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Detailed explanation of struts1 simple mvc graphic code example

黄舟Original: 2017-09-05 10:37:081276browse

This article mainly introduces the relevant information of the simple mvc example of struts1. Friends who need it can refer to it

First look at the MVC pattern flow chart (in fact, the MVC design pattern is model2 in java.):

As shown in the figure, the C layer is mainly the Servlet layer that controls page jumps, the M layer is the specific business processing logic, and JSP is the so-called V layer. MVC is different from the three layers we usually call UI layer, BLL layer, and DAL layer. The specific differences are as follows:

As can be seen from the figure, JSP and Servlet constitute the UI layer, and the Model layer is divided into the BLL layer and the DAL layer (that is, the business logic and data persistence layer).

After theoretically understanding the MVC design pattern, let’s start typing a sample code of the MVC design pattern:

JSP index page index.jsp:

<%@ page language="java" contentType="text/html; charset=GB18030" 
 pageEncoding="GB18030"%> 
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> 
<html> 
<head> 
<meta http-equiv="Content-Type" content="text/html; charset=GB18030"> 
<title>Insert title here</title> 
</head> 
<body> 
 <form action="servlet/addUser.action" method="post"> 
  姓名：<input type="text" name="username" > 
  <input type="submit" value="提交"> 
 </form> 
  
</body> 
</html>

with business logic code UserManager:

package com.bjpowernode.servlet; 
 
import java.util.ArrayList; 
import java.util.List; 
 
public class UserManager { 
  
 public void addUser(String username){ 
  System.out.println("UserManager.addUsre()--->username:"+username); 
 } 
  
 public void delUser(String username){ 
  System.out.println("UserManager.delUser()--->username:"+username); 
 } 
  
 public void modifyUser(String username){ 
  System.out.println("UserManager.modifyUser()--->username"+username); 
 } 
  
 public List queryUser(String username){ 
  System.out.println("UserManager.queryUser()--->username"+username); 
  List userList=new ArrayList(); 
  userList.add("a"); 
  userList.add("b"); 
  userList.add("c"); 
  return userList; 
 } 
}

with Servlet control code:

package com.bjpowernode.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 { 
 
  
 protected void doGet(HttpServletRequest request, HttpServletResponse response) 
   throws ServletException, IOException { 
   
  String requestURI=request.getRequestURI(); 
  System.out.println("request="+requestURI); 
  String path=requestURI.substring(requestURI.indexOf("/",1),requestURI.indexOf(".")); 
  System.out.println("path="+path); 
   
  String username=request.getParameter("username"); 
  UserManager userManager=new UserManager(); 
  //userManager.addUser(username); 
  String forward=""; 
  if("/servlet/delUser".equals(path)){ 
   userManager.delUser(username); 
   forward="/del_success.jsp"; 
  }else if("/servlet/addUser".equals(path)){ 
   userManager.addUser(username); 
   forward="/add_success.jsp"; 
  }else if("/servlet/modifyUser".equals(path)){ 
   userManager.modifyUser(username); 
   forward="/modify_success.jsp"; 
  }else if("/servlet/queryUser".equals(path)){ 
   List userList=userManager.queryUser(username); 
   request.setAttribute("userList", userList); 
   forward="/query_success.jsp"; 
  }else{ 
   throw new RuntimeException("请求失败"); 
  } 
  request.getRequestDispatcher(forward).forward(request, response); 
 
}

The main function of this servlet code is to determine which page requests the server to perform those operations, and then calls the business logic to implement the corresponding business operations.

Configure Servlet:

<?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>test_Servlet</display-name> 
 <welcome-file-list> 
 <welcome-file>index.html</welcome-file> 
 <welcome-file>index.htm</welcome-file> 
 <welcome-file>index.jsp</welcome-file> 
 <welcome-file>default.html</welcome-file> 
 <welcome-file>default.htm</welcome-file> 
 <welcome-file>default.jsp</welcome-file> 
 </welcome-file-list> 
 
 <servlet> 
 <servlet-name>TestServlet</servlet-name> 
 <servlet-class>com.cjq.servlet.TestServlet</servlet-class> 
 </servlet> 
 <servlet-mapping> 
 <servlet-name>TestServlet</servlet-name> 
 <url-pattern>*.action</url-pattern> 
 </servlet-mapping> 
 
 
</web-app>

Output result:

## Through the above example You already have a preliminary understanding of the MVC design pattern. In fact, this example is the basis for learning the Struts framework. Only by understanding this example can you understand the implementation principle of the Struts framework and the use of the Struts framework.

