SPI简介

SPI 全称为 (Service Provider Interface) ,是JDK内置的一种服务提供发现机制。为某一接口实现服务的机制。

适用场景

项目版本升级，不同开发人员负责自己的模块的升级且互不干扰。（公司项目中场景）

案例说明

• 接口定义

package com.upgrade;
public interface UpgradeOperation {
    /**
     * 执行更新方法
     */
    void execute(OperationContext context);

    /**
     * 版本信息
     */
    OSVersionBuild build();

    /**
     * 执行同一版本更新优先级（从小到大依次执行）
     * @return
     */
    int priority();

    /**
     * 唯一标识符
     * @return
     */
    String getId();
}

• 接口实现
  UdsqlUpgradeOperation7_3_1Impl

package com.upgrade.impl;
public class UdsqlUpgradeOperation7_3_1Impl implements UpgradeOperation {

    @Override
    public void execute(OperationContext context) {

    }

    @Override
    public OSVersionBuild build() {
        return OSVersionBuild.VERSION_7_3_1;
    }

    @Override
    public int priority() {
        return 0;
    }

    @Override
    public String getId() {
        return "7.3.1_udsql";
    }
}

UdsqlUpgradeOperation7_3_2Impl

package com.upgrade.impl;
public class UdsqlUpgradeOperation7_3_2Impl implements UpgradeOperation {

    @Override
    public void execute(OperationContext context) {

    }

    @Override
    public OSVersionBuild build() {
        return OSVersionBuild.VERSION_7_3_1;
    }

    @Override
    public int priority() {
        return 0;
    }

    @Override
    public String getId() {
        return "7.3.2_udsql";
    }
}

• 实现SPI需要在META-INF/services中新建以服务接口命名的文件com.upgrade.UpgradeOperation.内容如下：

com.upgrade.impl.UdsqlUpgradeOperation7_3_1Impl
com.upgrade.impl.UdsqlUpgradeOperation7_3_2Impl

• 客户端代码

    public static List<UpgradeOperation> getUpgradeOperations() {
        List<UpgradeOperation> upgradeOperations = new ArrayList<>();
        ServiceLoader<UpgradeOperation> operations = ServiceLoader.load(UpgradeOperation.class);
        Iterator<UpgradeOperation> iterator = operations.iterator();
        while (iterator.hasNext()) {
            UpgradeOperation operation = iterator.next();
            upgradeOperations.add(operation);
        }
        return upgradeOperations;
    }

利用SPI机制可以获取目录下所有UpgradeOperation接口的实现。