Spring6.0从入门到精通-RuntimeHints

RuntimeHints

假如应用中有如下代码：

/**
* 作者：周瑜大都督
*/
public class ZhouyuService {

    public string test(){
        return "zhouyu";
    }
}

@Component
public class UserService {

    public String test(){

        String result = "";
        try {
            Method test = ZhouyuService.class.getMethod("test", null);
            result = (String) test.invoke(ZhouyuService.class.newInstance(), null);
        } catch (NoSuchMethodException e) {
            throw new RuntimeException(e);
        } catch (InvocationTargetException e) {
            throw new RuntimeException(e);
        } catch (IllegalAccessException e) {
            throw new RuntimeException(e);
        } catch (InstantiationException e) {
            throw new RuntimeException(e);
        }

        return result;
    }

}

在UserService中，通过反射的方式使用到了ZhouyuService的无参构造方法（ZhouyuService.class.newInstance()），如果我们不做任何处理，那么打成二进制可执行文件后是运行不了的，可执行文件中是没有ZhouyuService的无参构造方法的，会报如下错误：

我们可以通过Spring提供的Runtime Hints机制来间接的配置reflect-config.json。

方式一：RuntimeHintsRegistrar

提供一个RuntimeHintsRegistrar接口的实现类，并导入到Spring容器中就可以了：

@Component
@ImportRuntimeHints(UserService.ZhouyuServiceRuntimeHints.class)
public class UserService {

    public String test(){

        String result = "";
        try {
            Method test = ZhouyuService.class.getMethod("test", null);
            result = (String) test.invoke(ZhouyuService.class.newInstance(), null);
        } catch (NoSuchMethodException e) {
            throw new RuntimeException(e);
        } catch (InvocationTargetException e) {
            throw new RuntimeException(e);
        } catch (IllegalAccessException e) {
            throw new RuntimeException(e);
        } catch (InstantiationException e) {
            throw new RuntimeException(e);
        }


        return result;
    }

    static class ZhouyuServiceRuntimeHints implements RuntimeHintsRegistrar {

        @Override
        public void registerHints(RuntimeHints hints, ClassLoader classLoader) {
            try {
                hints.reflection().registerConstructor(ZhouyuService.class.getConstructor(), ExecutableMode.INVOKE);
            } catch (NoSuchMethodException e) {
                throw new RuntimeException(e);
            }
        }
    }
}

方式二：@RegisterReflectionForBinding

@RegisterReflectionForBinding(ZhouyuService.class)
public String test(){

    String result = "";
    try {
        Method test = ZhouyuService.class.getMethod("test", null);
        result = (String) test.invoke(ZhouyuService.class.newInstance(), null);
    } catch (NoSuchMethodException e) {
        throw new RuntimeException(e);
    } catch (InvocationTargetException e) {
        throw new RuntimeException(e);
    } catch (IllegalAccessException e) {
        throw new RuntimeException(e);
    } catch (InstantiationException e) {
        throw new RuntimeException(e);
    }


    return result;
}

注意

如果代码中的methodName是通过参数获取的，那么GraalVM在编译时就不能知道到底会使用到哪个方法，那么test方法也要利用RuntimeHints来进行配置。

@Component
@ImportRuntimeHints(UserService.ZhouyuServiceRuntimeHints.class)
public class UserService {

    public String test(){

        String methodName = System.getProperty("methodName");

        String result = "";
        try {
            Method test = ZhouyuService.class.getMethod(methodName, null);
            result = (String) test.invoke(ZhouyuService.class.newInstance(), null);
        } catch (NoSuchMethodException e) {
            throw new RuntimeException(e);
        } catch (InvocationTargetException e) {
            throw new RuntimeException(e);
        } catch (IllegalAccessException e) {
            throw new RuntimeException(e);
        } catch (InstantiationException e) {
            throw new RuntimeException(e);
        }


        return result;
    }

    static class ZhouyuServiceRuntimeHints implements RuntimeHintsRegistrar {

        @Override
        public void registerHints(RuntimeHints hints, ClassLoader classLoader) {
            try {
                hints.reflection().registerConstructor(ZhouyuService.class.getConstructor(), ExecutableMode.INVOKE);
                hints.reflection().registerMethod(ZhouyuService.class.getMethod("test"), ExecutableMode.INVOKE);
            } catch (NoSuchMethodException e) {
                throw new RuntimeException(e);
            }
        }
    }
}

或者使用了JDK动态代理：

public String test() throws ClassNotFoundException {

    String className = System.getProperty("className");
	Class<?> aClass = Class.forName(className);

	Object o = Proxy.newProxyInstance(UserService.class.getClassLoader(), new Class[]{aClass}, new InvocationHandler() {
    	@Override
    	public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
        	return method.getName();
    	}
	});

	return o.toString();
}

那么也可以利用RuntimeHints来进行配置要代理的接口：

public void registerHints(RuntimeHints hints, ClassLoader classLoader) {
    hints.proxies().registerJdkProxy(Userinterface.class);
}

方式三：@Reflective

对于反射用到的地方，我们可以直接加一个@Reflective，前提是ZhouyuService得是一个bean：

@Component
public class ZhouyuService {

    @Reflective
    public ZhouyuService() {
    }

    @Reflective
    public String test(){
        return "zhouyu";
    }
}

以上Spring6提供的RuntimeHints机制，我们可以使用该机制更方便的告诉GraalVM我们额外用到了哪些类、接口、方法等信息，最终Spring会生成对应的reflect-config.json、proxy-config.json中的内容，GraalVM就知道了。