JavaWeb之搭建自己的MVC框架（三）

1. 前言

在前两节的内容中，我们完成了一个基本的框架搭建。但是如果我们在前端请求中增加参数，我们要怎么传递到后台方法呢？接下来我们就来研讨这部分内容。

2. 实现

（1）首先我们增加一个新的注解ParamMapping，用来给方法的参数标注其对应的前端参数名称。

package com.mvc.annotation;

import java.lang.annotation.Documented;

import java.lang.annotation.ElementType;

import java.lang.annotation.Retention;

import java.lang.annotation.RetentionPolicy;

import java.lang.annotation.Target;

@Target(ElementType.PARAMETER)

@Retention(RetentionPolicy.RUNTIME)

@Documented

public @interface ParamMapping {

    public String param() default "";

}

（2）我们在SayController中增加一个方法SayAnything，内容如下：

package com.mvc.controller;

import com.mvc.annotation.ParamMapping;

import com.mvc.annotation.URLMapping;

@URLMapping(url="/Say")

public class SayController{

    @URLMapping(url="/Hello")

    public String SayHello(){

        System.out.println("Hello");

        return "Hello";

    }

    @URLMapping(url="/Hi")

    public String SayHi(){

        System.out.println("Hi");

        return "Hi";

    }

    @URLMapping(url="/Anything")

    public String SayAnything(@ParamMapping(param="word") String word){

        System.out.println(word);

        return word;

    }

}

在SayAnything的参数中，我们对String word参数进行了注解@ParamMapping(param="word")，表示将来前端传参数名word，我们的框架会将其对应到SayAnything的String word参数中。

（3）我们在SayController中增加一个方法SayAnything，内容如下：

package com.mvc.controller;

import com.mvc.annotation.ParamMapping;

import com.mvc.annotation.URLMapping;

@URLMapping(url="/Eat")

public class EatController {

    @URLMapping(url="/Apple")

    public String EatApple(){

        System.out.println("I'm eating apples");

        return "Apple";

    }

    @URLMapping(url="/Banana")

    public String EatBanana(){

        System.out.println("I'm eating Banana");

        return "Banana";

    }

    @URLMapping(url="/Anything")

    public String EatAnything(@ParamMapping(param="fruit") String fruit,

                              @ParamMapping(param="cnt") Integer cnt) {

        System.out.println("I'm eating "+fruit+", "+cnt);

        return fruit;

    }

}

EatAnything的参数的注解和SayAnything是同一个道理。

（4）调整ServletCenter，使其完成前端参数到JAVA后台参数的传递过程。

package com.mvc.servlet;

import java.io.IOException;

import java.lang.annotation.Annotation;

import java.lang.reflect.InvocationTargetException;

import java.lang.reflect.Method;

import javax.servlet.ServletException;

import javax.servlet.http.HttpServlet;

import javax.servlet.http.HttpServletRequest;

import javax.servlet.http.HttpServletResponse;

import com.mvc.annotation.ParamMapping;

import com.mvc.base.MVCBase;

import com.mvc.listener.UrlMappingCollection;

public class ServletCenter extends HttpServlet {

    private static final long serialVersionUID = -1163369749078348562L;

    private void doTransfer(HttpServletRequest req, HttpServletResponse resp)

            throws ServletException, IOException, ClassNotFoundException,

                   SecurityException, NoSuchMethodException, IllegalArgumentException,

                   IllegalAccessException, InvocationTargetException,

                   InstantiationException {

        for (MVCBase mvcBase : UrlMappingCollection.getMvcBases()) {

            if (req.getRequestURI().equals(

                         req.getServletContext().getContextPath()+mvcBase.getUrl())) {

                Class<?> clazz = Class.forName(mvcBase.getController());

                Method[] methods = clazz.getMethods();

                for (Method method : methods) {

                    if (method.getName().equals(mvcBase.getMethod())) {

                        //拿到参数类型列表

                        Class<?>[] paramTypes =  method.getParameterTypes();

                        //拿到参数的注解列表

                        Annotation[][] paramAnno = method.getParameterAnnotations();

                        //new一个参数值数组吗，将来调用方法的时候要用

                        Object[] paramValues = new Object[paramTypes.length];

                        //每个参数会形成paramAnno的第一维，每个参数的每个注解会行程paramAnno的第二维

                        //所以paramAnno.length和paramTypes.length是相等的。

                        for (int i=0; i<paramAnno.length; i++) {

                            for (int j=0; j<paramAnno[i].length; j++) {

                                if (paramAnno[i][j] instanceof ParamMapping) {

                                    String paramName = ((ParamMapping) paramAnno[i][j]).param();

                                    if (req.getParameter(paramName) != null) {

                                        if (paramTypes[i].equals(String.class)) {

                                            paramValues[i] = req.getParameter(paramName);

                                        } else if (paramTypes[i].equals(Integer.class)) {

                                            paramValues[i] = Integer.valueOf(

                                                               req.getParameter(paramName));

                                        } else {

                                            //其他类型待后续扩展

                                        }

                                    }

                                }

                            }

                        }

                        method.invoke(clazz.newInstance(), paramValues);

                    }

                }

            }

        }

    }

    @Override

    protected void doGet(HttpServletRequest req, HttpServletResponse resp)

                           throws ServletException, IOException {

        try {

            doTransfer(req, resp);

        } catch (Exception e) {

            System.out.println(e.toString());

        }

    }

    @Override

    protected void doPost(HttpServletRequest req, HttpServletResponse resp)

                            throws ServletException, IOException {

        try {

            doTransfer(req, resp);

        } catch (Exception e) {

            System.out.println(e.toString());

        }

    }

}

3. 测试效果：

启动tomcat，在浏览器中输入：

可以看到控制台打印出：

12345678
I'm eating 1234, 2

巴特西