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Struts源码分析1：org.apache.struts.action.Action

by sundy 8/7/2009 11:53:32 AM

前言：发现很多j2ee的程序员基础都差得不行，会用ssh的甚至都不知道为何要这样，以及如何设计的。因此为大家简单的剖析一下Struts的设计，以资借鉴。

actoin中的方法大多是针对 Messages，Errors，token的一些操作。

package org.apache.struts.action;
import org.apache.struts.Globals;
import org.apache.struts.config.ModuleConfig;
import org.apache.struts.util.MessageResources;
import org.apache.struts.util.ModuleUtils;
import org.apache.struts.util.RequestUtils;
import org.apache.struts.util.TokenProcessor;
import javax.servlet.ServletContext;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;
import java.util.Locale;
/**
* Action必须以线程安全的方式编写，
* 因为controller会为同时存在的多个request共享一个实例。
* 所以编写时要注意：
*
* 实例和static变量不能存储与具体request相关的信息。
*
* 存取受保护的JavaBeans, session 变量等资源时，必须使用同步（synchronized）。
*
*
* 当一个Action实例被第一次创建时，controller会用一个非空参数
*（标识这个servlet实例和附属他的Action）调用 setServlet 。
* 当实例被关闭时，setServlet会被再次调用，用一个null
* 参数来清空这个Action的信息
*
*/
public class Action {
/**
 * org.apache.struts.util.TokenProcessor类：令牌产生器，用于防止事务重复提交
*/
private static TokenProcessor token = TokenProcessor.getInstance();
// NOTE: We can make the token variable protected and remove Action's
// token methods or leave it private and allow the token methods to
// delegate(委托) their calls.
// ----------------------------------------------------- Instance Variables
/**
 * Action附属的servlet。
*/
protected transient ActionServlet servlet = null;
// ------------------------------------------------------------- Properties
public ActionServlet getServlet() {
return (this.servlet);
 }
/**
 * 设置Action附属的servlet，或释放所有资源（servlet=null）
 * @param servlet The new controller servlet, if any
*/
public void setServlet(ActionServlet servlet) {
this.servlet = servlet;
// :FIXME: Is this suppose to release resources?
 }
// --------------------------------------------------------- Public Methods
/**
 * 非HTTP的execute方法，一般不用。
 * /
 public ActionForward execute(ActionMapping mapping, ActionForm form,
 ServletRequest request, ServletResponse response)
 throws Exception {
 try {
 return execute(mapping, form, (HttpServletRequest) request,
 (HttpServletResponse) response);
 } catch (ClassCastException e) {
 return null;
 }
 }
 /**
 * 处理 HTTP request, 创建相应的(corresponding)
 * HTTP response (或定向到其他创建response 的组件
 * ), 返回 { ActionForward} 实例来通知control如何跳转。
 * 或当处理完成时返回null
 * 注：当请求发送到Action时就会自动执行这个execute方法，所以一般简单的Action就重写这个方法即可//by wzl.
 * @param mapping The ActionMapping used to select this instance （用来选择这个实例？？）
 * @param form 可选的 ActionForm bean
 * @param request The HTTP request
 * @param response The HTTP response
 * @return forward 通知 control 应该跳转的页面, 或null (当业务完成时)
 * @throws Exception if the application business logic throws an
 * exception
 * @since Struts 1.1
*/
public ActionForward execute(ActionMapping mapping, ActionForm form,
 HttpServletRequest request, HttpServletResponse response)
throws Exception {
return null;
 }
// ---------------------------------------------------- Protected Methods
/**
 * 为request添加 messages
 * 在JSP用用 < html:messages> 标签使用 (if messages="true" is set),
 * 参数message 必须被初始化 //org.apache.struts.action.ActionMessages
 * Otherwise, ensure that the request attribute is not set.？？？
 *
 * @param request 被添加message的request请求
 * @param messages ActionMessages 需要添加的message
 * @since Struts 1.2.1
*/
protected void addMessages(HttpServletRequest request,
 ActionMessages messages) {
if (messages == null) {
// bad programmer! *slap*
return;
 }
// 取得request中的requestMessages, 没有就创建一个
 ActionMessages requestMessages =
 (ActionMessages) request.getAttribute(Globals.MESSAGE_KEY); //"org.apache.struts.action.ACTION_MESSAGE";
if (requestMessages == null) {
 requestMessages = new ActionMessages();
 }
// messages加入到requestMessages
 requestMessages.add(messages);
// if still empty, just wipe it out from the request
if (requestMessages.isEmpty()) {
 request.removeAttribute(Globals.MESSAGE_KEY);
return;
 }
// Save the messages
 request.setAttribute(Globals.MESSAGE_KEY, requestMessages);
 }
/**
 * Adds the specified errors keys into the appropriate request attribute
 * for use by the <html:errors> tag, if any messages are required.
