StrutsRequestWrapper详解

查看一下StrutsRequestWrapper的源代码，本人将其中的英文注释转为中文

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请求用这个类，他提供了简单的JSTL的可达性，这是因为JSTL与请求属性与请求属性在一起工作 * 所以这个类代表值栈，除了在少数情况下需要防止无限循环的发生，即，不要让任何属性的名字中带有#，#代表了值栈，他可能导致无限循环 * 例如在这种情况下可能发生无限循环 * request.getAttribute("#attr.foo"). */public class StrutsRequestWrapper extends HttpServletRequestWrapper {    /**     * The constructor     * @param req The request     */    public StrutsRequestWrapper(HttpServletRequest req) {        super(req);    }    /**     * 获取对象，如果不存在，那么在值栈中找     * @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;    }}

由源代码可以看到的是HttpServletRequestWrapper，所以先来了解一下HttpServletRequestWrapper.

Wrapper是包装的意思，所以HttpServletRequestWrapper的字面意思就是对HttpServletRequest的包装。首先查看一下HttpServletRequestWrapper的源代码：

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  * @sincev 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();    }    }

这个HttpServletRequestWrapper就是对HttpServletRequest的包装实现。其实这个类的作用与HttpServletRequest的·作用类似。

通过上面源码的了解，可以看到StrutsRequestWrapper是在struts2框架中对HttpServletRequestWrapper类的包装，以使其得到扩展，在Struts2中，扩展后的HttpServletRequest类有了一个方法

public Object getAttribute(String s) 

这个方法的作用是在servlet的Request的作用域中获得属性名为s的属性值，如果Request作用域中不存在，那么将到Struts2的值栈中查找。

它们应用了设计模式中的装饰者模式。

它们之间的关系如上图所示