JAVA使用ServiceLoader加载服务
https://blog.csdn.net/jianggujin/article/details/81030983
serviceLoader就是spi的一种实现，spi服务的提供者接口也就是spi service provider interface
主要是创建一个接口让第三方框架去实现，比如jdbc.driver这个可以被mysql，oracle，SQLServer去实现
还有像日志logger，有slf4j
版权声明：本文为博主原创文章，转载请标明出处。 https://blog.csdn.net/jianggujin/article/details/81030983
ServiceLoader是SPI的是一种实现，所谓SPI，即Service Provider Interface，用于一些服务提供给第三方实现或者扩展，可以增强框架的扩展或者替换一些组件。
其实关于ServiceLoader，我们平时虽然很少用到，但是却在背后为我们做了很多事情，最常见的就是JDBC的操作了，相信大家对DriverManager类并不陌生，我们可以通过该类加载驱动并获得数据库连接，在这个类中其实就用到了ServiceLoader。
private static void loadInitialDrivers() {
String drivers;
try {
drivers = AccessController.doPrivileged(new PrivilegedAction<String>() {
public String run() {
return System.getProperty("jdbc.drivers");
}
});
} catch (Exception ex) {
drivers = null;
}
// If the driver is packaged as a Service Provider, load it.
// Get all the drivers through the classloader
// exposed as a java.sql.Driver.class service.
// ServiceLoader.load() replaces the sun.misc.Providers()
AccessController.doPrivileged(new PrivilegedAction<Void>() {
public Void run() {
ServiceLoader<Driver> loadedDrivers = ServiceLoader.load(Driver.class);
Iterator<Driver> driversIterator = loadedDrivers.iterator();
/* Load these drivers, so that they can be instantiated.
* It may be the case that the driver class may not be there
* i.e. there may be a packaged driver with the service class
* as implementation of java.sql.Driver but the actual class
* may be missing. In that case a java.util.ServiceConfigurationError
* will be thrown at runtime by the VM trying to locate
* and load the service.
*
* Adding a try catch block to catch those runtime errors
* if driver not available in classpath but it's
* packaged as service and that service is there in classpath.
*/
try{
while(driversIterator.hasNext()) {
driversIterator.next();
}
} catch(Throwable t) {
// Do nothing
}
return null;
}
});
println("DriverManager.initialize: jdbc.drivers = " + drivers);
if (drivers == null || drivers.equals("")) {
return;
}
String[] driversList = drivers.split(":");
println("number of Drivers:" + driversList.length);
for (String aDriver : driversList) {
try {
println("DriverManager.Initialize: loading " + aDriver);
Class.forName(aDriver, true,
ClassLoader.getSystemClassLoader());
} catch (Exception ex) {
println("DriverManager.Initialize: load failed: " + ex);
}
}
}
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接下来我们就还看看如何使用ServiceLoader，假设我们需要一个日志的服务，那么首先我们需要定义一个服务的接口
package com.jinggujin.service;
public interface LogService {
void log(String msg);
}
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针对这个服务我们再来提供一个实现
package com.jinggujin.service;
public class DefaultLogService implements LogService {
@Override
public void log(String msg) {
System.out.println(msg);
}
}
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好了下面我们需要提供我们的服务，我们需要在META-INF中添加services文件夹，然后在该文件夹中创建一个文件，文件名为服务接口的全限定类名，那么这里完整的文件路径应为：META-INF/services/com.jinggujin.service.LogService，最后我们需要在该文件中添加服务实现的全限定类名，一行数据一个实现全限定类名，文件内容如下：
com.jinggujin.service.DefaultLogService
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准备工作已经完成，我们就来使用ServiceLoader加载我们提供的服务。
package test;
import java.util.ServiceLoader;
import org.junit.Test;
import com.jinggujin.service.LogService;
public class ServiceLoaderTest {
@Test
public void test() {
ServiceLoader<LogService> loader = ServiceLoader.load(LogService.class);
for (LogService service : loader) {
System.out.println(service.getClass());
}
}
}
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作者：蒋固金
来源：CSDN
原文：https://blog.csdn.net/jianggujin/article/details/81030983
版权声明：本文为博主原创文章，转载请附上博文链接！