使用maven构建java9 service实例

code4it

发布于 2018-09-17 15:54:28

5640

发布于 2018-09-17 15:54:28

文章被收录于专栏：码匠的流水账

序

本文主要研究下如何在maven里头构建java9 multi module及service实例

maven

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。

service-sort

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。

service-sort-bubble

maven

<?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

module-info.java module service.sort.bubble { requires service.sort; provides service.sort.SortService with sort.impl.bubble.BubbleSort; } 这里声明了BubbleSort提供了SortService的实现
BubbleSort public class BubbleSort implements SortService { public <T extends Comparable> List<T> sortList(List<T> list) { System.out.println("use BubbleSort"); for (int outer = 0; outer < list.size() - 1; outer++) { for (int inner = 0; inner < list.size()-outer-1; inner++) { if (list.get(inner).compareTo(list.get(inner + 1)) > 0) { swap(list, inner); } } } return list; } private <T> void swap(List<T>list, int inner) { T temp = list.get(inner); list.set(inner, list.get(inner + 1)); list.set(inner + 1, temp); } }

service-sort-merge

maven <?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-merge</artifactId> <packaging>jar</packaging> <dependencies> <dependency> <groupId>com.example</groupId> <artifactId>service-sort</artifactId> <version>0.0.1-SNAPSHOT</version> </dependency> </dependencies> </project>
module-info.java module service.sort.merge { requires service.sort; provides service.sort.SortService with sort.impl.merge.MergeSort; } 这里声明了MergeSort为SortService接口的实现
MergeSort

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;
    }
}

consumer

maven

<?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

module-info.java module consumer { requires service.sort; }
Main public class Main { public static void main(String[] args) { System.out.println("sort service consumer started."); List<Integer> data = new ArrayList<Integer>(); data.add(5); data.add(3); data.add(10); data.add(2); data.add(8); SortService sortService = SortService.getProviderInstanceLazy(); if (sortService != null) { sortService.sortList(data); } System.out.println(data); System.out.println("finish"); } }

编译及运行

编译 mvn clean install 这里是在根目录下执行
使用bubble 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-bubble/target/service-sort-bubble-0.0.1-SNAPSHOT.jar --module consumer/consumer.Main 注意这里添加了bubble的jar到module-path

输出

sort service consumer started.
use BubbleSort
[2, 3, 5, 8, 10]
finish

使用merge 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 --module consumer/consumer.Main 注意这里添加了merge的jar到module-path

输出

sort service consumer started.
using MergeSort
[2, 3, 5, 8, 10]
finish

两个service实现都添加 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-bubble/target/service-sort-bubble-0.0.1-SNAPSHOT.jar:./service-sort-merge/target/service-sort-merge-0.0.1-SNAPSHOT.jar --module consumer/consumer.Main

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

小结

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。