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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：
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<?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>
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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
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module service.sort {
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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
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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;
}
}
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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
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<?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>
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这里添加对api包的依赖
module-info.java
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module service.sort.bubble {
requires service.sort;
provides service.sort.SortService with sort.impl.bubble.BubbleSort;
}
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这里声明了BubbleSort提供了SortService的实现
BubbleSort
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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);
}
}
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service-sort-merge
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<?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>
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module-info.java
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module service.sort.merge {
requires service.sort;
provides service.sort.SortService with sort.impl.merge.MergeSort;
}
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这里声明了MergeSort为SortService接口的实现
MergeSort
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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;
}
}
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consumer
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<?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>
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注意这里没有添加实现类的依赖
module-info.java
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module consumer {
requires service.sort;
}
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Main
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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");
}
}
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编译及运行
编译
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mvn clean install
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这里是在根目录下执行
使用bubble
复制代码 代码如下:
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
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
复制代码 代码如下:
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
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
复制代码 代码如下:
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
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
复制代码 代码如下:
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
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。
以上就是本文的全部内容，希望对大家的学习有所帮助，也希望大家多多支持快网idc。
原文链接：https://juejin.im/post/5a9269c85188257a84625450
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