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struts（一）——jsp+Servlet講解MVC框架基本原理

編輯：關於JSP

自從接觸java一來，經常在論壇上看到一些大牛談論框架雲雲，每每都覺得他們這些懂框架的都是真的大牛啊。羨慕嫉妒恨不能當飯吃，咱也跟隨巨人的步伐，開始研究框架之旅。struts是所有框架中最簡單、最經典的，從struts開始入手，算是一步捷徑。

本篇作為預備篇，先從緣起緣滅開始吧——MVC基本原理。

MVC框架3個部分間的功能協作過程，已經很清楚了，不過這裡可以再簡單提一下：

擇顯示這些數據的相應的視圖，並將視圖返回給用戶。

1、終端用戶發出一個請求，該請求到達Controller控制器。

2、控制器接受請求後，會檢查該請求，然後決定使用什麼業務邏輯來處理該請求，這時控制器會將該請求轉發給一個相應的業務邏輯去處理；

3、模型中包含處理該用戶請求的所有業務組件，並且也執行用戶所需要的全部數據存取，代表終端用戶查詢檢索出的任何數據都被打包返回給控制器。

4、控制器接受從模型返回的數據，並選
下面，先來采用一個不靈活的Servlet進行實現：

[java]
package com.xxjstgb.servlet;
import java.io.IOException;
import java.util.List;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
public class TestServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        String requestURI = request.getRequestURI();
                int start=requestURI.indexOf("/",1);
                int end=requestURI.indexOf(".");
                String path=requestURI.substring(start,end);
                System.out.println("path=" + path);
        String username = request.getParameter("username");
        UserManager userManager = new UserManager();
        String forward = "";
        if ("/servlet/delUser".equals(path)) {
            userManager.del(username);
            forward = "/del_success.jsp";
        }else if ("/servlet/addUser".equals(path)) {
            userManager.add(username);
            forward = "/add_success.jsp";
        }else if ("/servlet/modifyUser".equals(path)) {
            userManager.modify(username);
            forward = "/modify_success.jsp";
        }else if ("/servlet/queryUser".equals(path)) {
            List userList = userManager.query(username);
            request.setAttribute("userList", userList);
            forward = "/query_success.jsp";
        }else {
            throw new RuntimeException("請求失敗");
        }
        request.getRequestDispatcher(forward).forward(request, response);
       }
}

package com.xxjstgb.servlet;
import java.io.IOException;
import java.util.List;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
public class TestServlet extends HttpServlet {
@Override
protected void doGet(HttpServletRequest request, HttpServletResponse response)
   throws ServletException, IOException {
  String requestURI = request.getRequestURI();
                int start=requestURI.indexOf("/",1);
                int end=requestURI.indexOf(".");
                String path=requestURI.substring(start,end);
                System.out.println("path=" + path);
  String username = request.getParameter("username");
  UserManager userManager = new UserManager();
  String forward = "";
  if ("/servlet/delUser".equals(path)) {
   userManager.del(username);
   forward = "/del_success.jsp";
  }else if ("/servlet/addUser".equals(path)) {
   userManager.add(username);
   forward = "/add_success.jsp";
  }else if ("/servlet/modifyUser".equals(path)) {
   userManager.modify(username);
   forward = "/modify_success.jsp";
  }else if ("/servlet/queryUser".equals(path)) {
   List userList = userManager.query(username);
   request.setAttribute("userList", userList);
   forward = "/query_success.jsp";
  }else {
   throw new RuntimeException("請求失敗");
  }
  request.getRequestDispatcher(forward).forward(request, response);
       }
}

配置文件：

[html]
<?xml version="1.0" encoding="UTF-8"?>
<web-app version="2.4"
    xmlns="http://java.sun.com/xml/ns/j2ee"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://java.sun.com/xml/ns/j2ee
    http://java.sun.com/xml/ns/j2ee/web-app_2_4.xsd">

    <servlet>
        <servlet-name>TestServlet</servlet-name>
        <servlet-class>com.xxjstgb.servlet.testServlet</servlet-class>
    </servlet>
     <servlet-mapping>
        <servlet-name>TestServlet</servlet-name>
        <url-pattern>*.do</url-pattern>
     </servlet-mapping>
</web-app>

<?xml version="1.0" encoding="UTF-8"?>
<web-app version="2.4"
xmlns="http://java.sun.com/xml/ns/j2ee"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://java.sun.com/xml/ns/j2ee
http://java.sun.com/xml/ns/j2ee/web-app_2_4.xsd">

<servlet>
<servlet-name>TestServlet</servlet-name>
<servlet-class>com.xxjstgb.servlet.testServlet</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>TestServlet</servlet-name>
<url-pattern>*.do</url-pattern>
</servlet-mapping>
</web-app>

