详解如何使用maven生成可以执行的jar

不依赖任何外界包，maven如何生成可以执行的jar?

pom中不包含任何引用的情况下，只需要在pom中添加 maven-jar-plugin即可。

解决过程

新建项目，仅包含一个main函数类：Xixi.java，输出 Xixi Say: hello

pom中配置为

<groupId>com.paxi</groupId>
 <artifactId>xixi</artifactId>
 <version>1.0-SNAPSHOT</version>
 <packaging>jar</packaging>

 <name>xixi</name>
 <url>http://maven.apache.org</url>

 <properties>
  <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
 </properties>

执行 mvn clean install 生成jar包 xixi-1.0-SNAPSHOT.jar,执行jar命令,执行反馈出错

 java -jar xixi-1.0-SNAPSHOT.jar
xixi-1.0-SNAPSHOT.jar中没有主清单属性

对jar进行解压缩jar xvf xixi-1.0-SNAPSHOT.jar查看对应文件MANIFEST.MF

 cat META-INF/MANIFEST.MF
Manifest-Version: 1.0
Archiver-Version: Plexus Archiver
Built-By: paxi
Created-By: Apache Maven 3.3.3
Build-Jdk: 1.8.0_121

在pom中添加插件 maven-jar-plugin

<build>
  <plugins>
   <plugin>
    <groupId>org.apache.maven.plugins</groupId>
    <artifactId>maven-jar-plugin</artifactId>
    <version>3.1.0</version>
    <configuration>
     <archive>
      <manifest>
       <mainClass>com.paxi.Xixi</mainClass>
      </manifest>
     </archive>
    </configuration>
   </plugin>
  </plugins>
 </build>

执行成功输出

java -jar xixi-1.0-SNAPSHOT.jar
Xixi Say: hello

再对解压缩后的MANIFEST.MF文件查看为

 cat META-INF/MANIFEST.MF
Manifest-Version: 1.0
Built-By: paxi
Created-By: Apache Maven 3.3.3
Build-Jdk: 1.8.0_121
Main-Class: com.paxi.Xixi //新增

在pom中添加依赖，maven如何生成可执行jar?

需要使用插件maven-dependency-plugin 和 maven-jar-plugin。

解决过程

在pom中仅仅增加一个apache-commons包

<groupId>com.paxi</groupId>
 <artifactId>xixi</artifactId>
 <version>1.0-SNAPSHOT</version>
 <packaging>jar</packaging>

 <name>xixi</name>
 <url>http://maven.apache.org</url>

 <properties>
  <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
 </properties>
 <dependencies>

   <dependency>
    <groupId>org.apache.commons</groupId>
    <artifactId>commons-lang3</artifactId>
    <version>3.7</version>
  </dependency>

 </dependencies>

在代码中运用common包中的一个类

 public static void main(String[] args) {
    String words = "Xixi Say: hello";
    if (StringUtils.isNotBlank(words))
    {
      System.out.println(words);
    }
  }

打包后直接运行出错

java -jar xixi-1.0-SNAPSHOT.jar
Exception in thread "main" java.lang.NoClassDefFoundError: org/apache/commons/lang3/StringUtils
    at com.paxi.Xixi.main(Xixi.java:11)
Caused by: java.lang.ClassNotFoundException: org.apache.commons.lang3.StringUtils
    at java.net.URLClassLoader.findClass(URLClassLoader.java:381)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:424)
    at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:331)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:357)
    ... 1 more

在pom中增加插件

<build>
  <plugins>
   <plugin>
    <groupId>org.apache.maven.plugins</groupId>
    <artifactId>maven-jar-plugin</artifactId>
    <version>3.1.0</version>
    <configuration>
     <archive>
      <manifest>
       <addClasspath>true</addClasspath>
       <mainClass>com.paxi.Xixi</mainClass>
       <classpathPrefix>libs/</classpathPrefix>
      </manifest>
     </archive>
    </configuration>
   </plugin>

   <plugin>
    <groupId>org.apache.maven.plugins</groupId>
    <artifactId>maven-dependency-plugin</artifactId>
    <version>3.1.1</version>
    <executions>
     <execution>
      <id>copy-dependencies</id>
      <phase>package</phase>
      <goals>
       <goal>copy-dependencies</goal>
      </goals>
      <configuration>
       <outputDirectory>
        ${project.build.directory}/libs
       </outputDirectory>
      </configuration>
     </execution>
    </executions>
   </plugin>

  </plugins>
 </build>

再次运行

 java -jar xixi-1.0-SNAPSHOT.jar
Xixi Say: hello

MANIFEST.MF文件为

 cat META-INF/MANIFEST.MF
Manifest-Version: 1.0
Built-By: paxi
Class-Path: libs/commons-lang3-3.7.jar
Created-By: Apache Maven 3.3.3
Build-Jdk: 1.8.0_121
Main-Class: com.paxi.Xixi

不仅使用了POM中的依赖还使用了三方的jar,maven如何生成可执行jar?

编译过程需要对编译插件 maven-compiler-plugin做修改，运行的时候需要加上三方jar的目录，执行命令

 java -jar -Djava.ext.dirs=lib/ target/xixi-1.0-SNAPSHOT.jar
Xixi Say: hello
Papa say:hello

编译解决过程

测试代码为

 public static void main(String[] args) {
    String words = "Xixi Say: hello";
    if (StringUtils.isNotBlank(words))
    {
      System.out.println(words);
    }
    Papa.say();
  }

使用mvn命令执行报错

[ERROR] Failed to execute goal org.apache.maven.plugins:maven-compiler-plugin:3.1:compile (default-compile) on project xixi: Compilation failure
xixi/src/main/java/com/paxi/Xixi.java:[15,9] 找不到符号

pom中添加编译插件

<plugin>
    <groupId>org.apache.maven.plugins</groupId>
    <artifactId>maven-compiler-plugin</artifactId>
    <version>3.1</version>
    <configuration>
     <compilerArgs>
      <arg>-Djava.ext.dirs=lib/</arg>
     </compilerArgs>
    </configuration>
   </plugin>

打包执行

 java -jar target/xixi-1.0-SNAPSHOT.jar
Xixi Say: hello
Exception in thread "main" java.lang.NoClassDefFoundError: com/paxi/Papa
  at com.paxi.Xixi.main(Xixi.java:15)
Caused by: java.lang.ClassNotFoundException: com.paxi.Papa
  at java.net.URLClassLoader.findClass(URLClassLoader.java:381)
  at java.lang.ClassLoader.loadClass(ClassLoader.java:424)
  at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:331)
  at java.lang.ClassLoader.loadClass(ClassLoader.java:357)
  ... 1 more

加上参数后即可得出结果

 java -jar -Djava.ext.dirs=lib/ target/xixi-1.0-SNAPSHOT.jar
Xixi Say: hello
Papa say:hello

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