Spring自定义注解实现Controller获取想要的数据

最近看组内一个哥们写了一个HandlerAdapter，能自动获取Http请求里面的Cookie并组装成一个Model来直接使用。觉得很牛逼。因此自己做了一个，特来分享。

原理：

利用org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter。

在DispatcherServlet里面定义了:

private List<HandlerAdapter> handlerAdapters;

用于Servlet初始化的时候查找配置了的HandlerAdapter。再在Servlet请求到来之时通过调用doService层层调用

	protected HandlerAdapter getHandlerAdapter(Object handler) throws ServletException {
		for (HandlerAdapter ha : this.handlerAdapters) {
			if (logger.isTraceEnabled()) {
				logger.trace("Testing handler adapter [" + ha + "]");
			}
			if (ha.supports(handler)) {
				return ha;
			}
		}
		throw new ServletException("No adapter for handler [" + handler +
				"]: Does your handler implement a supported interface like Controller?");
	}

让它们去处理Handler。此处贴上一种实现代码：

Demo.java:

package com.hp.share.annocation;

public class Demo {

    private int id;
    private String name;
    private byte sex;
    public int getId() {
        return id;
    }
    public void setId(int id) {
        this.id = id;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public byte getSex() {
        return sex;
    }
    public void setSex(byte sex) {
        this.sex = sex;
    }
    public Demo() {
        this.id = 1001;
        this.name = "hello world";
        this.sex = 1;
    }

    @Override
    public String toString() {
        return "Demo [id=" + id + ", name=" + name + ", sex=" + sex + "]";
    }
}

DemoAnnotation.java:

package com.hp.share.annocation;

import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

@Retention(RetentionPolicy.RUNTIME)
@Target({ ElementType.PARAMETER })
public @interface DemoAnnotation {
}

DemoProcessor.java:

package com.hp.share.handler;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.core.MethodParameter;
import org.springframework.web.bind.support.WebDataBinderFactory;
import org.springframework.web.context.request.NativeWebRequest;
import org.springframework.web.method.support.HandlerMethodArgumentResolver;
import org.springframework.web.method.support.ModelAndViewContainer;

import com.hp.share.annocation.Demo;
import com.hp.share.annocation.DemoAnnotation;

public class DemoProcessor implements HandlerMethodArgumentResolver {

    private static Logger logger = LoggerFactory.getLogger(DemoProcessor.class);

    public boolean supportsParameter(MethodParameter parameter) {
        boolean res = parameter.getParameterAnnotation(DemoAnnotation.class) != null;
        logger.info("开始校验 : {}", res);
        return res;
    }

    public Object resolveArgument(MethodParameter parameter, ModelAndViewContainer mavContainer,
            NativeWebRequest webRequest, WebDataBinderFactory binderFactory) throws Exception {
        logger.info("这是注解执行的标志~~~");
        return new Demo();
    }
}

DemoController.java:

package com.hp.share.controller;

import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.ResponseBody;

import com.google.common.base.Preconditions;
import com.hp.share.annocation.Demo;
import com.hp.share.annocation.DemoAnnotation;

@Controller
public class DemoController {

    @RequestMapping("/hello")
    @ResponseBody
    public String demo(@DemoAnnotation Demo req) {

        Preconditions.checkNotNull(req);
        System.out.println(String.valueOf(req));

        return "success";
    }
}

需要配置:

	<bean
		class="org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter">
		<property name="customArgumentResolvers">
			<list>
				<bean class="com.hp.share.handler.DemoProcessor" />
			</list>
		</property>
	</bean>
	<mvc:annotation-driven />

此处切记<mvc:annotation-driven />并且它得在所有bean的下面。如果你配置了AnnotationMethodHandlerAdapter，就更应该将其放在配置的最后面了。

具体原因可查看Spring源码(跟DispatcherServlet即可)

如果测试时发现自己的代码不好使，可debug  DispatcherServlet。多半是因为【配置出错或者是HandlerAdapter引用错误(还是配置错误)

就这样，就可以轻轻松松的获取到自己自定义注解的内容了。如果想对Method进行注解，依然可以使用这个类的，详情可查看源码。