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Struts开发指南之工作流程

王朝other·作者佚名  2008-05-31
窄屏简体版  字體: |||超大  

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。

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"

onsubmit="return validateLogonForm(this);">

<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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