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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
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:
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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 > |
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 { 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
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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; } } |
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
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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 > |
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; } |
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); } } |
service-sort-merge
maven
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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 > |
module-info.java
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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
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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; } } |
consumer
maven
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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 > |
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; } |
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" ); } } |
编译及运行
编译
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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。
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服务器之家。
原文链接:https://juejin.im/post/5a9269c85188257a84625450