使用maven构建java9 service实例详解

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

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

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

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

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

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武林网。