 * Initialize the attribute if it has not already been. Otherwise, ensure
 * that the request attribute is not set.
 * 注：基本与addMessages相同，只是这里的ActionMessages含的是错误信息，在页面用 <html:errors>使用。/by wzl
 * @param request The servlet request we are processing
 * @param errors Errors object
 * @since Struts 1.2.1
*/
protected void addErrors(HttpServletRequest request, ActionMessages errors) {
if (errors == null) {
// bad programmer! *slap*
return;
 }
// get any existing errors from the request, or make a new one
 ActionMessages requestErrors =
 (ActionMessages) request.getAttribute(Globals.ERROR_KEY);
if (requestErrors == null) {
 requestErrors = new ActionMessages();
 }
// add incoming errors
 requestErrors.add(errors);
// if still empty, just wipe it out from the request
if (requestErrors.isEmpty()) {
 request.removeAttribute(Globals.ERROR_KEY);
return;
 }
// Save the errors
 request.setAttribute(Globals.ERROR_KEY, requestErrors);
 }
/**
 * Generate a new transaction token, to be used for enforcing a single
 * request for a particular transaction.
 * 为需要处理特殊事务的request生成一个事务token
 * @param request The request we are processing
 * @return The new transaction token.
*/
protected String generateToken(HttpServletRequest request) {
return token.generateToken(request);
 }
/**
 * Retrieves any existing errors placed in the request by previous
 * actions. This method could be called instead of creating a <code>new
 * ActionMessages()</code> at the beginning of an <code>Action</code>.
 * This will prevent saveErrors() from wiping out any existing Errors
 *
 * 获得被上一个Action设置的error信息，这个方法可用来
 *初始化一个ActionMessages。可以用来防止saveErrors()清空已存在的Errors。
 *
 * @param request The servlet request we are processing
 * @return the Errors that already exist in the request, or a new
 * ActionMessages object if empty.
 * @since Struts 1.2.1
*/
protected ActionMessages getErrors(HttpServletRequest request) {
 ActionMessages errors =
 (ActionMessages) request.getAttribute(Globals.ERROR_KEY);
if (errors == null) {
 errors = new ActionMessages();
 }
return errors;
 }
/**
 * 返回用户当前选择的 Locale。 //java.util.Locale 对象表示了特定的地理、政治和文化地区。
 *
 * @param request The request we are processing
 * @return The user's currently selected Locale.
*/
protected Locale getLocale(HttpServletRequest request) {
return RequestUtils.getUserLocale(request, null);
 }
/**
 * 大体同getError(request)
 * Retrieves any existing messages placed in the request by previous
 * actions. This method could be called instead of creating a <code>new
 * ActionMessages()</code> at the beginning of an <code>Action</code> This
 * will prevent saveMessages() from wiping out any existing Messages 
 *
 * @param request The servlet request we are processing
 * @return the Messages that already exist in the request, or a new
 * ActionMessages object if empty.
