StrutsRequestWrapper詳解

查看一下StrutsRequestWrapper的源代碼，本人將其中的英文註釋轉爲中文

package org.apache.struts2.dispatcher;

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletRequestWrapper;

import com.opensymphony.xwork2.ActionContext;
import com.opensymphony.xwork2.util.ValueStack;

/**
 *
 * 所有的request請求用這個類，他提供了簡單的JSTL的可達性，這是因爲JSTL與請求屬性與請求屬性在一起工作
 * 所以這個類代表值棧，除了在少數情況下需要防止無限循環的發生，即，不要讓任何屬性的名字中帶有#，#代表了值棧，他可能導致無限循環
 * 例如在這種情況下可能發生無限循環
 * request.getAttribute("#attr.foo").
 */
public class StrutsRequestWrapper extends HttpServletRequestWrapper {

    /**
     * The constructor
     * @param req The request
     */
    public StrutsRequestWrapper(HttpServletRequest req) {
        super(req);
    }

    /**
     * 獲取對象，如果不存在，那麼在值棧中找
     * @param s The attribute key
     */
    public Object getAttribute(String s) {
        if (s != null && s.startsWith("javax.servlet")) {
            // don't bother with the standard javax.servlet attributes, we can short-circuit this
            // see WW-953 and the forums post linked in that issue for more info
            return super.getAttribute(s);
        }

        ActionContext ctx = ActionContext.getContext();
        Object attribute = super.getAttribute(s);
        if (ctx != null) {
            if (attribute == null) {
                boolean alreadyIn = false;
                Boolean b = (Boolean) ctx.get("__requestWrapper.getAttribute");
                if (b != null) {
                    alreadyIn = b.booleanValue();
                }
    
                // note: we don't let # come through or else a request for
                // #attr.foo or #request.foo could cause an endless loop
                if (!alreadyIn && s.indexOf("#") == -1) {
                    try {
                        // If not found, then try the ValueStack
                        ctx.put("__requestWrapper.getAttribute", Boolean.TRUE);
                        ValueStack stack = ctx.getValueStack();
                        if (stack != null) {
                            attribute = stack.findValue(s);
                        }
                    } finally {
                        ctx.put("__requestWrapper.getAttribute", Boolean.FALSE);
                    }
                }
            }
        }
        return attribute;
    }
}

由源代碼可以看到的是HttpServletRequestWrapper，所以先來了解一下HttpServletRequestWrapper.

Wrapper是包裝的意思，所以HttpServletRequestWrapper的字面意思就是對HttpServletRequest的包裝。首先查看一下HttpServletRequestWrapper的源代碼：

package javax.servlet.http;

import javax.servlet.ServletRequestWrapper;
import java.util.Enumeration;

/**
 * 
 * Provides a convenient implementation of the HttpServletRequest interface that
 * can be subclassed by developers wishing to adapt the request to a Servlet.
 * This class implements the Wrapper or Decorator pattern. Methods default to
 * calling through to the wrapped request object.
 * 
 *
 * @see 	javax.servlet.http.HttpServletRequest
  * @since	v 2.3
 *
 */


public class HttpServletRequestWrapper extends ServletRequestWrapper implements HttpServletRequest {

	/** 
	* Constructs a request object wrapping the given request.
	* @throws java.lang.IllegalArgumentException if the request is null
	*/
    public HttpServletRequestWrapper(HttpServletRequest request) {
	    super(request);
    }
    
    private HttpServletRequest _getHttpServletRequest() {
	return (HttpServletRequest) super.getRequest();
    }

    /**
     * The default behavior of this method is to return getAuthType()
     * on the wrapped request object.
     */

    public String getAuthType() {
	return this._getHttpServletRequest().getAuthType();
    }
   
    /**
     * The default behavior of this method is to return getCookies()
     * on the wrapped request object.
     */
    public Cookie[] getCookies() {
	return this._getHttpServletRequest().getCookies();
    }

    /**
     * The default behavior of this method is to return getDateHeader(String name)
     * on the wrapped request object.
     */
    public long getDateHeader(String name) {
	return this._getHttpServletRequest().getDateHeader(name);
    }
        	
    /**
     * The default behavior of this method is to return getHeader(String name)
     * on the wrapped request object.
     */
    public String getHeader(String name) {
	return this._getHttpServletRequest().getHeader(name);
    }
    
    /**
     * The default behavior of this method is to return getHeaders(String name)
     * on the wrapped request object.
     */
    public Enumeration getHeaders(String name) {
	return this._getHttpServletRequest().getHeaders(name);
    }  