So how can we introduce the Struts framework through this example? This problem starts with IF-Eles.

First of all, we saw that there are many if-else statements in TestServlet. This is very unstable. Such a program is very inflexible. If there are changes in the future, the maintenance will be very poor. ; Moreover, we have a large number of strings in if-else, which will cause writing errors during coding, which will cause trouble for debugging. Therefore, removing if-else has become the first step in our reconstruction and the first step in our learning of the Struts framework. Because the If-Else statement block appears in TestServlet, the program becomes less flexible and clumsy when responding to changes in requirements. So I will continue the previous article to reconstruct the TestServlet code, mainly using inheritance polymorphism to further reconstruct the TestServlet.

The following enters the reconstruction stage:

package com.bjpowernode.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 {

 
 protected void doGet(HttpServletRequest request, HttpServletResponse response)
 throws ServletException, IOException {
 
 String requestURI=request.getRequestURI();
 System.out.println("request="+requestURI);
 String path=requestURI.substring(requestURI.indexOf("/",1),requestURI.indexOf("."));
 System.out.println("path="+path);
 
 String username=request.getParameter("username");
 UserManager userManager=new UserManager();
 //userManager.addUser(username);
 String forward="";
 if("/servlet/delUser".equals(path)){
 userManager.delUser(username);
 forward="/del_success.jsp";
 }else if("/servlet/addUser".equals(path)){
 userManager.addUser(username);
 forward="/add_success.jsp";
 }else if("/servlet/modifyUser".equals(path)){
 userManager.modifyUser(username);
 forward="/modify_success.jsp";
 }else if("/servlet/queryUser".equals(path)){
 List userList=userManager.queryUser(username);
 request.setAttribute("userList", userList);
 forward="/query_success.jsp";
 }else{
 throw new RuntimeException("请求失败");
 }
 request.getRequestDispatcher(forward).forward(request, response);
  }
}

First of all, we see that assignment to forward appears in each statement block, which is actually the assignment to the page. The jump path is assigned a value, and the jump path is assigned based on each request path judgment. In addition, there are business processes in each IF-Else statement block. We need to put these business processes into classes to make the responsibilities more unified, which is more in line with the object-oriented idea.

We start refactoring from here. We can encapsulate this jump path and business logic.

Since it is encapsulated, we will abstract an excuse and mainly complete a method. The main function of this method is to complete the business logic encapsulation and path jump return. Then four classes are established to mainly implement the corresponding business processing of additions, deletions, modifications and queries and the jump path return after processing.

The code is as follows:

Interface Action:

package com.bjpowernode.servlet;

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

public interface Action {
 
 public String execute(HttpServletRequest request,HttpServletResponse response)
 throws Exception;
}

Add, delete, modify and check implementation class:

Add user implementation class:

package com.bjpowernode.servlet;

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

public class AddUserAction implements Action {

 
 public String execute(HttpServletRequest request,
 HttpServletResponse response) throws Exception {
 String username=request.getParameter("username");
 UserManager userManager=new UserManager();
 userManager.addUser(username);
 return "/add_success.jsp";
 }

}

Delete user implementation class:

package com.bjpowernode.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 {
 String username=request.getParameter("username");
 UserManager userManager=new UserManager();
 userManager.delUser(username);
 return "/del_success.jsp";
 }

}

Update user implementation class:

package com.bjpowernode.servlet;

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

public class ModifyUserAction implements Action {

 @Override
 public String execute(HttpServletRequest request,
 HttpServletResponse response) throws Exception {
 String username=request.getParameter("username");
 UserManager userManager=new UserManager();
 userManager.modifyUser(username);
 return "/modify_success.jsp";
 }

}

Query user implementation class:

package com.bjpowernode.servlet;

import java.util.List;

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

public class QueryUserAction implements Action {

 @Override
 public String execute(HttpServletRequest request,
 HttpServletResponse response) throws Exception {
 String username=request.getParameter("username");
 UserManager userManager=new UserManager();
 List userList=userManager.queryUser(username);
 request.setAttribute("userList", userList);
 return "/query_success.jsp";
 }