 * @since Struts 1.2.1
*/
protected ActionMessages getMessages(HttpServletRequest request) {
 ActionMessages messages =
 (ActionMessages) request.getAttribute(Globals.MESSAGE_KEY);
if (messages == null) {
 messages = new ActionMessages();
 }
return messages;
 }
/**
 * 为当前模型返回默认的MessageResources ？？ //org.apache.struts.util.MessageResources
 *
 * @param request The servlet request we are processing
 * @return The default message resources for the current module.
 * @since Struts 1.1
*/
protected MessageResources getResources(HttpServletRequest request) {
return ((MessageResources) request.getAttribute(Globals.MESSAGES_KEY));
 }
/**
 * Return the specified message resources for the current module.
 * 根据key为当前module返回特定的MessageResources
 * 看不懂
 * @param request The servlet request we are processing
 * @param key The key specified in the message-resources element for
 * the requested bundle.
 * @return The specified message resource for the current module.
 * @since Struts 1.1
*/
protected MessageResources getResources(HttpServletRequest request,
 String key) {
// Identify the current module
 ServletContext context = getServlet().getServletContext();
 ModuleConfig moduleConfig =
 ModuleUtils.getInstance().getModuleConfig(request, context);
// Return the requested message resources instance
return (MessageResources) context.getAttribute(key
+ moduleConfig.getPrefix());
 }
/**
 * Returns <code>true</code> if the current form's cancel button was
 * pressed. This method will check if the <code>Globals.CANCEL_KEY</code>
 * request attribute has been set, which normally occurs if the cancel
 * button generated by CancelTag was pressed by the user
 * in the current request. If <code>true</code>, validation performed by
 * an ActionForm's <code>validate()</code> method will
 * have been skipped by the controller servlet.
 *
 * 当form的cancel按键？被按下时返回true。该方法会检查 request的
 * Globals.CANCEL_KEY属性。若为true，ActionForm中的validate()将被跳过。
 *
 * Since Action 1.3.0, the mapping for a cancellable Action must also have
 * the new "cancellable" property set to true. If "cancellable" is not set, and
 * the magic Cancel token is found in the request, the standard Composable
 * Request Processor will throw an InvalidCancelException. 
 *
 * @param request The servlet request we are processing
 * @return <code>true</code> if the cancel button was pressed;
 * <code>false</code> otherwise.
*/
protected boolean isCancelled(HttpServletRequest request) {
return (request.getAttribute(Globals.CANCEL_KEY) != null);
 }
/**
 * 在当前session中存有事务token时返回true。当存在以下情况时返回false：
 * <ul>
 *
 * request中无session
 *
 * session中无事务token
 * <li>No transaction token included as a request parameter</li>
 * request中没有事务token属性。
 *
 * 存在是事务token属性与session中的不匹配。
 * </ul>
 *
 * @param request The servlet request we are processing
 * @return <code>true</code> if there is a transaction token and it is
 * valid; <code>false</code> otherwise.
*/
protected boolean isTokenValid(HttpServletRequest request) {
return token.isTokenValid(request, false);
 }
/**
 * Return <code>true</code> if there is a transaction token stored in
 * the user's current session, and the value submitted as a request
 * parameter with this action matches it. Returns <code>false</code> under
 * any of the following circumstances:
 * 重写上一个方法，添加参数 reset 决定是否在确认后重置token
 * <ul>
 *
 * <li>No session associated with this request</li> <li>No transaction
 * token saved in the session</li>
 *
 * <li>No transaction token included as a request parameter</li>
 *
 * <li>The included transaction token value does not match the transaction
 * token in the user's session</li>
 *
 * </ul>
 *
 * @param request The servlet request we are processing
 * @param reset Should we reset the token after checking it?
 * @return <code>true</code> if there is a transaction token and it is
 * valid; <code>false</code> otherwise.
*/
protected boolean isTokenValid(HttpServletRequest request, boolean reset) {
return token.isTokenValid(request, reset);
 }
/**
 * Reset the saved transaction token in the user's session. This
 * indicates that transactional token checking will not be needed on the
 * next request that is submitted.