    /**
     * The default behavior of this method is to return getHeaderNames()
     * on the wrapped request object.
     */
  
    public Enumeration getHeaderNames() {
	return this._getHttpServletRequest().getHeaderNames();
    }
    
    /**
     * The default behavior of this method is to return getIntHeader(String name)
     * on the wrapped request object.
     */

     public int getIntHeader(String name) {
	return this._getHttpServletRequest().getIntHeader(name);
    }
    
    /**
     * The default behavior of this method is to return getMethod()
     * on the wrapped request object.
     */
    public String getMethod() {
	return this._getHttpServletRequest().getMethod();
    }
    
    /**
     * The default behavior of this method is to return getPathInfo()
     * on the wrapped request object.
     */
    public String getPathInfo() {
	return this._getHttpServletRequest().getPathInfo();
    }

    /**
     * The default behavior of this method is to return getPathTranslated()
     * on the wrapped request object.
     */

     public String getPathTranslated() {
	return this._getHttpServletRequest().getPathTranslated();
    }

    /**
     * The default behavior of this method is to return getContextPath()
     * on the wrapped request object.
     */
    public String getContextPath() {
	return this._getHttpServletRequest().getContextPath();
    }
    
    /**
     * The default behavior of this method is to return getQueryString()
     * on the wrapped request object.
     */
    public String getQueryString() {
	return this._getHttpServletRequest().getQueryString();
    }
    
    /**
     * The default behavior of this method is to return getRemoteUser()
     * on the wrapped request object.
     */
    public String getRemoteUser() {
	return this._getHttpServletRequest().getRemoteUser();
    }
    
 
    /**
     * The default behavior of this method is to return isUserInRole(String role)
     * on the wrapped request object.
     */
    public boolean isUserInRole(String role) {
	return this._getHttpServletRequest().isUserInRole(role);
    }
    
    
    
    /**
     * The default behavior of this method is to return getUserPrincipal()
     * on the wrapped request object.
     */
    public java.security.Principal getUserPrincipal() {
	return this._getHttpServletRequest().getUserPrincipal();
    }
    
   
    /**
     * The default behavior of this method is to return getRequestedSessionId()
     * on the wrapped request object.
     */
    public String getRequestedSessionId() {
	return this._getHttpServletRequest().getRequestedSessionId();
    }
    
    /**
     * The default behavior of this method is to return getRequestURI()
     * on the wrapped request object.
     */
    public String getRequestURI() {
	return this._getHttpServletRequest().getRequestURI();
    }
	/**
     * The default behavior of this method is to return getRequestURL()
     * on the wrapped request object.
     */
    public StringBuffer getRequestURL() {
	return this._getHttpServletRequest().getRequestURL();
    }
	
    
    /**
     * The default behavior of this method is to return getServletPath()
     * on the wrapped request object.
     */
    public String getServletPath() {
	return this._getHttpServletRequest().getServletPath();
    }
    
    
    /**
     * The default behavior of this method is to return getSession(boolean create)
     * on the wrapped request object.
     */
    public HttpSession getSession(boolean create) {
	return this._getHttpServletRequest().getSession(create);
    }
    
    /**
     * The default behavior of this method is to return getSession()
     * on the wrapped request object.
     */
    public HttpSession getSession() {
	return this._getHttpServletRequest().getSession();
    }
    
    /**
     * The default behavior of this method is to return isRequestedSessionIdValid()
     * on the wrapped request object.
     */ 

    public boolean isRequestedSessionIdValid() {
	return this._getHttpServletRequest().isRequestedSessionIdValid();
    }
     
    
    /**
     * The default behavior of this method is to return isRequestedSessionIdFromCookie()
     * on the wrapped request object.
     */
    public boolean isRequestedSessionIdFromCookie() {
	return this._getHttpServletRequest().isRequestedSessionIdFromCookie();
    }
    
    	  /**
     * The default behavior of this method is to return isRequestedSessionIdFromURL()
     * on the wrapped request object.
     */ 
    public boolean isRequestedSessionIdFromURL() {
	return this._getHttpServletRequest().isRequestedSessionIdFromURL();
    }
    
    /**
     * The default behavior of this method is to return isRequestedSessionIdFromUrl()
     * on the wrapped request object.
     */
    public boolean isRequestedSessionIdFromUrl() {
	return this._getHttpServletRequest().isRequestedSessionIdFromUrl();
    }


    
}

這個HttpServletRequestWrapper就是對HttpServletRequest的包裝實現。其實這個類的作用與HttpServletRequest的·作用類似。

通過上面源碼的瞭解，可以看到StrutsRequestWrapper是在struts2框架中對HttpServletRequestWrapper類的包裝，以使其得到擴展，在Struts2中，擴展後的HttpServletRequest類有了一個方法