spring里使用janino进行在线编译

• 一、引入依赖
• 二、新建classloader
• 三、编译并运行java代码

spring-boot-dependencies里已经申明了janino的版本，spring-boot项目直接引入依赖即可

		
			org.codehaus.janino
			janino
		

		// 使用spring boot的LaunchedURLClassLoader作为上级classLoader
		JavaSourceClassLoader classloader = new JavaSourceClassLoader(this.getClass().getClassLoader());

把classloader作为局部变量及时释放，可以在old gc时，回收metaspace里的无用class定义

		// 编译
		String className = "mypackage.B";
		String source = """
				package mypackage;
				import org.slf4j.*;
				public class B implements Runnable {
				    Logger log = LoggerFactory.getLogger(this.getClass());
				    public void run() {
				        log.info("HELLO AAA from {}", this.getClass().getCanonicalName());
				    }
				}
				        """;

		MapResourceFinder map = new MapResourceFinder();
		map.addResource(className.replace(".", "/") + ".java", source);
		classloader.setSourceFinder(map);
		Class dynamicClass = classloader.loadClass(className);
		// 运行
		Runnable runnable = (Runnable) dynamicClass.getDeclaredConstructor().newInstance();
		runnable.run();