如何打一个FatJar（uber-jar）

FatJar也就叫做UberJar，是一种可执行的Jar包(Executable Jar)。FatJar和普通的jar不同在于它包含了依赖的jar包。

1. maven-jar-plugin

例子

<build>

    <finalName>demo</finalName>

    <plugins>

        <plugin>

            <groupId>org.apache.maven.plugins</groupId>

            <artifactId>maven-dependency-plugin</artifactId>

            <version>3.0.0</version>

            <executions>

                <execution>

                    <id>copy-dependencies</id>

                    <phase>prepare-package</phase>

                    <goals>

                        <goal>copy-dependencies</goal>

                    </goals>

                    <configuration>

                        <outputDirectory>${project.build.directory}/lib</outputDirectory>

                        <overWriteReleases>false</overWriteReleases>

                        <overWriteSnapshots>false</overWriteSnapshots>

                        <overWriteIfNewer>true</overWriteIfNewer>

                    </configuration>

                </execution>

            </executions>

        </plugin>

        <plugin>

            <groupId>org.apache.maven.plugins</groupId>

            <artifactId>maven-jar-plugin</artifactId>

            <version>3.0.2</version>

            <configuration>

                <archive>

                    <manifest>

                        <addClasspath>true</addClasspath>

                        <classpathPrefix>lib/</classpathPrefix>

                        <mainClass>com.yourcompay.Demo</mainClass>

                    </manifest>

                </archive>

            </configuration>

        </plugin>

    </plugins>

</build>

首先使用maven-dependency-plugin把依赖全部copy到outputDirectory中，为了将包打到一个jar中，需要把outputDirectory配置到classes/lib中
使用maven-jar-plugin指定MainClass和classpath，需要注意的是classpathPrefix必须是${project.build.finalName}/lib路径
执行命令

java -jar ./target/demo.jar

注意：采用maven-jar-plugin方式有个缺点，demo.jar不能移动到其他路径下面执行java -jar命令，因为demo.jar依赖放在了lib/目录下

解决方法有点复杂，首先用maven-dependency-plugin把依赖copy到${project.build.directory}/classes/lib，然后需要自定义jar加载的classloader，真复杂...

2. maven-assembly-plugin

maven-assembly-plugin是一个强大的打包工具，除了jar包还能打zip、tar.gz、tar.bz2等类型的包，描述文件放在assembly.xml中

如何用assembly打一个FatJar，使用预定义格式jar-with-dependencies打包

实际上

<build>

    <finalName>demo</finalName>

    <plugins>

        <plugin>

            <groupId>org.apache.maven.plugins</groupId>

            <artifactId>maven-assembly-plugin</artifactId>

            <version>3.0.0</version>

            <configuration>

                <archive>

                    <manifest>

                        <mainClass>com.yourcompany.Demo</mainClass>

                    </manifest>

                </archive>

                <descriptorRefs>

                    <descriptorRef>jar-with-dependencies</descriptorRef>

                </descriptorRefs>

            </configuration>

            <executions>

                <execution>

                    <id>make-assembly</id>

                    <phase>package</phase>

                    <goals>

                        <goal>single</goal>

                    </goals>

                </execution>

            </executions>

        </plugin>

    </plugins>

</build>

执行命令make clean package，得到demo-jar-with-dependencies.jar，这时我们就可以使用java -jar命令了

注意：预定义格式jar-with-dependencies实际上只有基本的FatJar打包功能，背后集成是maven-shade-plugin。下一节就讲shade-plugin

3. maven-shade-plugin

3.1 一个简单的例子

maven-shade-plugin将goal shade:shade绑定到maven的package阶段

<build>

    <finalName>demo</finalName>

    <plugins>

        <plugin>

            <artifactId>maven-shade-plugin</artifactId>

            <version>3.0.0</version>

            <executions>

                <execution>

                    <phase>package</phase>

                    <goals>

                        <goal>shade</goal>

                    </goals>

                </execution>

            </executions>

        </plugin>

    </plugins>

</build>

执行命令maven package在target目录下生成一个demo.jar

3.2 设置MainClass创建一个可执行的Jar包

<build>

    <finalName>demo</finalName>

    <plugins>

        <plugin>

            <artifactId>maven-shade-plugin</artifactId>

            <version>3.0.0</version>

            <executions>

                <execution>

                    <phase>package</phase>

                    <goals>

                        <goal>shade</goal>

                    </goals>

                    <configuration>

                        <transformers>

                            <transformer implementation="org.apache.maven.plugins.shade.resource.ManifestResourceTransformer">

                                <manifestEntries>

                                    <Main-Class>com.yourcompany.Demo</Main-Class>

                                </manifestEntries>

                            </transformer>

                        </transformers>

                    </configuration>

                </execution>

            </executions>

        </plugin>

    </plugins>

</build>

执行mvn package命令生成一个demo.jar，执行demo.jar

java -jar ./target/demo.jar

3.2.1 Resource Transformers

AppendingTransformer 增加一个文件到resource
XmlAppendingTransformer 增加一个xml到resource
ManifestResourceTransformer 设置MANIFEST

3.3 使用include/exclude指定需要打包的jar

在configuration元素下增加includes和excludes节点

<configuration>

  <artifactSet>

    <includes>

      <include>org.apache.commons:commons-langs</include>

    </includes>

    <excludes>

      <exclude>com.alibaba:fastjson</exclude>

    </excludes>

  </artifactSet>

</configuration>

3.4 使用filter过滤jar包中的类或者资源

在configuration元素下增加filters节点

<configuration>

  <filters>

    <filter>

      <artifact>junit:junit</artifact>

      <includes>

        <include>junit/framework/**</include>

        <include>org/junit/**</include>

      </includes>

      <excludes>

        <exclude>org/junit/experimental/**</exclude>

        <exclude>org/junit/runners/**</exclude>

      </excludes>

    </filter>

  </filters>

</configuration>

3.5 maven-shade-plugin 自动将所有不使用的类全部排除掉

<executions>

  <execution>

    <phase>package</phase>

    <goals>

      <goal>shade</goal>

    </goals>

    <configuration>

      <minimizeJar>true</minimizeJar>

    </configuration>

  </execution>

</executions>