 * 重置token
 * @param request The servlet request we are processing
*/
protected void resetToken(HttpServletRequest request) {
 token.resetToken(request);
 }
/**
 * Save the specified error messages keys into the appropriate request
 * attribute for use by the <html:errors> tag, if any messages are
 * required. Otherwise, ensure that the request attribute is not
 * created.
 * 重置并设置Errors。
 * @param request The servlet request we are processing
 * @param errors Error messages object
 * @since Struts 1.2
*/
protected void saveErrors(HttpServletRequest request, ActionMessages errors) {
// Remove any error messages attribute if none are required
if ((errors == null) || errors.isEmpty()) {
 request.removeAttribute(Globals.ERROR_KEY);
return;
 }
// Save the error messages we need
 request.setAttribute(Globals.ERROR_KEY, errors);
 }
/**
 * Save the specified messages keys into the appropriate request
 * attribute for use by the <html:messages> tag (if messages="true"
 * is set), if any messages are required. Otherwise, ensure that the
 * request attribute is not created.
 * 重置并设置request中的Messages
 * @param request The servlet request we are processing.
 * @param messages The messages to save. <code>null</code> or empty
 * messages removes any existing ActionMessages in the
 * request.
 * @since Struts 1.1
*/
protected void saveMessages(HttpServletRequest request,
 ActionMessages messages) {
// Remove any messages attribute if none are required
if ((messages == null) || messages.isEmpty()) {
 request.removeAttribute(Globals.MESSAGE_KEY);
return;
 }
// Save the messages we need
 request.setAttribute(Globals.MESSAGE_KEY, messages);
 }
/**
 * Save the specified messages keys into the appropriate session
 * attribute for use by the <html:messages> tag (if messages="true"
 * is set), if any messages are required. Otherwise, ensure that the
 * session attribute is not created.
 * 重置并设置session中的Messages
 * @param session The session to save the messages in.
 * @param messages The messages to save. <code>null</code> or empty
 * messages removes any existing ActionMessages in the
 * session.
 * @since Struts 1.2
*/
protected void saveMessages(HttpSession session, ActionMessages messages) {
// Remove any messages attribute if none are required
if ((messages == null) || messages.isEmpty()) {
 session.removeAttribute(Globals.MESSAGE_KEY);
return;
 }
// Save the messages we need
 session.setAttribute(Globals.MESSAGE_KEY, messages);
 }
/**
 * Save the specified error messages keys into the appropriate session
 * attribute for use by the <html:messages> tag (if
 * messages="false") or <html:errors>, if any error messages are
 * required. Otherwise, ensure that the session attribute is empty.
 * 重置并设置session中的Errors
 * @param session The session to save the error messages in.
 * @param errors The error messages to save. <code>null</code> or empty
 * messages removes any existing error ActionMessages in
 * the session.
 * @since Struts 1.3
*/
protected void saveErrors(HttpSession session, ActionMessages errors) {
// Remove the error attribute if none are required
if ((errors == null) || errors.isEmpty()) {
 session.removeAttribute(Globals.ERROR_KEY);
return;
 }
// Save the errors we need
 session.setAttribute(Globals.ERROR_KEY, errors);
 }
/**
 * Save a new transaction token in the user's current session, creating
 * a new session if necessary.
 *
 * @param request The servlet request we are processing
*/
protected void saveToken(HttpServletRequest request) {
 token.saveToken(request);
 }
/**
 * Set the user's currently selected <code>Locale</code> into their
 * <code>HttpSession</code>.
 *
 * @param request The request we are processing
 * @param locale The user's selected Locale to be set, or null to select
 * the server's default Locale
*/
protected void setLocale(HttpServletRequest request, Locale locale) {
 HttpSession session = request.getSession();
if (locale == null) {
 locale = Locale.getDefault();
 }
 session.setAttribute(Globals.LOCALE_KEY, locale);
 }
}