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Struts开发指南之工作流程

 2008-01-05 19:37:51 来源:WEB开发网   
核心提示:下图是Struts的工作流程,前边我们提到,Struts开发指南之工作流程,所有的请求都提交给ActionServlet来处理,点击查看大图ActionServlet是一个FrontController,并且采用validator插件进行form的验证,但是代码树立了一个不好的榜样,它是一个标准的Servlet,它将r

  下图是Struts的工作流程,前边我们提到,所有的请求都提交给ActionServlet来处理。

Struts开发指南之工作流程
点击查看大图


  ActionServlet是一个FrontController,它是一个标准的Servlet,它将request转发给RequestPRocessor来处理,

  ActionMapping是ActionConfig的子类,实质上是对struts-config.xml的一个映射,从中可以取得所有的配置信息

  RequestProcessor根据提交过来的url,如*.do,从ActionMapping 中得到相应的ActionForn和Action。然后将request的参数对应到ActionForm中,进行form验证。假如验证通过则调用Action的execute()方法来执行Action,最终返回ActionFoward。

  ActionFoward是对mapping中一个foward的包装,对应于一个url

  ActionForm使用了ViewHelper模式,是对Html中form的一个封装。其中包含有validate方法,用于验证form数据的有效性。ActionForm是一个符合javaBean规范的类,所有的属性都应满足get和set对应。对于一些复杂的系统,还可以采用DynaActionForm来构造动态的Form,即通过预制参数来生成Form。这样可以更灵活的扩展程序。

  ActionErrors是对错误信息的包装,一旦在执行action或者form.validate中出现异常,即可产生一个ActionError并最终加入到ActionErrors。在Form验证的过程中,假如有Error发生,则会将页面重新导向至输入页,并提示错误。

  Action是用于执行业务逻辑的RequsestHandler。每个Action都只建立一个instance。Action不是线程安全的,所以不应该在Action中访问特定资源。一般来说,应改使用 Business Delegate 模式来对Business tier进行访问以解除耦合。

  Struts提供了多种Action供选择使用。普通的Action只能通过调用execute执行一项任务,而DispatchAction可以根据配置参数执行,而不是仅进入execute()函数,这样可以执行多种任务。如insert,update等。LookupDispatchAction可以根据提交表单按钮的名称来执行函数。

  我们可以先回到刚才的例子,理解一下Struts的流程。

  下面我们看Struts自带的example实例:

  说明:实例二是Struts自带的example程序, 实现了登录,注册,修改功能。

  代码中大量应用了struts taglib,并且采用validator插件进行form的验证。

  但是代码树立了一个不好的榜样,即把大量的业务逻辑写在了action中。

  部分代码如下:

  登录:logon.jsp

<%@ page contentType="text/html;charset=UTF-8" language="java" %>

// 声明Taglib
<%@ taglib uri="/WEB-INF/struts-bean.tld" prefix="bean" %>
<%@ taglib uri="/WEB-INF/struts-html.tld" prefix="html" %>

<html:html locale="true">
<head>
 // bean是用来从applicationResource中读取i18n信息
 <title><bean:message key="logon.title"/></title>
 <html:base/>
</head>
<body bgcolor="white">

// 错误信息部分
<html:errors/>

// 登录form,action为logion.do
<html:form action="/logon" focus="username"

<table border="0" width="100%">

 <tr>
  <th align="right">
   <bean:message key="prompt.username"/>:
  </th>
  <td align="left">
   <html:text property="username" size="16" maxlength="18"/>
  </td>
 </tr>

 <tr>
  <th align="right">
   <bean:message key="prompt.passWord" bundle="alternate"/>:
  </th>
  <td align="left">
   <html:password property="password" size="16" maxlength="18" redisplay="false"/>
  </td>
 </tr>

 <tr>
  <td align="right">
   <html:submit value="Submit"/>
  </td>
  <td align="left">
   <html:reset/>
  </td>
 </tr>

</table>

</html:form>

// Validator插件,用于form验证
<html:javascript formName="logonForm" dynamicJavascript="true" staticJavascript="false"/>
<script language="Javascript1.1" src="staticJavascript.jsp"></script>

</body>
</html:html>
  struts-config.xml配置

<form-beans>

<!-- Logon form bean -->
 <form-bean name="logonForm" type="org.apache.struts.validator.DynaValidatorForm">
  <form-property name="username" type="java.lang.String"/>
  <form-property name="password" type="java.lang.String"/>
 </form-bean>

 <!-- Subscription form bean -->
 <form-bean name="subscriptionForm"type="org.apache.struts.webapp.example.SubscriptionForm"/>

