使用maven構建java9 service實例詳解

序

本文主要研究下如何在maven裡頭構建java9 multi module及service實例

maven

整個工程跟傳統maven多module的工程結構一樣，java9的一個module對應maven project的一個module。下面是根目錄下的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> <!--讓intellij能夠正確編譯java9，不然老是變回使用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>

這裡管理了一個maven-compiler-plugin，配置release為9，因為java9支持multi release，可以同時支持多個java版本，這裡編譯為java9版本。

service-sort

這個是service接口module

 module service.sort { exports service.sort; uses service.sort.SortService;}

這裡同時聲明uses SortService表示是它需要在這個module裡頭使用ServiceLoader去加載service實例

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的時候才會實例化SortService service = providers.map(Provider::get) .findAny() .orElse(null); return service; }}

這裡在聲明接口的同時，也增加了靜態方法，用於加載service實例。

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>

這裡添加對api包的依賴

module-info.java

 module service.sort.bubble { requires service.sort; provides service.sort.SortService with sort.impl.bubble.BubbleSort;}

這裡聲明了BubbleSort提供了SortService的實現

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;}

這裡聲明了MergeSort為SortService接口的實現

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>

注意這裡沒有添加實現類的依賴

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"); }}

編譯及運行

編譯

mvn clean install

這裡是在根目錄下執行

使用bubble

複製代碼代碼如下:
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

注意這裡添加了bubble的jar到module-path

輸出

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

使用merge

複製代碼代碼如下:
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

注意這裡添加了merge的jar到module-path

輸出

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

兩個service實現都添加

複製代碼代碼如下:
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

複製代碼代碼如下:
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

輸出

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

發現貌似跟添加到path的順序沒有關係，即使把merge的jar包放在前面，也是使用bubble

小結

在java6的時候就已經有ServiceLoader了，不過那個時候是依賴在jar包的META-INF/services目錄下創建一個service接口全路徑名稱的文件，裡頭寫上實現類的全路徑名稱。 java9對在引入模塊化後也支持在module-info.java裡頭聲明service的提供方和消費者信息，這樣模塊系統可以支持ServiceLoader，不需要使用原來的META-INF那種聲明方式。

以上就是本文的全部內容，希望對大家的學習有所幫助，也希望大家多多支持武林網。