java中怎样获取类的context，java中action请求是什么

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在Struts2开发中,除了将请求参数自动设置到Action的字段中,我们往往也需要在Action里直接获取请求(Request)或会话(Session)的一些信息,甚至需要直接对JavaServlet Http的请求(HttpServletRequest),响应(HttpServletResponse)操作.我们需要在Action中取得request请求参数"username"的值:

ActionContext context= ActionContext.getContext();

Map params= context.getParameters();

String username=(String) params.get("username");

on执行时的上下文,上下文可以看作是一个容器(其实我们这里的容器就是一个Map而已),它存放的是Action在执行时需要用到的对象.一般情况,我们的ActionContext都是通过: ActionContext context=(ActionContext) actionContext.get();来获取的.我们再来看看这里的actionContext对象的创建:

static ThreadLocal actionContext= new ActionContextThreadLocal();

ActionContextThreadLocal是实现ThreadLocal的一个内部类.ThreadLocal可以命名为"线程局部变量",它为每一个使用该变量的线程都提供一个变量值的副本,使每一个线程都可以独立地改变自己的副本,而不会和其它线程的副本冲突.这样,我们ActionContext里的属性只会在对应的当前请求线程中可见,从而保证它是线程安全的.

通过ActionContext取得HttpSession: Map session= ActionContext.getContext().getSession();

ServletActionContext(com.opensymphony.webwork. ServletActionContext),这个类直接继承了我们上面介绍的ActionContext,它提供了直接与Servlet相关对象访问的功能,它可以取得的对象有:

(1)javax.servlet.http.HttpServletRequest: HTTPservlet请求对象

(2)javax.servlet.http.HttpServletResponse: HTTPservlet相应对象

(3)javax.servlet.ServletContext: Servlet上下文信息

(4)javax.servlet.ServletConfig: Servlet配置对象

(5)javax.servlet.jsp.PageContext: Http页面上下文

如何从ServletActionContext里取得Servlet的相关对象:

<1>取得HttpServletRequest对象: HttpServletRequest request= ServletActionContext. getRequest();

<2>取得HttpSession对象: HttpSession session= ServletActionContext. getRequest().getSession();

3. ServletActionContext和ActionContext联系

ServletActionContext和ActionContext有着一些重复的功能,在我们的Action中,该如何去抉择呢?我们遵循的原则是:如果ActionContext能够实现我们的功能,那最好就不要使用ServletActionContext,让我们的Action尽量不要直接去访问Servlet的相关对象.

注意：在使用ActionContext时有一点要注意:不要在Action的构造函数里使用ActionContext.getContext(),因为这个时候ActionContext里的一些值也许没有设置,这时通过ActionContext取得的值也许是null；同样，HttpServletRequest req= ServletActionContext.getRequest()也不要放在构造函数中，也不要直接将req作为类变量给其赋值。至于原因，我想是因为前面讲到的static ThreadLocal actionContext= new ActionContextThreadLocal()，从这里我们可以看出ActionContext是线程安全的，而ServletActionContext继承自ActionContext，所以ServletActionContext也线程安全，线程安全要求每个线程都独立进行，所以req的创建也要求独立进行，所以ServletActionContext.getRequest()这句话不要放在构造函数中，也不要直接放在类中，而应该放在每个具体的方法体中(eg：login()、queryAll()、insert()等)，这样才能保证每次产生对象时独立的建立了一个req。

4. struts2中获得request、response和session

方法一：使用org.apache.struts2.ActionContext类，通过它的静态方法getContext()获取当前Action的上下文对象。

ActionContext ctx= ActionContext.getContext();

ctx.put("liuwei","andy");//request.setAttribute("liuwei","andy");

Map session= ctx.getSession();//session

HttpServletRequest request= ctx.get(org.apache.struts2.StrutsStatics.HTTP_REQUEST);

HttpServletResponse response= ctx.get(org.apache.struts2.StrutsStatics.HTTP_RESPONSE);

细心的朋友可以发现这里的session是个Map对象,在Struts2中底层的session都被封装成了Map类型.我们可以直接操作这个Map对象进行对session的写入和读取操作,而不用去直接操作HttpSession对象.

