本文主要研究下如何在maven里头构建java9 multi module及service实例
整个工程跟传统maven多module的工程结构一样,java9的一个module对应maven project的一个module。下面是根目录下的pom文件:
<?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.example</groupId>
<artifactId>java9-service-demo</artifactId>
<version>0.0.1-SNAPSHOT</version>
<modules>
<module>consumer-demo</module>
<module>service-sort</module>
<module>service-sort-bubble</module>
<module>service-sort-merge</module>
</modules>
<packaging>pom</packaging>
<properties>
<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
<!--让intellij能够正确编译java9,不然老是变回使用1.5-->
<maven.compiler.source>9</maven.compiler.source>
<maven.compiler.target>9</maven.compiler.target>
</properties>
<build>
<pluginManagement>
<plugins>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-compiler-plugin</artifactId>
<version>3.6.1</version>
<configuration>
<release>9</release>
</configuration>
</plugin>
</plugins>
</pluginManagement>
</build>
</project>
这里管理了一个maven-compiler-plugin,配置release为9,因为java9支持multi release,可以同时支持多个java版本,这里编译为java9版本。
这个是service接口module
module service.sort {
exports service.sort;
uses service.sort.SortService;
}
这里同时声明uses SortService表示是它需要在这个module里头使用ServiceLoader去加载service实例
public interface SortService {
public <T extends Comparable> List<T> sortList(List<T> list);
public static SortService getProviderInstanceLazy() {
Stream<Provider<SortService>> providers = ServiceLoader.load(SortService.class)
.stream();
//provider方法等到get的时候才会实例化
SortService service = providers.map(Provider::get)
.findAny()
.orElse(null);
return service;
}
}
这里在声明接口的同时,也增加了静态方法,用于加载service实例。
<?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">
<parent>
<artifactId>java9-service-demo</artifactId>
<groupId>com.example</groupId>
<version>0.0.1-SNAPSHOT</version>
</parent>
<modelVersion>4.0.0</modelVersion>
<groupId>com.example</groupId>
<artifactId>service-sort-bubble</artifactId>
<packaging>jar</packaging>
<dependencies>
<dependency>
<groupId>com.example</groupId>
<artifactId>service-sort</artifactId>
<version>0.0.1-SNAPSHOT</version>
</dependency>
</dependencies>
</project>
这里添加对api包的依赖
import java.util.List;
import java.util.ArrayList;
import java.util.Collections;
import java.util.Arrays;
import service.sort.SortService;
public class MergeSort implements SortService {
public <T extends Comparable> List<T> sortList(List<T> list) {
System.out.println("using MergeSort");
Collections.sort(list);
return list;
}
}
<?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">
<parent>
<artifactId>java9-service-demo</artifactId>
<groupId>com.example</groupId>
<version>0.0.1-SNAPSHOT</version>
</parent>
<modelVersion>4.0.0</modelVersion>
<groupId>com.example</groupId>
<artifactId>consumer-demo</artifactId>
<packaging>jar</packaging>
<dependencies>
<dependency>
<groupId>com.example</groupId>
<artifactId>service-sort</artifactId>
<version>0.0.1-SNAPSHOT</version>
</dependency>
</dependencies>
</project>
注意这里没有添加实现类的依赖
输出
sort service consumer started.
use BubbleSort
[2, 3, 5, 8, 10]
finish
输出
sort service consumer started.
using MergeSort
[2, 3, 5, 8, 10]
finish
或者
java --module-path ./consumer-demo/target/consumer-demo-0.0.1-SNAPSHOT.jar:./service-sort/target/service-sort-0.0.1-SNAPSHOT.jar:./service-sort-merge/target/service-sort-merge-0.0.1-SNAPSHOT.jar:./service-sort-bubble/target/service-sort-bubble-0.0.1-SNAPSHOT.jar --module consumer/consumer.Main
输出
sort service consumer started.
use BubbleSort
[2, 3, 5, 8, 10]
finish
发现貌似跟添加到path的顺序没有关系,即使把merge的jar包放在前面,也是使用bubble
在java6的时候就已经有ServiceLoader了,不过那个时候是依赖在jar包的META-INF/services目录下创建一个service接口全路径名称的文件,里头写上实现类的全路径名称。java9对在引入模块化后也支持在module-info.java里头声明service的提供方和消费者信息,这样模块系统可以支持ServiceLoader,不需要使用原来的META-INF那种声明方式。