📄 csdn_struts原理与应用（三）.htm
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<P><STRONG>ActionErrors</STRONG>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，如果有Error发生，则会将页面重新导向至输入页，并提示错误。
<P><STRONG>Action</STRONG>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。
<P>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。
<P>我们可以先回到刚才的例子，理解一下Struts的流程。
<P>下面我们看Struts自带的example实例： </P><FONT size=+2>
<H1>Chapter 6: Example 2: Login Application </H1>
<P><FONT color=blue>Struts principle and practice </FONT></P>
<P>说明：实例二是Struts自带的example程序, 实现了登录，注册，修改功能 </P>
<P>代码中大量应用了struts taglib，并且采用validator插件进行form的验证
<P>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。
<P>部分代码如下：
<P>登录：logon.jsp
<P>
<TABLE>
<TBODY>
<TR>
<TD class=code>
<P> </P></TD></TR></TBODY></TABLE><TEXTAREA class=code style="WIDTH: 473px; HEIGHT: 112px" name=textarea rows=5 cols=51> <%@ 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>
</TEXTAREA>
<P>
<P><STRONG>struts-config.xml配置</STRONG></P>
<P><TEXTAREA class=code style="WIDTH: 473px; HEIGHT: 112px" name=textarea rows=5 cols=51> <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>
...
</TEXTAREA> </P>
<P><BR><STRONG>subscriptionForm</STRONG>
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
<P><TEXTAREA class=code style="WIDTH: 469px; HEIGHT: 105px" name=textarea rows=5 cols=51>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);
}
}
</TEXTAREA>
<P><STRONG>logonAction</STRONG>
<P><TEXTAREA class=code style="WIDTH: 471px; HEIGHT: 70px" name=textarea2 rows=3 cols=51>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"));
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