自己动手写MVC框架

对于一个MVC框架来说，最重要的就是C了，特别是前端控制器。前端控制器首先要根据URL请求，来分发该请求应该由哪个controller中哪个方法来处理；然后controller处理完后，还要根据其返回值，最终定位要应该返回哪张视图给客户端，如图：

为些我们实现一个MVC框架主要就是实现这个前端控制器。我写了一个很简单的MVC框架，我将代码分享给大家。

由于工程是由maven搭建的，则pom.xml如下：

（其中jetty也配置好）

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/maven-v4_0_0.xsd">
  <modelVersion>4.0.0</modelVersion>
  <groupId>com.cloud.mvc</groupId>
  <artifactId>mvc-framework</artifactId>
  <packaging>war</packaging>
  <version>0.0.1-SNAPSHOT</version>
  <name>mvc-framework Maven Webapp</name>
  <url>http://maven.apache.org</url>
  <dependencies>
    <dependency>
      <groupId>junit</groupId>
      <artifactId>junit</artifactId>
      <version>3.8.1</version>
      <scope>test</scope>
    </dependency>
    <dependency>
      <groupId>javax.servlet</groupId>
      <artifactId>servlet-api</artifactId>
      <version>2.5</version>
    </dependency>
  </dependencies>
  <build>
    <finalName>mvc-framework</finalName>
    <plugins>
      <plugin>   
        <groupId>org.mortbay.jetty</groupId>
        <artifactId>maven-jetty-plugin</artifactId>
        <version>6.1.10</version>
         <configuration>
            <contextPath>/test</contextPath>
            <connectors>      
                <connector implementation="org.mortbay.jetty.nio.SelectChannelConnector">
                    <port>8080</port>
                </connector>
            </connectors>
            <scanIntervalSeconds>3</scanIntervalSeconds>
         </configuration>
      </plugin>
    </plugins>
  </build>
</project>

 如果要使用我这个框架，则工程目录下必需要有一个mvc.xml文件，而且文件名必需是mvc.xml。该文件的作用和struts2框架中的struts.xml的作用类似。

<?xml version="1.0" encoding="UTF-8"?>
<mvc>
    <action name="user/select" class="com.cloud.mvc.controller.UserController" method="select">
        <result name="success">/WEB-INF/view/index.jsp</result>
        <result name="faild">/index.jsp</result>
    </action>
</mvc>

 两个用于封装配置信息的类。

ActionConfig.java

package com.cloud.mvc.config;

import java.util.HashMap;
import java.util.Map;

public class ActionConfig {
    private String name;
    private String clazz;
    private String method;
    private Map<String, ResultConfig> result;

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getClazz() {
        return clazz;
    }

    public void setClazz(String clazz) {
        this.clazz = clazz;
    }

    public String getMethod() {
        return method;
    }

    public void setMethod(String method) {
        this.method = method;
    }

    public Map<String, ResultConfig> getResult() {
        return result;
    }

    public void setResult(Map<String, ResultConfig> result) {
        this.result = result;
    }

    public ActionConfig() {
    }

    public ActionConfig(String name, String clazz, String method) {
        this.name = name;
        this.clazz = clazz;
        this.method = method;
        this.result = new HashMap<String, ResultConfig>();
    }
}

 ResultConfig.java

package com.cloud.mvc.config;

public class ResultConfig {
    private String name;
    private String content;

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getContent() {
        return content;
    }

    public void setContent(String content) {
        this.content = content;
    }

    public ResultConfig() {
    }

    public ResultConfig(String name, String content) {
        this.name = name;
        this.content = content;
    }
}

 用到的工具类。

XMLUtil.java

package com.cloud.mvc.util;

import java.io.InputStream;
import java.util.HashMap;
import java.util.Map;

import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;

import org.w3c.dom.Document;
import org.w3c.dom.Element;
import org.w3c.dom.NamedNodeMap;
import org.w3c.dom.Node;
import org.w3c.dom.NodeList;

import com.cloud.mvc.config.ActionConfig;
import com.cloud.mvc.config.ResultConfig;

public class XMLUtil {

    public static Map<String, ActionConfig> parseConfig() throws Exception {
        Map<String, ActionConfig> actionConfigs = new HashMap<String, ActionConfig>();
        DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();
        DocumentBuilder db = dbf.newDocumentBuilder();