}

TestServlet class The reconstruction is as follows:

package com.bjpowernode.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 {

 
 protected void doGet(HttpServletRequest request, HttpServletResponse response)
 throws ServletException, IOException {
 
 String requestURI=request.getRequestURI();
 System.out.println("request="+requestURI);
 String path=requestURI.substring(requestURI.indexOf("/",1),requestURI.indexOf("."));
 System.out.println("path="+path);
 
 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("请求失败");
 }
 String forward=null;
 try{
 forward=action.execute(request, response);
 }catch(Exception e){
 e.printStackTrace();
 }
 request.getRequestDispatcher(forward).forward(request, response);
  }
}

Running results:

这样TestServlet类虽然没有彻底去掉If-Else，但是这样的代码变得更加简练，利用多肽实现业务逻辑处理和路径跳转返回。职责更加清晰，让维护变得更加轻松。

package com.bjpowernode.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 { 
 
   
  protected void doGet(HttpServletRequest request, HttpServletResponse response) 
      throws ServletException, IOException { 
     
    String requestURI=request.getRequestURI(); 
    System.out.println("request="+requestURI); 
    String path=requestURI.substring(requestURI.indexOf("/",1),requestURI.indexOf(".")); 
    System.out.println("path="+path); 
     
 
    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("请求失败"); 
    } 
    String forward=null; 
    try{ 
      forward=action.execute(request, response); 
    }catch(Exception e){ 
      e.printStackTrace(); 
    } 
    request.getRequestDispatcher(forward).forward(request, response); 
   } 
}

解决字符串问题，当然就要用到配置文件了，用到配置文件就要有用来读取配置文件的相关的类和方法，这里就用dom4j中的类来读取配置文件，这里的配置文件的书写是有点逻辑上的难度的。

我们来看TestServlet中的代码，我们要在这个testservlet中实现读取配置文件和path比较，还有利用多肽实例化相应的实现类，最后通过实例化的实现类的方法来返回跳转路径，最终跳转到相应的页面。

所以我们的配置文件就要不仅配上testservlet中出现的字符串，还要配置相应的Action接口的实现类（我们可以利用反射来实例化该类的对象，进而使用这个类的所有属性和方法），另外还有跳转路径字符串。这样我们的配置文件就变成了如下代码所示：

<?xml version="1.0" encoding="UTF-8"?> 
<action-config> 
  <action path="/servlet/delUser" type="com.cjq.servlet.DelUserAction"> 
    <forward name="success">/del_success.jsp</forward> 
    <forward name="error">/del_error.jsp</forward> 
  </action> 
   
  <action path="/servlet/addUser" type="com.cjq.servlet.AddUserAction"> 
    <forward name="success">/add_success.jsp</forward> 
    <forward name="error">/add_error.jsp</forward> 
  </action> 
   
  <action path="/servlet/modifyUser" type="com.cjq.servlet.ModifyUserAction"> 
    <forward name="success">/modify_success.jsp</forward> 
    <forward name="error">/modify_error.jsp</forward> 
  </action> 
   
  <action path="/servlet/queryUser" type="com.cjq.servlet.QueryUserAction"> 
    <forward name="success">/query_success.jsp</forward> 
    <forward name="error">/query_error.jsp</forward> 
  </action> 
   
</action-config>

我们有了配置文件之后就要想法通过相关类读取，并且实现相应的功能。所以这里用dom4j来读取完成。其实如果能把这个逻辑捋顺之后就能发现，其实懂我们利用dom4j读取完配置文件的时候，我们是取得的是一个配套的匹配路径字符串、相应业务逻辑类还有处理业务逻辑之后跳转页面路径字符串。这样我们就能直截了当的去掉了if-else。（这里可能逻辑上会出现一些困难，但是看到下面的重构之后的testservlet中的代码和读取配置文件之后的代码就会一目了然）。

现在等待解决的问题就是我们要把从配置文件取得的一整套内容放到那里，当然这是毋庸置疑的要放到类中。所以我们就建立一个ActionMapping类来放我们的那一整套内容。

