为什么从 JAR 文件加载主类清单属性失败了？

我以这种方式创建了一个 JAR 文件 jar cf jar-file input-files。现在，我正在尝试运行它。运行它不起作用(找不到 jre 命令) :

jre -cp app.jar MainClass

这也行不通:

java -jar main.jar

(未能从 main.jar 加载 Main-Class 清单属性)。

我还发现

运行打包为 JAR 文件(版本1.2——需要 主类清单标头)

什么是“主类清单头”? 我如何创建它，我把它放在哪里？

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最佳答案

I'm not sure I believe your symptoms:

  • If the jre command isn't found, then running jre -cp app.jar should give the same error
  • Just adding a JAR file to the classpath shouldn't give the error you're seeing

I'd expect you to see this error if you run:

java -jar app.jar

The Main-Class header needs to be in the manifest for the JAR file - this is metadata about things like other required libraries. See the Sun documentation for how to create an appropriate manifest. Basically you need to create a text file which includes a line like this:

Main-Class: MainClass

Then run

jar cfm app.jar manifest.txt *.class
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You can run with:

java -cp .;app.jar package.MainClass

It works for me if there is no manifest in the JAR file.

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  1. set the classpath and compile

    javac -classpath "C:\Program Files\Java\jdk1.6.0_updateVersion\tools.jar" yourApp.java

  2. create manifest.txt

    Main-Class: yourApp newline

  3. create yourApp.jar

    jar cvf0m yourApp.jar manifest.txt yourApp.class

  4. run yourApp.jar

    java -jar yourApp.jar

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The easiest way to be sure that you have created the runnable JAR file correctly, with the appropriate manifest file, is to use Eclipse to build it for you. In your Eclipse project, you basically just select File/Export from the menu, and follow the prompts.

That way, you can be sure that your JAR file is correct and will know to look elsewhere if there is still an issue. The process is described in full in FAQ How do I create an executable JAR file for a stand-alone SWT program?.

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I got this error, and it was because I had the arguments in the wrong order:

CORRECT

java maui.main.Examples tagging -jar maui-1.0.jar

WRONG

java -jar maui-1.0.jar maui.main.Examples tagging
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I discovered that I was also having this error in NetBeans. I hope the following is helpful.

  1. Make sure that when you go to Project Configuration you set the main class you intend for running.
  2. Do a Build or Clean Build
  3. Place the jar file where you wish and try: java -jar "YourProject.jar" again at the command line.

This was the problem I was getting because I had other "test" programs I was using in NetBeans and I had to make sure the Main Class under the Run portion of the Project configuration was set correctly.

many blessings, John P

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I was getting the same error when i ran:
jar cvfm test.jar Test.class Manifest.txt

What resolved it was this:
jar cvfm test.jar Manifest.txt Test.class

My manifest has the entry point as given in oracle docs (make sure there is a new line character at the end of the file):
Main-Class: Test

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Try

java -cp .:mail-1.4.1.jar JavaxMailHTML

no need to have manifest file.

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I faced the same problem. This unix command is not able to find the main class. This is because the runtime and compile time JDK versions are different. Make the jar through eclipse after changing the java compiler version. The following link helped me.

http://crunchify.com/exception-in-thread-main-java-lang-unsupportedclassversionerror-comcrunchifymain-unsupported-major-minor-version-51-0/

Try running the jar created after this step and then execute it

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If your class path is fully specified in manifest, maybe you need the last version of java runtime environment. My problem fixed when i reinstalled the jre 8.

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If you using eclipse, try below: 1. Right click on the project -> select Export 2. Select Runnable Jar file in the select an export destination 3. Enter jar's name and Select "Package required ... " (second radio button) -> Finish

Hope this helps...!


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