        InputStream in = XMLUtil.class.getClassLoader().getResourceAsStream("mvc.xml");
        Document document = db.parse(in);
        Element root = document.getDocumentElement();
        NodeList actionNodes = root.getChildNodes();
        for (int i = 0; i < actionNodes.getLength(); i++) {
            Node action = actionNodes.item(i);
            if (null != action && action.getNodeType() == Node.ELEMENT_NODE) {
                NamedNodeMap nodeMaps = action.getAttributes();
                String actionName = nodeMaps.getNamedItem("name").getNodeValue();
                String actionClass = nodeMaps.getNamedItem("class").getNodeValue();
                String actionMethod = nodeMaps.getNamedItem("method").getNodeValue();
                ActionConfig actionConfig = new ActionConfig(actionName, actionClass, actionMethod);

                NodeList resultNodes = action.getChildNodes();
                for (int j = 0; j < resultNodes.getLength(); j++) {
                    Node result = resultNodes.item(j);
                    if (null != result && result.getNodeType() == Node.ELEMENT_NODE) {
                        String resultName = result.getAttributes().getNamedItem("name").getNodeValue();
                        String resultContent = result.getTextContent();

                        ResultConfig resultConfig = new ResultConfig(resultName, resultContent);
                        Map<String, ResultConfig> resultConfigs = actionConfig.getResult();
                        resultConfigs.put(resultName, resultConfig);
                    }
                }
                actionConfigs.put(actionName, actionConfig);
            }
        }
        return actionConfigs;
    }
}

 最为核心的前端控制器。

DispatcherServlet.java

package com.cloud.mvc.servlet;

import java.io.IOException;
import java.lang.reflect.Method;
import java.util.Map;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import com.cloud.mvc.config.ActionConfig;
import com.cloud.mvc.config.ResultConfig;
import com.cloud.mvc.util.XMLUtil;

public class DispatcherServlet extends HttpServlet {
    private static final long serialVersionUID = -1105148104350928967L;
    private Map<String, ActionConfig> actionConfigs;

    @Override
    public void init() throws ServletException {
        super.init();
        try {
            actionConfigs = XMLUtil.parseConfig();
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        this.doPost(req, resp);
    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        String contextPath = req.getContextPath();
        String uri = req.getRequestURI();
        String actionName = uri.substring(contextPath.length() + 1, uri.length());

        ActionConfig actionConfig = actionConfigs.get(actionName);
        String clazz = actionConfig.getClazz();
        String method = actionConfig.getMethod();
        String result = null;
        try {
            Class<?> clazzObject = Class.forName(clazz);
            Method controllerMethod = clazzObject.getMethod(method, HttpServletRequest.class);
            result = (String) controllerMethod.invoke(clazzObject.newInstance(), req);
        } catch (Exception e) {
            e.printStackTrace();
        }
        Map<String, ResultConfig> resultConfigs = actionConfig.getResult();
        String returnPath = resultConfigs.get(result).getContent();
        req.getRequestDispatcher(returnPath).forward(req,resp);
    }

}

 接下来就是将DispatcherServlet类配置到web.xml中。

web.xml

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xmlns="http://java.sun.com/xml/ns/javaee"
    xmlns:web="http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd"
    xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd" id="WebApp_ID" version="3.0">

  <display-name>Archetype Created Web Application</display-name>
    <servlet>
        <servlet-name>mvc</servlet-name>
        <servlet-class>com.cloud.mvc.servlet.DispatcherServlet</servlet-class>
        <init-param>
            <param-name>contextConfigLocation</param-name>
            <param-value>classpath:mvc.xml</param-value>
        </init-param>
        <load-on-startup>1</load-on-startup>
    </servlet>
    <servlet-mapping>
        <servlet-name>mvc</servlet-name>
        <url-pattern>/</url-pattern>
    </servlet-mapping>
</web-app>

 在此只写一个controller类，用于测试。

UserController.java

package com.cloud.mvc.controller;

import javax.servlet.http.HttpServletRequest;

public class UserController {

    public String select(HttpServletRequest req) {
        return "faild";
    }

}

 运行结果：