• 扩展入口Filter实现：
  

package lab.s2jh.core.web.sitemesh;

import org.sitemesh.DecoratorSelector;
import org.sitemesh.builder.SiteMeshFilterBuilder;
import org.sitemesh.config.ConfigurableSiteMeshFilter;
import org.sitemesh.webapp.WebAppContext;

/**
 * 扩展实现注入基于request参数decorator值进行动态定位装饰器的选择器
 */
public class ParamConfigurableSiteMeshFilter extends ConfigurableSiteMeshFilter {

    protected void applyCustomConfiguration(SiteMeshFilterBuilder builder) {
        //获取原有默认配置装饰选择器
        DecoratorSelector<WebAppContext> defaultDecoratorSelector = builder.getDecoratorSelector();
        //赋给自定义装饰选择器，则自定义规则未匹配时调用默认选择器获取
        builder.setCustomDecoratorSelector(new ParamDecoratorSelector(defaultDecoratorSelector));
    }
}

• 定制装饰选择器实现：
  

package lab.s2jh.core.web.sitemesh;

import java.io.IOException;

import javax.servlet.http.HttpServletRequest;

import org.apache.commons.lang3.StringUtils;
import org.sitemesh.DecoratorSelector;
import org.sitemesh.content.Content;
import org.sitemesh.webapp.WebAppContext;

/**
 * 基于request参数decorator值进行动态定位装饰器的选择器
 * 如果decorator参数有值，则返回"/WEB-INF/views/layouts/" + decorator + ".jsp"作为目标装饰模板页面
 */
public class ParamDecoratorSelector implements DecoratorSelector<WebAppContext> {

    private DecoratorSelector<WebAppContext> defaultDecoratorSelector;

    public ParamDecoratorSelector(DecoratorSelector<WebAppContext> defaultDecoratorSelector) {
        this.defaultDecoratorSelector = defaultDecoratorSelector;
    }

    public String[] selectDecoratorPaths(Content content, WebAppContext context) throws IOException {
        // build decorator based on the request
        HttpServletRequest request = context.getRequest();
        String decorator = request.getParameter("decorator");
        if (StringUtils.isNotBlank(decorator)) {
            //按照参数值返回对应路径下面的jsp装饰模板页码
            return new String[] { "/WEB-INF/views/layouts/" + decorator + ".jsp" };
        }

        // Otherwise, fallback to the standard configuration
        return defaultDecoratorSelector.selectDecoratorPaths(content, context);
    }
}

• 调整web.xml配置：

    <filter>
        <filter-name>sitemeshFilter</filter-name>
        <filter-class>lab.s2jh.core.web.sitemesh.ParamConfigurableSiteMeshFilter</filter-class>
    </filter>
    <filter-mapping>
        <filter-name>sitemeshFilter</filter-name>
        <url-pattern>/*</url-pattern>
    </filter-mapping>

扩展Sitemesh3 DecoratorSelector实现基于请求参数调用装饰模板页面的实现