我们把之前在一个项目中实现SPI机制的简单例子(参见Java的SPI简单实例 ),换成实际使用中的jar包引入的简单例子。一拆为三,接口一个包,实现一个包,应用一个包,哦,还得加个骨架包。我们新增一个父项目:在IDEA中点击左上角File -> 点New Project -> 点Maven -> 点Next -> 输入Maven的groupId和artifactId后点Next -> 输入项目名后点Finish,只需在pom文件中新增module:
<?xml version="1.0" encoding="UTF-8"?> <project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd"> <modelVersion>4.0.0</modelVersion> <groupId>com.wlf.spi</groupId> <artifactId>spi-parent</artifactId> <version>1.0-SNAPSHOT</version> <packaging>pom</packaging> <properties> <java.version>1.8</java.version> </properties> <modules> <module>spi-api</module> <module>spi-impl</module> <module>spi-app</module> </modules> <build> <plugins> <plugin> <groupId>org.apache.maven.plugins</groupId> <artifactId>maven-compiler-plugin</artifactId> <configuration> <source>1.8</source> <target>1.8</target> </configuration> </plugin> </plugins> </build> </project>
然后继续依葫芦画瓢,分别新增如上三个子项目:接口spi-api,实现spi-impl和应用spi-app。为了使用接口,spi-impl和spi-app都依赖了spi-api包,spi-app加载实现类,还得引入spi-impl包。看看子项目的pom.xml:
<?xml version="1.0" encoding="UTF-8"?> <project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd"> <modelVersion>4.0.0</modelVersion> <parent> <groupId>com.wlf.spi</groupId> <artifactId>spi-parent</artifactId> <version>1.0-SNAPSHOT</version> </parent> <artifactId>spi-api</artifactId> <version>1.0-SNAPSHOT</version> <packaging>jar</packaging> </project>
<?xml version="1.0" encoding="UTF-8"?> <project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd"> <modelVersion>4.0.0</modelVersion> <parent> <groupId>com.wlf.spi</groupId> <artifactId>spi-parent</artifactId> <version>1.0-SNAPSHOT</version> </parent> <artifactId>spi-app</artifactId> <version>1.0-SNAPSHOT</version> <packaging>jar</packaging> <dependencies> <dependency> <groupId>com.wlf.spi</groupId> <artifactId>spi-api</artifactId> <version>1.0-SNAPSHOT</version> </dependency> <dependency> <groupId>com.wlf.spi</groupId> <artifactId>spi-impl</artifactId> <version>1.0-SNAPSHOT</version> </dependency> </dependencies> </project>
<?xml version="1.0" encoding="UTF-8"?> <project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd"> <modelVersion>4.0.0</modelVersion> <parent> <groupId>com.wlf.spi</groupId> <artifactId>spi-parent</artifactId> <version>1.0-SNAPSHOT</version> </parent> <artifactId>spi-impl</artifactId> <version>1.0-SNAPSHOT</version> <packaging>jar</packaging> <dependencies> <dependency> <groupId>com.wlf.spi</groupId> <artifactId>spi-api</artifactId> <version>1.0-SNAPSHOT</version> </dependency> </dependencies> <build> <resources> <resource> <directory>src/main/resources</directory> <targetPath>META-INF/</targetPath> </resource> </resources> </build> </project>
上面resource节点是为了把spi-impl包中的resources目录下的内容在打jar包时,复制到META-INF目录中,输出META-INF/services/com.wlf.api.ITest这个文件。这个文件的内容执行实现类:
其他的接口类、实现类和应用类代码不变,包路径改改就好:
跑一把,结果跟之前在单一项目跑的结果是一样的: