Struts2实现接口和继承ActionSupport基类（转）

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：

package ppp;

public interface Action {

    //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.io.Serializable;
import java.util.Collection;
import java.util.List;
import java.util.Locale;
import java.util.Map;
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;
private Container container;

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()}.
*/
@Deprecated
public Collection<String> getErrorMessages() {
return getActionErrors();
}
/**
* @deprecated Use {@link #getFieldErrors()}.
*/
@Deprecated
public Map<String, List<String>> getErrors() {
return getFieldErrors();
}
//设置表单域校验错误信息
public void setFieldErrors(Map<String, List<String>> errorMap) {
validationAware.setFieldErrors(errorMap);
}
//返回表单域错误校验信息
public Map<String, List<String>> getFieldErrors() {
return validationAware.getFieldErrors();
}
//控制locale的相关信息
public Locale getLocale() {
ActionContext ctx = ActionContext.getContext();
if (ctx != null) {
return ctx.getLocale();
} else {
LOG.debug("Action context not initialized");
return null;
}
}
public boolean hasKey(String key) {
return getTextProvider().hasKey(key);
}
public String getText(String aTextName) {
return getTextProvider().getText(aTextName);
}
//返回国际化信息的方法
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);
}
//用于访问国际化资源包的方法
public ResourceBundle getTexts() {
return getTextProvider().getTexts();
}
public ResourceBundle getTexts(String aBundleName) {
return getTextProvider().getTexts(aBundleName);
}
//添加错误信息
public void addActionError(String anErrorMessage) {
validationAware.addActionError(anErrorMessage);
}
public void addActionMessage(String aMessage) {
validationAware.addActionMessage(aMessage);
}
添加字段校验的错误信息
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 {
return INPUT;
}
public String doDefault() throws Exception {
return SUCCESS;
}
/**
* A default implementation that does nothing an returns "success".
* <p/>
* Subclasses should override this method to provide their business logic.
* <p/>
* 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 {
return SUCCESS;
}
public boolean hasActionErrors() {
return validationAware.hasActionErrors();
}
public boolean hasActionMessages() {
return validationAware.hasActionMessages();
}
public boolean hasErrors() {
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.
*/
public void clearMessages() {
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.
*/
public void clearErrors() {
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.
*/
//清理错误信息的方法
public void clearErrorsAndMessages() {
validationAware.clearErrorsAndMessages();
}
/**
* A default implementation that validates nothing.
* Subclasses should override this method to provide validations.
*/
//包含空校验的方法
public void validate() {
}
@Override
public Object clone() throws CloneNotSupportedException {
return super.clone();
}
/**
* <!-- 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.
* <p/>
* <p/>
* 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.
* <p/>
* <p/>
* 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() {
if (textProvider == null) {
TextProviderFactory tpf = new TextProviderFactory();
if (container != null) {
container.inject(tpf);
}
textProvider = tpf.createInstance(getClass(), this);
}
return textProvider;
}
@Inject
public void setContainer(Container container) {
this.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。