層層遞進Struts1（一）之由Servlet引入Struts

在說Struts1之前，我們先來使用Servlet編寫一個程序從而了解Struts產生原因和用途：一個簡單的增刪 改查，我們來看一下使用Servlet是如何實現的，為了形象說明，我們從最基本的開始寫，然後逐步遞進。

第一版

這一版我們使用最常規的做法，增刪改查每個功能都使用自己的Servlet，內容如下：

文件樹

index.jsp

<form 

action="servlet/AddUserServlet" method="post">  
    姓名：<input type="text" name="username" /><br/>  
    <input type="submit" value="submit"/>   
</form>

Servlet

為了方便說明此處的四個Servlet內容基本相同，此處以 AddUserServlet和DelServlet為例：

AddUserServlet

package com.tgb.struts1.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 AddUserServlet extends HttpServlet {  
      
    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response)  
            throws ServletException, IOException {  
            String username=request.getParameter("username");  
            UserManager userManager=new UserManager();  
            userManager.add(username);  
            request.getRequestDispatcher("/add_success.jsp").forward(request, response);  
    }  
      
    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response)  
            throws ServletException, IOException {  
            doGet(request, response);  
    }  
}

DelUserServlet

package com.tgb.struts1.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 DelUserServlet extends HttpServlet {  
    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response)  
            throws ServletException, IOException {  
            String username=request.getParameter("username");  
            UserManager userManager=new UserManager();  
            userManager.del(username);  
            request.getRequestDispatcher("/del_success.jsp").forward(request, response);  
    }  
    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response)  
            throws ServletException, IOException {  
            doGet(request, response);  
    }  
}

UserManager

模仿邏輯處理層和數據處理層

package com.tgb.struts1.servlet;  
      
import java.util.ArrayList;  
import java.util.List;  
      
public class UserManager {  
    public void add(String username){  
        System.out.println("userManager------->add,username="+username);  
    }  
    public void del(String username){  
        System.out.println("userManager------->del,username="+username);  
    }  
    public void modify(String username){  
        System.out.println("userManager------->modify,username="+username);  
    }  
    public List query(String username){  
        System.out.println("userManager------->query,username="+username);  
        List userList=new ArrayList();  
        userList .add("a");  
        userList.add("b");  
        return userList;  
    }  
}

配置文件

<servlet>  
  <servlet-name>AddUserServlet</servlet-name>  
  <servlet-class>com.tgb.struts1.servlet.AddUserServlet</servlet-class>  
</servlet>  
      
<servlet-mapping>  
  <servlet-name>AddUserServlet</servlet-name>  
  <url-pattern>/servlet/AddUserServlet</url-pattern>  
</servlet-mapping>  
<servlet>  
  <servlet-name>DelUserServlet</servlet-name>  
  <servlet-class>com.tgb.struts1.servlet.DelUserServlet</servlet-class>  
</servlet>  
<servlet-mapping>  
  <servlet-name>DelUserServlet</servlet-name>  
  <url-pattern>/servlet/DelUserServlet</url-pattern>  
</servlet-mapping>  
  <servlet>  
  <servlet-name>ModifyUserServlet</servlet-name>  
  <servlet-class>com.tgb.struts1.servlet.ModifyUserServlet</servlet-class>  
</servlet>  
<servlet-mapping>  
  <servlet-name>ModifyUserServlet</servlet-name>  
  <url-pattern>/servlet/ModifyUserServlet</url-pattern>  
</servlet-mapping>  
<servlet>  
    <servlet-name>QueryUserServlet</servlet-name>  
  <servlet-class>com.tgb.struts1.servlet.QueryUserServlet</servlet-class>  
</servlet>  
<servlet-mapping>  
  <servlet-name>QueryUserServlet</servlet-name>  
  <url-pattern>/servlet/QueryUserServlet</url-pattern>  
</servlet-mapping>

總結

使用這種Servlet方式實現，很容易發現，存在多個問題 ：

配置文件冗余

Servlet文件冗余，隨著功能的增多，Servlet文件越來越多，越難以整理分類

代碼冗余，增刪改查四個功能，需要有相當多的重復代碼，難以維護

第二版

針對上面發現的問題我們繼續修改上面的程序：針對第一版的主要的Servlet問題，然後使 用截取url地址的方式，減少Servlet數量。

文件樹

index.jsp

<form 

action="servlet/addUser.do" method="post">  
    姓名：<input type="text" name="username" /><br/>  
    <input type="submit" value="submit"/>   
</form>