方法二：使用org.apache.struts2.ServletActionContext类

public class UserAction extends ActionSupport{

private HttpServletRequest req;

// private HttpServletRequest req= ServletActionContext.getRequest();这条语句放在这个位置是错误的，同样把这条语句放在构造方法中也是错误的。

req= ServletActionContext.getRequest();//req的获得必须在具体的方法中实现

req.getSession().setAttribute("user", user);

req= ServletActionContext.getRequest();//req的获得必须在具体的方法中实现

req.getSession().setAttribute("uList", uList);

(2)IoC方式(即使用Struts2 Aware拦截器)

要使用IoC方式，我们首先要告诉IoC容器(Container)想取得某个对象的意愿，通过实现相应的接口做到这点。

public class UserAction extends ActionSupport implements SessionAware, ServletRequestAware, ServletResponseAware{

private HttpServletRequest request;

private HttpServletResponse response;

public void setServletRequest(HttpServletRequest request){

public void setServletResponse(HttpServletResponse response){

HttpSession session= request.getSession();

为了让用户开发的Action类更加规范，Struts2提供了一个Action接口，这个接口定义了Struts2的Action处理类应该实现的规范。下面是标准Action接口的代码：

//定义Action接口里包含的一些结果字符串

public static final String ERROR="error";

public static final String INPUT="input";

public static final String LOGIN="login";

public static final String NONE="none";

public static final String SUCCESS="success";

//定义处理用户请求的execute()方法

public String execute() throws Exception;

上面的Action接口里只定义了一个execute()方法，该接口规范规定了Action类应该包含一个execute()方法，该方法返回一个字符串，此外，该接口还定义了5个字符串常量，他的作用是统一execute()方法的返回值。

例如，当Action类处理用户处理成功后，有人喜欢返回welcome字符串，有人喜欢返回success字符串，如此不利于项目的统一管理，Struts2的Action接口定义加上了如上的5个字符串常量：ERROR，NONE，INPUT，LOGIN，SUCCESS等，分别代表了特定的含义。当然，如果开发者依然希望使用特定的字符串作为逻辑视图名，开发者依然可以返回自己的视图名。

另外，Struts2还为Action接口提供了一个实现类：ActionSupport，下面是该实现类的代码：

package com.opensymphony.xwork2;

import com.opensymphony.xwork2.inject.Container;

import com.opensymphony.xwork2.inject.Inject;

import com.opensymphony.xwork2.util.ValueStack;

import com.opensymphony.xwork2.util.logging.Logger;

import com.opensymphony.xwork2.util.logging.LoggerFactory;

import java.util.ResourceBundle;

* Provides a default implementation for the most common actions.

* See the documentation for all the interfaces this class implements for more detailed information.

public class ActionSupport implements Action, Validateable, ValidationAware, TextProvider, LocaleProvider, Serializable{

protected static Logger LOG= LoggerFactory.getLogger(ActionSupport.class);

private final ValidationAwareSupport validationAware= new ValidationAwareSupport();

private transient TextProvider textProvider;

public void setActionErrors(Collection<String> errorMessages){

validationAware.setActionErrors(errorMessages);

public Collection<String> getActionErrors(){

return validationAware.getActionErrors();

public void setActionMessages(Collection<String> messages){

validationAware.setActionMessages(messages);

public Collection<String> getActionMessages(){

return validationAware.getActionMessages();

*@deprecated Use{@link#getActionErrors()}.

public Collection<String> getErrorMessages(){

*@deprecated Use{@link#getFieldErrors()}.

public Map<String, List<String>> getErrors(){

public void setFieldErrors(Map<String, List<String>> errorMap){

validationAware.setFieldErrors(errorMap);

public Map<String, List<String>> getFieldErrors(){

return validationAware.getFieldErrors();

ActionContext ctx= ActionContext.getContext();

