title: 合并依赖包内 META-INF
categories:

打包成单体 jar 包

在很多场景下，需要将程序及依赖打包为单个 jar 包，方便部署、运行。打包成单体 jar 包，有多个插件可选，比如 maven-shade-plugin、maven-assembly-plugin。

合并 META-INF/services

以 gRPC 为例，我们有一个依赖包，里面自定义了 NameResolver。

# META-INF/services/io.grpc.NameResolverProvider
pub.wii.cook.governance.nameresolver.DynamicNameResolverProvider

如果我们恰巧引用了另外一个依赖包（jetcd-core），里面定义了其他的 NameResolver。

# META-INF/services/io.grpc.NameResolverProvider
io.etcd.jetcd.resolver.DnsSrvResolverProvider
io.etcd.jetcd.resolver.IPResolverProvider

那么，在我们打包成单体 jar 时，将两个依赖包内的 META-INF/services/io.grpc.NameResolverProvider 合并为一个，这样打包后的程序在运行时才可以通过 SPI 机制，找到所有的扩展。

# 期望的打包后 META-INF/services/io.grpc.NameResolverProvider
io.etcd.jetcd.resolver.DnsSrvResolverProvider
io.etcd.jetcd.resolver.IPResolverProvider
pub.wii.cook.governance.nameresolver.DynamicNameResolverProvider

无论 maven-shade-plugin 还是 maven-assembly-plugin，默认配置都不支持合并，需要单独配置。

对于 maven-shade-plugin ，需要添加 transformer。

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

对于 maven-assembly-plugin ，需要添加组装描述文件 assembly.xml，并启用 handler metaInf-services。

<!-- assembly.xml -->
<assembly xmlns="http://maven.apache.org/ASSEMBLY/2.1.0"
          xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
          xsi:schemaLocation="http://maven.apache.org/ASSEMBLY/2.1.0
            http://maven.apache.org/xsd/assembly-2.1.0.xsd">
    <id>jar-with-dependencies</id>
    <formats>
        <format>jar</format>
    </formats>

    <includeBaseDirectory>false</includeBaseDirectory>
    <dependencySets>
        <dependencySet>
            <outputDirectory>/</outputDirectory>
            <useProjectArtifact>true</useProjectArtifact>
            <unpack>true</unpack>
            <scope>runtime</scope>
        </dependencySet>
    </dependencySets>

    <containerDescriptorHandlers>
        <containerDescriptorHandler>
            <handlerName>metaInf-services</handlerName>
        </containerDescriptorHandler>
    </containerDescriptorHandlers>
</assembly>

配置示例

maven-shade-plugin 和 maven-assembly-plugin 配置，二选一。

maven-shade-plugin

<plugin>
    <groupId>org.apache.maven.plugins</groupId>
    <artifactId>maven-shade-plugin</artifactId>
    <version>3.2.4</version>
    <configuration>
        <filters>
            <filter>
                <artifact>*:*</artifact>
                <excludes>
                    <exclude>META-INF/*.SF</exclude>
                    <exclude>META-INF/*.DSA</exclude>
                    <exclude>META-INF/*.RSA</exclude>
                </excludes>
            </filter>
        </filters>
    </configuration>
    <executions>
        <execution>
            <phase>package</phase>
            <goals>
                <goal>shade</goal>
            </goals>
            <configuration>
                <transformers>
                    <transformer implementation="org.apache.maven.plugins.shade.resource.ServicesResourceTransformer"/>
                    <transformer implementation="org.apache.maven.plugins.shade.resource.ManifestResourceTransformer">
                        <mainClass>pub.wii.cook.Main</mainClass>
                    </transformer>
                </transformers>
            </configuration>
        </execution>
    </executions>
</plugin>

maven-assembly-plugin

<plugin>
    <groupId>org.apache.maven.plugins</groupId>
    <artifactId>maven-assembly-plugin</artifactId>
    <version>3.3.0</version>
    <executions>
        <execution>
            <phase>package</phase>
            <goals>
                <goal>single</goal>
            </goals>
            <configuration>
                <descriptors>
                    <descriptor>src/assemble/assembly.xml</descriptor>
                </descriptors>
                <archive>
                    <manifest>
                        <mainClass>pub.wii.cook.Main</mainClass>
                    </manifest>
                </archive>
            </configuration>
        </execution>
    </executions>
</plugin>

assembly.xml

<assembly xmlns="http://maven.apache.org/ASSEMBLY/2.1.0"
          xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
          xsi:schemaLocation="http://maven.apache.org/ASSEMBLY/2.1.0
            http://maven.apache.org/xsd/assembly-2.1.0.xsd">
    <id>jar-with-dependencies</id>
    <formats>
        <format>jar</format>
    </formats>

    <includeBaseDirectory>false</includeBaseDirectory>
    <dependencySets>
        <dependencySet>
            <outputDirectory>/</outputDirectory>
            <useProjectArtifact>true</useProjectArtifact>
            <unpack>true</unpack>
            <scope>runtime</scope>
        </dependencySet>
    </dependencySets>

    <containerDescriptorHandlers>
        <containerDescriptorHandler>
            <handlerName>metaInf-services</handlerName>
        </containerDescriptorHandler>
    </containerDescriptorHandlers>
</assembly>

参考