【斗医】【5】Web应用开发20天

三、页面跳转封装

【接上】在《【斗医】【4】Web应用开发50天》中页面跳转封装只做了如下工作：名称为action的Servlet启动时，解析/WEB-INF/config下各业务模块的XXX-action.xml，并把其业务封装为FrameBusiness对象缓存到全局变量Map中：

接下来要完成如下功能：

Web容器(Tomcat)接受到HTTP请求后，Web容器把HTTP转换为HttpServletRequest对象，然后根据请求名称匹配规则找到相应的Servlet，调用servlet-class对应类的doGet()或doPost()方法，在该方法中根据请求名称从全局缓存(FrameCache.businessMap)中读取业务对象（FrameBusiness），由FrameBusiness对象跳转到相应的页面。

1、配置名称为action的Servlet。

打开D:\medical\war\WEB-INF\web.xml文件，在里面填充如下内容：

    
        action
        com.medical.frame.FrameLauncher
        1
    
    
        action
        *.act
    
    
         index.html
    

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【备注】：该内容在前面已配置过，这里再强调一次一方面是理顺思路，另一方面是强调Web容器处理HTTP请求的流程。

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2、把HttpServletRequest请求均交给get处理

打开D:\medical\src\com\medical\frame\FrameLauncher.java，把doPost()处理交给doGet()：

@Override
public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException
{
    doGet(request, response);
}

3、为了保持FrameLauncher功能的简洁性，这里定义一个FrameDispatcher类，FrameLauncher.doGet()的业务逻辑交给FrameDispatcher处理：

I、定义com.medical.frame.FrameDispatcher.java类

public class FrameDispatcher
{
    private HttpServlet servlet = null;
    /**
     * 构造器
     */
    public FrameDispatcher(HttpServlet servlet)
    {
        this.servlet = servlet;
    }
    public void process(HttpServletRequest request, HttpServletResponse response) throws FrameException
    {
        // TODO
    }
}

II、FrameLauncher.doGet()交给FrameDispatcher对象处理

@Override
public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException
{
    FrameDispatcher dispatcher = new FrameDispatcher(this);
    try
    {
        dispatcher.process(request, response);
    }
    catch (FrameException e)
    {
        logger.error(e.getErrorDesc(), e);
    }
}

4、定义FrameDispatcher.getRequestName(HttpServletRequest)方法从HttpServletRequest对象中解析出请求名称（比如从/medical/index.act中获取index）

/**
 * 由HttpServletRequest对象获取请求名称
 */
private String getRequestName(HttpServletRequest request)
{
    String name = request.getRequestURI();
    if (name == null)
    {
        return null;
    }
    if (name.endsWith(FrameConstant.BUS_NAME_POSTFIX) == false)
    {
        return null;
    }
    int headIndex = name.lastIndexOf("/") + 1;
    int rearIndex = name.lastIndexOf(FrameConstant.BUS_NAME_POSTFIX);
    return name.substring(headIndex, rearIndex);
}

5、修改FrameDispatcher.process()方法，其功能是由业务名称获取对应的业务对象，然后由业务对象的forward来决定跳转页面

6、下面初步测试一下：

I、修改D:\medical\war\index.html文件，该文件加载完就跳转到index.act

    
        
        
            top.location="index.act";
        
      

II、修改D:\medical\war\WEB-INF\config\sm\system-action.xml文件

当系统加载时名称为action的Servlet会把该文件读入全局缓存。访问index.html时执行top.location="index.act"，action接受到"*.act"就执行FrameDispatcher.process()方法，从而跳转到/module/main/main.html页面

III、在D:\medical\war\module\main\下创建main.html文件，这里只是为了测试，所以main.html只是输出一个

This is main page!

标题：

    
              
    
    
        
This is main page!
    

IV、启动Tomcat服务，在浏览器中输入http://localhost:8080/medical，会发现页面直接把

This is main page!

显示出来了，见下图：

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【备注】：细心的读者可能发现了页面进入了main.html，但地址却依旧停留在index.act处，见上图。其中原因请大家在谷歌上搜索一下“JSP forward”，有文章会给出详细说明。

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7、再仔细考虑一个场景：在跳转到页面A之前，（1）有可能需要把当前页面的数据保存在数据库中，（2）或者需要进行一些逻辑判断，符合条件才能进入A页面，不符合则不能进入A页面。这就是当时XXX-action.xml中业务定义"business-class"的原因，但我们的FrameDispatcher.process()并没有这方面的处理，现在进行修改：