LOG.debug("Action context not initialized");

public boolean hasKey(String key){

return getTextProvider().hasKey(key);

public String getText(String aTextName){

return getTextProvider().getText(aTextName);

public String getText(String aTextName, String defaultValue){

return getTextProvider().getText(aTextName, defaultValue);

public String getText(String aTextName, String defaultValue, String obj){

return getTextProvider().getText(aTextName, defaultValue, obj);

public String getText(String aTextName, List<Object> args){

return getTextProvider().getText(aTextName, args);

public String getText(String key, String[] args){

return getTextProvider().getText(key, args);

public String getText(String aTextName, String defaultValue, List<Object> args){

return getTextProvider().getText(aTextName, defaultValue, args);

public String getText(String key, String defaultValue, String[] args){

return getTextProvider().getText(key, defaultValue, args);

public String getText(String key, String defaultValue, List<Object> args, ValueStack stack){

return getTextProvider().getText(key, defaultValue, args, stack);

public String getText(String key, String defaultValue, String[] args, ValueStack stack){

return getTextProvider().getText(key, defaultValue, args, stack);

public ResourceBundle getTexts(){

return getTextProvider().getTexts();

public ResourceBundle getTexts(String aBundleName){

return getTextProvider().getTexts(aBundleName);

public void addActionError(String anErrorMessage){

validationAware.addActionError(anErrorMessage);

public void addActionMessage(String aMessage){

validationAware.addActionMessage(aMessage);

public void addFieldError(String fieldName, String errorMessage){

validationAware.addFieldError(fieldName, errorMessage);

//默认Input方法，直接访问input字符串

public String input() throws Exception{

public String doDefault() throws Exception{

* A default implementation that does nothing an returns"success".

* Subclasses should override this method to provide their business logic.

* See also{@link com.opensymphony.xwork2.Action#execute()}.

*@return returns{@link#SUCCESS}

*@throws Exception can be thrown by subclasses.

//默认处理用户请求的方法，直接返回SUCCESS字符串

public String execute() throws Exception{

public boolean hasActionErrors(){

return validationAware.hasActionErrors();

public boolean hasActionMessages(){

return validationAware.hasActionMessages();

return validationAware.hasErrors();

public boolean hasFieldErrors(){

return validationAware.hasFieldErrors();

* Clears field errors. Useful for Continuations and other situations

* where you might want to clear parts of the state on the same action.

public void clearFieldErrors(){

validationAware.clearFieldErrors();

* Clears action errors. Useful for Continuations and other situations

* where you might want to clear parts of the state on the same action.

public void clearActionErrors(){

validationAware.clearActionErrors();

* Clears messages. Useful for Continuations and other situations

* where you might want to clear parts of the state on the same action.

validationAware.clearMessages();

* Clears all errors. Useful for Continuations and other situations

* where you might want to clear parts of the state on the same action.

validationAware.clearErrors();

* Clears all errors and messages. Useful for Continuations and other situations

* where you might want to clear parts of the state on the same action.

public void clearErrorsAndMessages(){

validationAware.clearErrorsAndMessages();

* A default implementation that validates nothing.

* Subclasses should override this method to provide validations.

public Object clone() throws CloneNotSupportedException{

*<!-- START SNIPPET: pause-method-->

* Stops the action invocation immediately(by throwing a PauseException) and causes the action invocation to return

* the specified result, such as{@link#SUCCESS},{@link#INPUT}, etc.

* The next time this action is invoked(and using the same continuation ID), the method will resume immediately

* after where this method was called, with the entire call stack in the execute method restored.

* Note: this method can<b>only</b> be called within the{@link#execute()} method.

*<!-- END SNIPPET: pause-method-->

*@param result the result to return- the same type of return value in the{@link#execute()} method.

public void pause(String result){

* If called first time it will create{@link com.opensymphony.xwork2.TextProviderFactory},

* inject dependency(if{@link com.opensymphony.xwork2.inject.Container} is accesible) into in,

* then will create new{@link com.opensymphony.xwork2.TextProvider} and store it in a field

* for future references and at the returns reference to that field

*@return reference to field with TextProvider

private TextProvider getTextProvider(){

TextProviderFactory tpf= new TextProviderFactory();

textProvider= tpf.createInstance(getClass(), this);

public void setContainer(Container container){

正如上面代码中的，ActionSupport是一个默认的Action实现类，该类里已经提供了许多默认方法，这些方法包括获取国际化信息的方法、数据校验的方法、默认的处理用户请求的方法等，实际上，ActionSupport是Struts2的默认的Action处理类，如果让开发者的Action类继承该ActionSupport类，则会大大简化Action的开发。

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