Servlet

package com.tgb.struts1.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;  
import javax.swing.text.html.ListView;  
      
import org.apache.taglibs.standard.extra.spath.Path;  
      
public class TestServlet extends HttpServlet {  
      
    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response)  
            throws ServletException, IOException {  
            //get uri and path  
            String uri=request.getRequestURI();  
            String path=uri.substring(uri.indexOf("/",1),uri.indexOf("."));  
            //get username  
            String username=request.getParameter("username");  
            System.out.println(path);  
            UserManager userManager=new UserManager();  
            //forward to path with path  
            if ("/servlet/addUser".equals(path)) {  
                userManager.add(username);  
                request.getRequestDispatcher("/add_success.jsp").forward(request, response);  
            }else if ("/servlet/delUser".equals(path)) {  
                userManager.del(username);  
                request.getRequestDispatcher("/del_success.jsp").forward(request, response);  
            }else if ("/servlet/modifyUser".equals(path)) {  
                userManager.modify(username);  
                request.getRequestDispatcher("/modify_success.jsp").forward(request, response);  
            }else if ("/servlet/queryUser".equals(path)) {  
            List userList=  userManager.query(username);  
            request.setAttribute("userList", userList);  
                request.getRequestDispatcher("/query_success.jsp").forward(request, response);  
            }else {  
                throw new RuntimeException("not found this order!");  
            }  
    }  
    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response)  
            throws ServletException, IOException {  
            doGet(request, response);  
    }  
}

UserManager

同第一版

配置文件

<servlet>  
  <servlet-name>TestServlet</servlet-name>  
  <servlet-class>com.tgb.struts1.servlet.TestServlet</servlet-class>  
</servlet>  
<servlet-mapping>  
  <servlet-name>TestServlet</servlet-name>  
  <url-pattern>*.do</url-pattern>  
</servlet-mapping>

總結

第二版克服了Servlet文件過多、配置冗余和代碼冗余的問 題，但是這個版本的問題也很明顯：TestServlet中代碼重復，最大的一個問題就是：失去了靈活性，在 TestServlet中，使用過多字符串，無法再靈活添加其它功能，已經被我們“寫死”到代碼中。

第三 版

這一版我們嘗試對第二版進行精簡，增加它的靈活性。

文件樹

index.jsp

與 第二版相同

Servlet

package com.tgb.struts1.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;  
import javax.swing.text.html.ListView;  
      
import org.apache.taglibs.standard.extra.spath.Path;  
      
public class TestServlet extends HttpServlet {  
      
    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response)  
            throws ServletException, IOException {  
        //get uri  
            String uri=request.getRequestURI();  
            String path=uri.substring(uri.indexOf("/",1),uri.indexOf("."));  
                  
            String username=request.getParameter("username");  
            System.out.println(path);  
            UserManager userManager=new UserManager();  
            String forward=null;   
            Action action=null;  
            if ("/servlet/addUser".equals(path)) {  
                action=new AddUserAction();  
            }else if ("/servlet/delUser".equals(path)) {  
                action=new DelUserAction();  
            }else if ("/servlet/modifyUser".equals(path)) {  
                action=new ModifyUserAction();  
            }else if ("/servlet/queryUser".equals(path)) {  
                action=new QueryUserAction();  
            }else {  
                throw new RuntimeException("not found this order!");  
            }  
            forward=action.execute(request, response);  
            request.getRequestDispatcher(forward).forward(request, response);  
    }  
      
    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response)  
            throws ServletException, IOException {  
            doGet(request, response);  
    }  
      
}

Action

package com.tgb.struts1.servlet;  
      
import javax.servlet.http.HttpServletRequest;  
import javax.servlet.http.HttpServletResponse;  
      
public interface Action {  
    public String execute(HttpServletRequest request,HttpServletResponse response);   
}

AddUserAction

package com.tgb.struts1.servlet;  
      
import javax.servlet.http.HttpServletRequest;  
import javax.servlet.http.HttpServletResponse;  
      
public class AddUserAction implements Action {  
      
    public String execute(HttpServletRequest request,  
            HttpServletResponse response) {  
        String username=request.getParameter("username");  
        UserManager userManager=new UserManager();  
        userManager.add(username);  
        return "/add_success.jsp";  
    }  
      
}

UserManager

與第一版相同

配置文件    與第二版相同

總結

這一版使用接口和實現接口的類，在一定程度上精簡了Servlet的代碼重復問題，同時也在一定程度上解決了 Servlet中寫的代碼“太死”的問題，但是在擴展性上還是有很大的問題。

總結

從上面的三個 版本中，我們抽象一下，在控制頁面跳轉中，我們需要解決冗余和靈活問題，都需要做些什麼？很明顯根據第 二版，我們知道在控制轉向的方向問題上我們可以使用url截取；結合第三版，我們知道在精簡頁面轉向類中 ，接口可以讓代碼更精簡。再結合以前所學，要使程序更靈活，當然還要把轉向信息寫到配置文件中。

我們再來抽象一下轉向的過程：轉向請求截取，轉向請求分析比對，對請求的數據和邏輯處理，跳轉 到指定頁……好吧，這些基本上已經是Struts1框架的基本內容。