摇篮& Groovy-错误:无法找到或加载主类 [英] Gradle & Groovy - Error: Could not find or load main class

问题描述

我可以使用gradle run运行我的项目，但是我不能使用java -jar运行jar文件.我使用以下示例项目重新创建了错误:链接到GitHub上的项目

I can run my project using gradle run, but I can't run the jar file using java -jar. I've recreated the error with this sample project: link to project on GitHub

这是通过gradlew

$ ./gradlew run

> Task :run
Hello world.

BUILD SUCCESSFUL in 4s

这是运行项目java -jar

$ ./gradlew build

BUILD SUCCESSFUL in 6s

$ java -jar build/libs/emailer.jar 
Error: Could not find or load main class us.company.emailer.App

但是当我unzip jar时，我可以看到App.class

But when I unzip the jar, I can see App.class

user@computer:../libs$ unzip emailer.jar 
Archive:  emailer.jar
   creating: META-INF/
  inflating: META-INF/MANIFEST.MF    
   creating: us/
   creating: us/company/
   creating: us/company/emailer/
  inflating: us/company/emailer/App.class

这是build.gradle

plugins {
    id 'groovy'
    id 'application'
}

repositories {
    jcenter()
    mavenCentral()
}

dependencies {
    implementation 'org.codehaus.groovy:groovy-all:2.5.6'
    testImplementation 'org.spockframework:spock-core:1.2-groovy-2.5'
    compile 'org.apache.commons:commons-email:1.5'
}

mainClassName = 'us.company.emailer.App'

jar {
    manifest {
        attributes(
            'Class-Path': configurations.compile.collect { it.getName() }.join(' '),
            'Main-Class': 'us.company.emailer.App'
        )
    }
}

sourceSets.main.java.srcDirs = ['src/main/groovy']

这是App.groovy

package us.company.emailer

class App {

    String getGreeting() {
        return 'Hello world.'
    }

    static void main(String[] args) {
        println new App().greeting
    }
}

添加MANIFEST.MF以响应@tkruse的评论

Adding MANIFEST.MF in response to the comment from @tkruse

Manifest-Version: 1.0
Class-Path: commons-email-1.5.jar javax.mail-1.5.6.jar activation-1.1.
jar
Main-Class: us.company.emailer.App

推荐答案

问题是类路径.如果您查看META-INF/MANIFEST.mf文件的内部，则可以看到它已设置为:

The problem is the classpath. If you look inside the META-INF/MANIFEST.mf file, you can see it's set to:

Class-Path: commons-email-1.5.jar javax.mail-1.5.6.jar activation-1.1.
 jar

当Java运行时，它不知道这些东西在哪里，它还需要groovy运行时才能理解您的groovy代码.

When java runs, it has no idea where any of these things are, it also requires the groovy runtime in order to understand your groovy code.

执行此操作的最简单方法是将所有依赖项捆绑到" fat-jar "中，而使用Gradle执行此操作的最简单方法是出色的

The simplest way of doing this is to bundle all your dependencies into a "fat-jar", and the simplest way of doing this with Gradle is the excellent Shadow-jar plugin.

如果将以下内容添加到build.gradle中的plugins块中:

If you add the following to your plugins block in build.gradle:

    id 'com.github.johnrengelman.shadow' version '5.0.0'

(您可以删除jar块和操纵sourceSets的行)

(You can delete the jar block and the line that manipulates the sourceSets)

然后运行./gradlew shadowJar

您将获得一个jar文件emailer-all.jar

You'll get a jar file emailer-all.jar

可以运行哪个:

$ java -jar build/libs/emailer-all.jar
Hello world.

为完整起见，这是完整的build.gradle文件:

For completeness, here's the complete build.gradle file:

plugins {
    id 'groovy'
    id 'application'
    id 'com.github.johnrengelman.shadow' version '5.0.0'
}

repositories {
    jcenter()
    mavenCentral()
}

dependencies {
    implementation 'org.codehaus.groovy:groovy-all:2.5.6'
    testImplementation 'org.spockframework:spock-core:1.2-groovy-2.5'
    implementation 'org.apache.commons:commons-email:1.5'
}

mainClassName = 'us.company.emailer.App'

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