當用戶發出請求時（比如請求為：http://localhost:8080/struts_dispatchaction/servlet/delUser.do），根據用戶請求的具有一定特點的URL（該URL以/servlet/開頭或者是*.do結尾），訪問到相應的Servlet。

根據配置文件可知：這裡配置的是以".do"結尾的請求，都能夠訪問到TestServlet。該Servlet又截取了每個請求中特有的部分"/servlet/delUser"，根據這個串兒，調用相應的業務邏輯，並作相應的轉向。

不過這種實現方式，大家一看便會覺得很不妥，這個Servlet的任務太重了。在這裡調用了模型層邏輯，同時也進行了所有的頁面轉向。另外，包含了大量的if…else語句，由於業務的不穩定性，這裡如果經常需要添加或者刪除else語句的話，這將是一個非常糟糕的設計。

下面改良設計，我們將控制器細化為前端控制器TestServlet和業務控制器Action。

前端控制器有兩個任務：1、根據一定規則，截取url；2、根據url分發到相應的Action。

業務控制器負責：1、接受表單數據；2、調用業務邏輯；3、返回轉向信息。

Action：

[java]
package com.xxjstgb.servlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
public interface Action {
public String execute(HttpServletRequest request, HttpServletResponse response)
throws Exception;
}

package com.xxjstgb.servlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
public interface Action {
public String execute(HttpServletRequest request, HttpServletResponse response)
throws Exception;
}
delUserActiion：

[java]
package com.xxjstgb.servlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
public class DelUserAction implements Action {
    public String execute(HttpServletRequest request,
            HttpServletResponse response) throws Exception {
                //接收表單參數
                String username = request.getParameter("username");
        //調用業務邏輯
        UserManager userManager = new UserManager();
        try {
            userManager.del(username);
        }catch(Exception e) {
            return "del_error.jsp"; //轉向路徑可以通過配置文件讀取
        }
                //轉向信息
                return "/del_success.jsp"; //轉向路徑可以通過配置文件讀取
    }
}

package com.xxjstgb.servlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
public class DelUserAction implements Action {
public String execute(HttpServletRequest request,
   HttpServletResponse response) throws Exception {
                //接收表單參數
                String username = request.getParameter("username");
  //調用業務邏輯
  UserManager userManager = new UserManager();
  try {
   userManager.del(username);
  }catch(Exception e) {
   return "del_error.jsp"; //轉向路徑可以通過配置文件讀取
  }
                //轉向信息
                return "/del_success.jsp"; //轉向路徑可以通過配置文件讀取
}
}

改良設計後的TestServlet：

[java]
package com.xxjstgb.servlet;
import java.io.IOException;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
public class TestServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        String requestURI=request.getRequestURI();
        int start=requestURI.indexOf("/",1);
        int end=requestURI.indexOf(".");
        String path=requestURI.substring(start,end);
        Action action = null;
        if ("/servlet/delUser".equals(path)) {
            action = new DelUserAction();
        }else if ("/servlet/addUser".equals(path)) {
            action = new AddUserAction();
        }else if ("/servlet/modifyUser".equals(path)) {
            action = new ModifyUserAction();
        }else if ("/servlet/queryUser".equals(path)) {
            action = new QueryUserAction();
        }else {
            throw new RuntimeException("請求失敗");
        }
        String forward = null;
        try {
            forward = action.execute(request, response);
        } catch (Exception e) {
            e.printStackTrace();
        }
        request.getRequestDispatcher(forward).forward(request, response);
    }
}

package com.xxjstgb.servlet;
import java.io.IOException;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
public class TestServlet extends HttpServlet {
@Override
protected void doGet(HttpServletRequest request, HttpServletResponse response)
   throws ServletException, IOException {
  String requestURI=request.getRequestURI();
  int start=requestURI.indexOf("/",1);
  int end=requestURI.indexOf(".");
  String path=requestURI.substring(start,end);
  Action action = null;
  if ("/servlet/delUser".equals(path)) {
   action = new DelUserAction();
  }else if ("/servlet/addUser".equals(path)) {
   action = new AddUserAction();
  }else if ("/servlet/modifyUser".equals(path)) {
   action = new ModifyUserAction();
  }else if ("/servlet/queryUser".equals(path)) {
   action = new QueryUserAction();
  }else {
   throw new RuntimeException("請求失敗");
  }
  String forward = null;
  try {
   forward = action.execute(request, response);
  } catch (Exception e) {
   e.printStackTrace();
  }
  request.getRequestDispatcher(forward).forward(request, response);
}
}