Java进阶之SPI机制详解

static {
        loadInitialDrivers();
        println("JDBC DriverManager initialized");
}

private static void loadInitialDrivers() {
        .....
        AccessController.doPrivileged(new PrivilegedAction<Void>() {
            public Void run() {
				//使用ServiceLoader动态加载具体的驱动实现类
                ServiceLoader<Driver> loadedDrivers = ServiceLoader.load(Driver.class);
                Iterator<Driver> driversIterator = loadedDrivers.iterator();
                try{
                    while(driversIterator.hasNext()) {
                        driversIterator.next();
                    }
                } catch(Throwable t) {
                // Do nothing
                }
                return null;
            }
        });
		.....
    }

package cn.bigcoder.spi.operate.service;

/**
 * @author: Jindong.Tian
 * @date: 2020-11-29
 * @description:
 **/
public interface INumOperate {

    int exec(int num1, int num2);
}

package cn.bigcoder.spi.operate.add;


import cn.bigcoder.spi.operate.service.INumOperate;

/**
 * @author: Jindong.Tian
 * @date: 2020-11-29
 * @description:
 **/
public class NumAddOperateImpl implements INumOperate {

    public int exec(int num1, int num2) {
        return num1 + num2;
    }
}

cn.bigcoder.spi.operate.add.NumAddOperateImpl

package cn.bigcoder.spi.operate.multiplication;

import cn.bigcoder.spi.operate.service.INumOperate;

/**
 * @author: Jindong.Tian
 * @date: 2020-11-29
 * @description:
 **/
public class NumMultiOperateImpl implements INumOperate {
    
    public int exec(int num1, int num2) {
        return num1 * num2;
    }
}

cn.bigcoder.spi.operate.multiplication.NumMultiOperateImpl

package cn.bigcoder.spi.operate;

import cn.bigcoder.spi.operate.service.INumOperate;
import org.junit.Test;

import java.util.Iterator;
import java.util.ServiceLoader;

/**
 * @author: Jindong.Tian
 * @date: 2020-11-29
 * @description:
 **/
public class INumOperateTest {
    @Test
    public void test() {
        // SPI机制，寻找所有的实现类，顺序执行
        ServiceLoader<INumOperate> loader = ServiceLoader.load(INumOperate.class);
        Iterator<INumOperate> iterator = loader.iterator();
        if (iterator.hasNext()) {
            INumOperate numOperate = iterator.next();
            System.out.println(numOperate.exec(1, 2));
        } else {
            throw new RuntimeException("classpath中未找到cn.bigcoder.spi.operate.INumOperate实现类");
        }
    }
}