 </form-beans>
 <action-mappings>

 <!-- Edit mail subscription -->
 <action path="/editSubscription"
type="org.apache.struts.webapp.example.EditSubscriptionAction"
attribute="subscriptionForm"
scope="request"
validate="false">
  <forward name="failure" path="/mainMenu.jsp"/>
  <forward name="sUCcess" path="/subscription.jsp"/>
 </action>
...
  subscriptionForm 是一个标准的ActionForm,其中reset方法用于清除form的值,validate方法用于验证

public final class SubscriptionForm extends ActionForm {
// The maintenance action we are performing (Create or Edit).
private String action = "Create";
// Should we auto-connect at startup time?
private boolean autoConnect = false;
// The host name.
private String host = null;
private String password = null;
private String type = null;
private String username = null;

public String getAction() { return (this.action); }
public void setAction(String action) { this.action = action; }

public boolean getAutoConnect() { return (this.autoConnect); }
public void setAutoConnect(boolean autoConnect) { this.autoConnect = autoConnect; }

public String getHost() { return (this.host); }
public void setHost(String host) { this.host = host; }

public String getPassword() { return (this.password); }
public void setPassword(String password) { this.password = password; }

public String getType() { return (this.type); }
public void setType(String type) { this.type = type; }

public String getUsername() { return (this.username); }
public void setUsername(String username) { this.username = username; }

/**
* Reset all properties to their default values.
*
* @param mapping The mapping used to select this instance
* @param request The servlet request we are processing
*/
public void reset(ActionMapping mapping, HttpServletRequest request) {

 this.action = "Create";
 this.autoConnect = false;
 this.host = null;
 this.password = null;
 this.type = null;
 this.username = null;

}


/**
* Validate the properties that have been set from this HTTP request,
* and return an <code>ActionErrors</code> object that encapsulates any
* validation errors that have been found. If no errors are found, return
* <code>null</code> or an <code>ActionErrors</code> object with no
* recorded error messages.
*
* @param mapping The mapping used to select this instance
* @param request The servlet request we are processing
*/
public ActionErrors validate(ActionMapping mapping,
HttpServletRequest request) {

 ActionErrors errors = new ActionErrors();

 if ((host == null) (host.length() < 1))
  errors.add("host",
  new ActionError("error.host.required"));
 if ((username == null) (username.length() < 1))
  errors.add("username",
  new ActionError("error.username.required"));
 if ((password == null) (password.length() < 1))
  errors.add("password",
  new ActionError("error.password.required"));
 if ((type == null) (type.length() < 1))
  errors.add("type",
  new ActionError("error.type.required"));
 else if (!"imap".equals(type) && !"pop3".equals(type))
  errors.add("type",new ActionError("error.type.invalid", type));
 return (errors);
 }
}

  logonAction

public final class LogonAction extends Action {
/**
* Process the specified HTTP request, and create the corresponding HTTP
* response (or forward to another web component that will create it).
* Return an <code>ActionForward</code> instance describing where and how
* control should be forwarded, or <code>null</code> if the response has
* already been completed.
*
* @param mapping The ActionMapping used to select this instance
* @param form The optional ActionForm bean for this request (if any)
* @param request The HTTP request we are processing
* @param response The HTTP response we are creating
*
* @exception Exception if business logic throws an exception
*/
public ActionForward execute(ActionMapping mapping,
ActionForm form,
HttpServletRequest request,
HttpServletResponse response)
throws Exception {

 // Extract attributes we will need
 Locale locale = getLocale(request);
 MessageResources messages = getResources(request);
 User user = null;

 // Validate the request parameters specified by the user
 ActionErrors errors = new ActionErrors();
 String username = (String)
 PropertyUtils.getSimpleProperty(form, "username");
 String password = (String)
 PropertyUtils.getSimpleProperty(form, "password");
 UserDatabase database = (UserDatabase)
 servlet.getServletContext().getAttribute(Constants.DATABASE_KEY);
 if (database == null)
  errors.add(ActionErrors.GLOBAL_ERROR,
  new ActionError("error.database.missing"));
 else {
  user = getUser(database, username);
  if ((user != null) && !user.getPassword().equals(password))
   user = null;
  if (user == null)
   errors.add(ActionErrors.GLOBAL_ERROR,
   new ActionError("error.password.mismatch"));
 }

// Report any errors we have discovered back to the original form
if (!errors.isEmpty()) {
 saveErrors(request, errors);
 return (mapping.getInputForward());
}

// Save our logged-in user in the session
HttpSession session = request.getSession();
session.setAttribute(Constants.USER_KEY, user);
if (log.isDebugEnabled()) {
 log.debug("LogonAction: User '" + user.getUsername() +
"' logged on in session " + session.getId());
}

// Remove the obsolete form bean
if (mapping.getAttribute() != null) {
 if ("request".equals(mapping.getScope()))
  request.removeAttribute(mapping.getAttribute());
 else
  session.removeAttribute(mapping.getAttribute());
}

// Forward control to the specified success URI
return (mapping.findForward("success"));

}

/**
* Look up the user, throwing an exception to simulate business logic
* rule exceptions.
*
* @param database Database in which to look up the user
* @param username Username specified on the logon form
*
* @exception ModuleException if a business logic rule is violated
*/
public User getUser(UserDatabase database, String username)
throws ModuleException {

// Force an ArithmeticException which can be handled eXPlicitly
if ("arithmetic".equals(username)) {
 throw new ArithmeticException();
}

// Force an application-specific exception which can be handled
if ("expired".equals(username)) {
 throw new ExpiredPasswordException(username);
}

// Look up and return the specified user
return ((User) database.findUser(username));

}
}

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