequately the MainClass within your 'my_jar.jar'.

See this HowTo:

<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>

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

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.

You need to specify all the other jars that are required in your classpath in the manifest file before you can execute java -jar my-test.jar, here is a copy of one of my manifest files. With all these entries in the manifest I can specify java -jar db_field_cleaner.jar and all the other jars are inlined into the classpath :

Manifest-Version: 1.0
Archiver-Version: Plexus Archiver
Created-By: Apache Maven
Built-By: James B
Build-Jdk: 1.6.0_01
Package: com.blah.dbfieldcleaner
Specification-Title: db_field_cleaner
Specification-Version: 2.5.7-SNAPSHOT
Implementation-Title: db_field_cleaner
Implementation-Version: 2.5.7-SNAPSHOT
Implementation-Vendor-Id: com.blah.dbfieldcleaner
Implementation-Vendor:
Main-Class: com.blah.dbfieldcleaner.main.Main
mode: development
url: ..\..\db_field_cleaner\target\site
Class-Path: log4j-1.2.14.jar cygna_commons-2.5.7-SNAPSHOT.jar mail-1.4
 .jar activation-1.1.jar jdic-0.9.5.jar jdic_native-0.9.5.jar jdic_plu
 s-0.2.2.jar jdic_plus_native-0.2.2.jar jtds-1.2.2.jar xstream-1.3.1.j
 ar xpp3_min-1.1.4c.jar commons-net-2.0.jar text_processing-2.5.7-SNAP
 SHOT.jar

Alternatively, use Maven, it's loads better at this kind of stuff!

You had given answer yourself :-) add all the jars to your runtime classpath.As you said earlier *.jar solved one problem but loggers are not able to find out, so add log4j.jar to the path. Basically the idea is add all the jars required for running in to classpath.

The command line options for java can be found here.

The -jar and -cp/-classpath options are mutually exclusive. The -jar option requires the use of a manifest and the relative paths to dependencies should be listed in this file. But essentially, the manifest is an optional mechanism - you can specify the required information externally at bootstrap time. If the manifest is causing you problems, don't use one.

I would test that you have you have located all your dependencies with a command like this:

java -cp /usr/local/lib/libthrift.jar:my_jar.jar  MyClass

Note that the compiler may successfully compile your classes even if all the classes that might be required at runtime are not present. Compilation will succeed if the direct dependencies of your classes are present. The dependencies of your dependencies are not necessary to create the binary and the compiler will not inspect them needlessly.

The message about org/apache/log4j/Logger suggests that you have a missing dependency on log4j. It will be necessary to add this library to the classpath. Check the documentation for the Thrift library to determine its dependencies.

The class path references in the manifest file are relative refs. Just to debug, you might want to copy all the jars into the same location as my_jar.jar and attempt it again.

reference : http://www.rgagnon.com/javadetails/java-0587.html

You might try adding the jars to the domain of the server. I had a similar problem and this worked for me when I was running it on glassfish. I would get those not found exceptions. Eclipse recognized it and it compiled fine but when ran on the server it couldn't find the file. Try adding it to whatever lib directory the server is installed to.

This is the problem that is occurring,

if the JAR file was loaded from "C:\java\apps\appli.jar", and your manifest file has the Class-Path: reference "lib/other.jar", the class loader will look in "C:\java\apps\lib\" for "other.jar".  It won't look at the JAR file entry "lib/other.jar".

Solution:-

  1. Right click on project, Select Export.
  2. Select Java Folder and in it select Runnable JAR File instead of JAR file.
  3. Select the proper options and in the Library Handling section select the 3rd option i.e. (Copy required libraries into a sub-folder next to the generated JAR).
  4. Click finish and your JAR is created at the specified position along with a folder that contains the JARS mentioned in the manifest file.

  5. open the terminal,give the proper path to your jar and run it using this command java -jar abc.jar

    Now what will happen is the class loader will look in the correct folder for the referenced JARS since now they are present in the same folder that contains your app JAR..There is no "java.lang.NoClassDefFoundError" exception thrown now.

This worked for me... Hope it works you too!!!

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java
ant
build.xml
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