ActionMapping中的代码如下：

package com.bjpowernode.servlet; 
 
import java.util.Map; 
 
public class ActionMapping { 
 
  private String path; 
   
  private Object type; 
   
  private Map forwardMap; 
 
  public String getPath() { 
    return path; 
  } 
 
  public void setPath(String path) { 
    this.path = path; 
  } 
 
  public Object getType() { 
    return type; 
  } 
 
  public void setType(Object type) { 
    this.type = type; 
  } 
 
  public Map getForwardMap() { 
    return forwardMap; 
  } 
 
  public void setForwardMap(Map forwardMap) { 
    this.forwardMap = forwardMap; 
  } 
   
}

现在ActionMapping类已经有了，剩下的工作就是要利用dom4j来读取配置文件类，具体代码如下：

package com.bjpowernode.servlet; 
 
import java.io.InputStream; 
import java.util.HashMap; 
import java.util.Iterator; 
import java.util.Map; 
 
import org.dom4j.Document; 
import org.dom4j.DocumentException; 
import org.dom4j.Element; 
import org.dom4j.io.SAXReader; 
 
public class XmlConfigReader { 
 
   
  private static XmlConfigReader instance=new XmlConfigReader(); 
   
  ActionMapping actionMapping=new ActionMapping(); 
   
  private Document doc; 
   
  private Map actionMap=new HashMap(); 
   
  private XmlConfigReader(){ 
    try { 
      SAXReader reader=new SAXReader(); 
       
      InputStream in=Thread.currentThread().getContextClassLoader().getResourceAsStream("action_config.xml"); 
       
      doc=reader.read(in); 
       
    } catch (DocumentException e) { 
      // TODO Auto-generated catch block 
      e.printStackTrace(); 
    } 
     
     
  } 
   
   
   
   
  public ActionMapping getActionMapping(String path){ 
    synchronized(this){ 
       
      Object type=null; 
      /*if(action.containsKey(path)){ 
        type=action.get(path); 
      }*/ 
       
       
      Element eltAction = (Element)doc.selectObject("//action[@path=\"" + path + "\"]"); 
      try{ 
        type=Class.forName(eltAction.attributeValue("type")).newInstance(); 
      }catch(Exception e){ 
        e.printStackTrace(); 
      } 
       
       Element eltForwards = eltAction.element("forward"); 
         
        for (Iterator iter = eltForwards.elementIterator(); iter.hasNext();) { 
          Element eltForward = (Element) iter.next(); 
          actionMap.put( eltForward.attributeValue("name"),eltForward.getTextTrim());  
        }  
       
      actionMapping.setPath(path); 
      actionMapping.setType(type); 
      actionMapping.setForwardMap(actionMap); 
       
      return actionMapping; 
    } 
  } 
   
  public static synchronized XmlConfigReader getInstance(){ 
     
    return instance; 
  } 
   
   
  /** 
   * @param args 
   */ 
  public static void main(String[] args) { 
    // TODO Auto-generated method stub 
    ActionMapping actionMapping=XmlConfigReader.getInstance().getActionMapping("/servlet/delUser"); 
    System.out.println(actionMapping.getPath()); 
    System.out.println(actionMapping.getType()); 
    System.out.println(actionMapping.getForwardMap().toString()); 
  } 
 
}

我们通过返回ActionMapping来动态创建出action相应的实现类，进而完成业务逻辑和页面跳转，重构之后的TestServlet代码如下：

package com.bjpowernode.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 { 
 
   
  protected void doGet(HttpServletRequest request, HttpServletResponse response) 
      throws ServletException, IOException { 
     
    String requestURI=request.getRequestURI(); 
    System.out.println("request="+requestURI); 
    String path=requestURI.substring(requestURI.indexOf("/",1),requestURI.indexOf(".")); 
    System.out.println("path="+path); 
     
 
    String forward=""; 
    ActionMapping actionMapping=XmlConfigReader.getInstance().getActionMapping(path); 
    Action action=(Action)actionMapping.getType(); 
    try { 
      forward=action.execute(request, response); 
    } catch (Exception e) { 
      // TODO Auto-generated catch block 
      e.printStackTrace(); 
    } 
    request.getRequestDispatcher(forward).forward(request, response); 
  } 
 
   
  protected void doPost(HttpServletRequest request, HttpServletResponse response) 
      throws ServletException, IOException { 
    doGet(request,response); 
  } 
 
}

我们可以清晰的看到if-else已经没有了，字符串也已经没有了。通过这篇文章对if-else还有字符串问题的解决，又一次重构了testservlet代码，程序相对灵活许多。通过这一次的重构，我们已经看到了struts框架的雏形，

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