I、定义缺省跳转动作执行类com.medical.frame.FrameDefaultAction.java

/**
 * 斗医系统业务缺省跳转处理器
 *
 * @author qingkechina
 */
public class FrameDefaultAction
{
    /**
     * 请求对象
     */
    protected HttpServletRequest request = null;
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     
    /**
     * 响应对象
     */
    protected HttpServletResponse response = null;
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     
    /**
     * 会话对象
     */
    protected HttpSession session = null;
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     
    public void setRequest(HttpServletRequest request)
    {
        this.request = request;
    }
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     
    public void setResponse(HttpServletResponse response)
    {
        this.response = response;
    }
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     
    public void setSession(HttpSession session)
    {
        this.session = session;
    }
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     
    /**
     * 读取Request对象中的参数
     */
    public String getParameter(String param)
    {
        return request.getParameter(param);
    }
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     
    /**
     * 缺省响应动作
     */
    public String execute() throws FrameException
    {
        return null;
    }
}

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【备注】：这里没有使用接口或抽象类，建议读者在自已实现该功能时最好能抽象出接口，这样做的好处可参见设计模式相关内容

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II、定义动作工厂，可以根据XXX-action.xml中的业务business-class名称把相关的跳转动作类反射出来

package com.medical.frame;
import com.medical.frame.constant.FrameConstant;
import com.medical.frame.constant.FrameErrorCode;
/**
 * 斗医系统业务跳转动作工厂类
 *
 * @author qingkechina
 */
public class FrameActionFactory
{
    private static FrameActionFactory instance = new FrameActionFactory();
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          
    private FrameActionFactory()
    {
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                              
    }
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          
    public static FrameActionFactory getInstance()
    {
        return instance;
    }
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          
    /**
     * 反射跳转动作实现类
     */
    public FrameDefaultAction implement(String className) throws FrameException
    {
        if (className == null || className.trim().length() == 0)
        {
            className = FrameConstant.FORWARD_DEFAULT_ACTION;
        }
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                              
        try
        {
            return (FrameDefaultAction) Class.forName(className).newInstance();
        }
        catch (Exception e)
        {
            throw new FrameException(FrameErrorCode.JAVA_REFLECT_ERROR, e);
        }
    }
}

III、修改FrameDispatcher.process()方法，在其中增加跳转动作逻辑部分的处理（即下图红框部分）：

8、测试跳转功能：

I、打开D:\medical\war\WEB-INF\config\sm\system-action.xml文件，对"index.act"动作指定逻辑响应处理类Demo

II、定义com.medical.frame.forward.Demo类，该类继承FrameDefaultAction类，并重写execute()方法

package com.medical.frame.forward;
import com.medical.frame.FrameDefaultAction;
import com.medical.frame.FrameException;
public class Demo extends FrameDefaultAction
{
    @Override
    public String execute() throws FrameException
    {
        // 这里可以处理一些逻辑
        System.out.println("===================这里可以进行逻辑处理");
        // 逻辑处理完后跳转到相应页面
        return "login.act";
    }
}

从代码上可以看出，这里逻辑处理完之后，就直接跳转到login.act对应的页面

III、打开D:\medical\war\WEB-INF\config\sm\system-action.xml文件，修改"login.act"对应的业务配置

IV、在D:\medical\war\module\login下创建login.html文件，填充如下内容：

    
        
    
    
        
This is Login page!
    

V、启动Tomcat后在浏览器中输入http://localhost:8080/medical回车，查看页面，页面上输出“This is Login page!”，这说明页面是跳转到了login.html上，如图：

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【备注】：上面的测试也说明当业务配置了business-class，则相应动作执行类跳转动作的优先级要高于

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OK，到这里跳转封装的基本功能已完成，可能会有人问：“只是一个跳转，使用HTML的标签，岂不是更简单，何苦折腾这么一通呢？”

有这个疑问是一件好事情，说明大家都进行了思考。正如上面所说，一些逻辑性处理需要在服务端进行（如有些场景需要根据逻辑判断决定跳转到哪个页面，若纯使用WEB前端处理，显的客户端比较胖或者叫富客户端），另外把眼光放远一些，试想Struts做了哪些事情呢？除了过滤器之外无非也是逻辑判断，数据加工后的页面显示。

下面我们再理顺一下思路：

（1）启动Tomcat时，会加载web.xml，根据web.xml把名称为action的Servlet拉起

（2）名称为action的Servlet启动时，根据其配置规则反射FrameLauncher类，并调用它的init()方法

（3）在init()方法中会读取运行环境中的XXX-action.xml文件，解析该文件后把动作名及动作名对应的业务对象FrameBusiness缓存入全局变量

（4）当在浏览器中输入http://localhost:8080/medical时，Tomcat根据web.xml配置首先加载index.html

（5）在index.html加载完毕后直接使用top.location="index.act"跳转到index.act

（6）tomcat服务器一看到是.act结尾的请求，就使用FrameLauncher的doGet()方法来处理

（7）FrameLauncher.doGet()委托给FrameDispatcher.process()，在process()中它根据index.act在全局缓存中查找FrameBusiness

（8）首先看一下FrameBusiness是否有class-name，若有就获取逻辑处理类指定的路径；若没有就使用forward指定的路径

（9)然后把该路径交给HttpServlet进行具体的页面跳转