SPI （Service Provider Interface）机制
什么是SPI机制
JDK内置的一种 服务提供发现机制，可以用来启用框架扩展和替换组件。
暴露一个公共接口，共开发人员实现，动态加载实现类。
示例
Code
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| # dubbo spi 依赖包
implementation 'org.apache.dubbo:dubbo-common:3.2.2'
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接口
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| package dekun.wang.spi.interfaces;
import org.apache.dubbo.common.extension.SPI;
@SPI
public interface Command {
void execute();
}
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| package dekun.wang.spi.interfaces.dubbo;
import org.apache.dubbo.common.extension.SPI;
@SPI
public interface CommandDubbo {
void execute();
}
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实现类
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| package dekun.wang.spi.interfaces.impl;
import dekun.wang.spi.interfaces.Command;
import org.apache.dubbo.common.extension.SPI;
import java.util.Map;
@SPI("CommandEnv")
public class CommandEnv implements Command {
@Override
public void execute() {
System.out.println("==========================");
ProcessBuilder processBuilder = new ProcessBuilder();
Map<String, String> environment = processBuilder.environment();
System.out.println("Brew=" + environment.get("Brew"));
System.out.println("--------------------------");
}
}
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| package dekun.wang.spi.interfaces.impl;
import dekun.wang.spi.interfaces.Command;
import org.apache.dubbo.common.extension.SPI;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
@SPI("CommandWhichGit")
public class CommandWhichGit implements Command {
@Override
public void execute() {
System.out.println("==========================");
try {
Process pr = Runtime.getRuntime().exec(new String[]{"/usr/bin/which", "git"});
BufferedReader br = new BufferedReader(new InputStreamReader(pr.getInputStream()));
String result;
while ((result = br.readLine()) != null) {
System.out.println(result);
}
br.close();
} catch (IOException e) {
throw new RuntimeException(e);
}
System.out.println("--------------------------");
}
}
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| package dekun.wang.spi.interfaces.impl;
import dekun.wang.spi.interfaces.Command;
import org.apache.dubbo.common.extension.SPI;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.nio.charset.StandardCharsets;
@SPI("CommandWitchLs")
public class CommandWitchLs implements Command {
@Override
public void execute() {
System.out.println("==========================");
try {
ProcessBuilder processBuilder = new ProcessBuilder();
processBuilder.command("which", "ls");
Process process = processBuilder.start();
try (BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(process.getInputStream(), StandardCharsets.UTF_8));) {
String line = null;
while ((line = bufferedReader.readLine()) != null) {
System.out.println(line);
}
}
} catch (IOException e) {
throw new RuntimeException(e);
}
System.out.println("--------------------------");
}
}
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| package dekun.wang.spi.interfaces.dubbo;
import org.apache.dubbo.common.extension.SPI;
@SPI("CommandDubboImpl")
public class CommandDubboImpl implements CommandDubbo {
@Override
public void execute() {
System.out.println("============CommandDubboImpl================");
}
}
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资源目录配置
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| $ tree -NL 4 resources
resources
├── META-INF
│ ├── dubbo
│ │ ├── dekun.wang.spi.interfaces.Command # 文件名
│ │ └── internal
│ │ └── dekun.wang.spi.interfaces.Command # 文件名
│ ├── services
│ │ ├── dekun.wang.spi.interfaces.Command # 文件名
│ │ └── dekun.wang.spi.interfaces.dubbo.CommandDubbo # 文件名
│ └── spring.factories
└── application.properties
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JDK SPI
配置
resources 配置
创建META-INF/services 目录，新建以接口全路径命名的文件，文件内没行及实现类全路径类。
META-INF/services/dekun.wang.spi.interfaces.Command
行排序及迭代顺序
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| dekun.wang.spi.interfaces.impl.CommandWhichGit
dekun.wang.spi.interfaces.impl.CommandEnv
dekun.wang.spi.interfaces.impl.CommandWitchLs
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测试类
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| package dekun.wang.spi;
import dekun.wang.spi.interfaces.Command;
import java.util.ServiceLoader;
public class TestJdkSpi {
public static void main(String[] args) {
ServiceLoader<Command> command = ServiceLoader.load(Command.class);
for (Command cmd : command) {
cmd.execute();
}
}
}
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| ==========================
/usr/local/bin/git
--------------------------
==========================
Brew=/usr/local/bin:/usr/local/sbin
--------------------------
==========================
/bin/ls
--------------------------
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Spring SPI
配置
resources 配置
目录创建 META-INF目录，并创建文件spring.factories
META-INF/spring.factories
spring.factories文件内容格式，加载顺序，及迭代顺序。
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| dekun.wang.spi.interfaces.Command=\
dekun.wang.spi.interfaces.impl.CommandWhichGit,\
dekun.wang.spi.interfaces.impl.CommandEnv,\
dekun.wang.spi.interfaces.impl.CommandWitchLs
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测试类
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| package dekun.wang.spi;
import dekun.wang.spi.interfaces.Command;
import org.springframework.core.io.support.SpringFactoriesLoader;
public class TestSpringSpi {
public static void main(String[] args) {
SpringFactoriesLoader springFactoriesLoader = SpringFactoriesLoader.forDefaultResourceLocation(Command.class.getClassLoader());
for (Command command : springFactoriesLoader.load(Command.class)) {
command.execute();
}
}
}
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| ==========================
/usr/local/bin/git
--------------------------
==========================
Brew=/usr/local/bin:/usr/local/sbin
--------------------------
==========================
/bin/ls
--------------------------
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配置
文件名：接口全路径，内容 key（注解配置key）=实现类全路径
META-INF/dubbo/internal/dekun.wang.spi.interfaces.Command
内容：CommandWhichGit=dekun.wang.spi.interfaces.impl.CommandWhichGit
META-INF/dubbo/dekun.wang.spi.interfaces.Command
内容：
CommandEnv=dekun.wang.spi.interfaces.impl.CommandEnv
CommandWitchLs=dekun.wang.spi.interfaces.impl.CommandWitchLs
META-INF/services/dekun.wang.spi.interfaces.dubbo.CommandDubbo
内容： CommandDubboImpl=dekun.wang.spi.interfaces.dubbo.CommandDubboImpl
测试类
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| package dekun.wang.spi;
import dekun.wang.spi.interfaces.Command;
import dekun.wang.spi.interfaces.dubbo.CommandDubbo;
import org.apache.dubbo.common.extension.ExtensionLoader;
import org.apache.dubbo.rpc.model.ApplicationModel;
public class TestDubboSpi {
public static void main(String[] args) {
ExtensionLoader<Command> extensionLoader = ExtensionLoader.getExtensionLoader(Command.class);
extensionLoader.getExtension("CommandWhichGit").execute();
extensionLoader.getExtension("CommandEnv").execute();
ExtensionLoader.getExtensionLoader(CommandDubbo.class).getExtension("CommandDubboImpl").execute();
ApplicationModel applicationModel = ApplicationModel.defaultModel();
ExtensionLoader<Command> extensionLoader1 = applicationModel.getExtensionDirector().getExtensionLoader(Command.class);
extensionLoader1.getExtension("CommandWitchLs").execute();
}
}
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| ==========================
/usr/local/bin/git
--------------------------
==========================
Brew=/usr/local/bin:/usr/local/sbin
--------------------------
============CommandDubboImpl================
==========================
/bin/ls
--------------------------
|