package cn.itcast.config;import org.apache.log4j.Logger;
import org.dom4j.Document;
import org.dom4j.DocumentException;
import org.dom4j.Element;
import org.dom4j.io.SAXReader;import java.io.InputStream;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;/*** Created by zhen on 2017-08-04.* 读取struts.xml配置信息*/
public class ConfigurationManager {private static final Logger logger = Logger.getLogger(ConfigurationManager.class);//读取Interceptorpublic static List<String> getInterceptors(){List<String> interceptors = null;SAXReader saxReader = new SAXReader();InputStream inputStream = ConfigurationManager.class.getResourceAsStream("/struts.xml");Document document = null;try {document = saxReader.read(inputStream);} catch (DocumentException e) {logger.error(e.getMessage());throw new RuntimeException("配置文件解析异常" ,e);}String xpath = "//interceptor";List<Element> list = document.selectNodes(xpath);if(list != null && list.size() > 0){interceptors = new ArrayList<String>();for(Element ele: list){String className = ele.attributeValue("class");interceptors.add(className);}}return interceptors;}//读取Constantpublic static String getConstant(String name){String value = null;SAXReader saxReader = new SAXReader();InputStream is = ConfigurationManager.class.getResourceAsStream("/struts.xml");Document document = null;try {document = saxReader.read(is);} catch (DocumentException e) {logger.error(e.getMessage());throw new RuntimeException("配置文件解析异常" ,e);}String xPath = "//constant[@name='" + name + "']";List<Element> ele = document.selectNodes(xPath);if(ele != null && ele.size() > 0){value = ele.get(0).attributeValue("value");}return value;}//读取Actionpublic static Map<String, ActionConfig> getActions(){Map<String, ActionConfig> actions = null;SAXReader saxReader = new SAXReader();InputStream is = ConfigurationManager.class.getResourceAsStream("/struts.xml");Document document = null;try {document = saxReader.read(is);} catch (DocumentException e) {logger.error(e.getMessage());throw new RuntimeException("配置文件解析异常" ,e);}String xPath = "//action";List<Element> list = document.selectNodes(xPath);if(list != null && list.size() > 0){actions = new HashMap<String, ActionConfig>();for(Element element : list){ActionConfig actionConfig = new ActionConfig();String name = element.attributeValue("name");String method = element.attributeValue("method");String className = element.attributeValue("class");Map<String, String> results = null;List<Element> resultElements = element.elements("result");if(resultElements != null && resultElements.size() > 0){results = new HashMap();for(Element ele: resultElements){String resultName = ele.attributeValue("name");String resultValue = ele.getTextTrim();results.put(resultName, resultValue);}}actionConfig.setName(name);actionConfig.setMethod(method == null || method.trim().equals("") ? "execute" : method.trim());actionConfig.setClassName(className);actionConfig.setResults(results);actions.put(name, actionConfig);}}return actions;}}

package cn.itcast.invocation;import cn.itcast.config.ActionConfig;
import cn.itcast.context.ActionContext;
import cn.itcast.interceptor.Interceptor;
import org.apache.log4j.Logger;import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.lang.reflect.Method;
import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;/*** Created by zhen on 2017-08-06.*/
public class ActionInvocation {private static final Logger logger = Logger.getLogger(ActionInvocation.class);private Iterator<Interceptor> interceptors;private Object action;private ActionConfig actionConfig;private ActionContext actionContext;private String resultUrl;public ActionContext getActionContext() {return actionContext;}public ActionInvocation(List<String> classNames, ActionConfig actionConfig, HttpServletRequest request, HttpServletResponse response){//装载Interceptor链if(classNames != null && classNames.size() > 0){List<Interceptor> interceptorList = new ArrayList<Interceptor>();for(String className : classNames){try {Interceptor interceptor = (Interceptor) Class.forName(className).newInstance();interceptor.init();interceptorList.add(interceptor);} catch (Exception e) {logger.error(e.getMessage());throw new RuntimeException("创建Interceptor失败，Interceptor Name:" + className ,e);}}interceptors =  interceptorList.iterator();}//准备action实例this.actionConfig = actionConfig;try {action = Class.forName(actionConfig.getClassName()).newInstance();} catch (Exception e) {logger.error(e.getMessage());throw new RuntimeException("创建Action实例失败！" + actionConfig.getClass(), e);}//准备数据中心actionContext = new ActionContext(request, response, action);}public String invoke(){if(interceptors != null && interceptors.hasNext() && resultUrl == null){Interceptor interceptor = interceptors.next();resultUrl = interceptor.invoke(this);}else{try{Method executeMethod = Class.forName(actionConfig.getClassName()).getMethod(actionConfig.getMethod());resultUrl = (String) executeMethod.invoke(action);}catch(Exception ex){logger.error(ex.getMessage());throw new RuntimeException("您配置的action方法不存在" + actionConfig.getClassName());}}return resultUrl;}
}

package cn.itcast.filter;import cn.itcast.config.ActionConfig;
import cn.itcast.config.ConfigurationManager;
import cn.itcast.context.ActionContext;
import cn.itcast.invocation.ActionInvocation;
import org.apache.log4j.Logger;
import org.junit.Test;import javax.servlet.*;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.util.List;
import java.util.Map;/*** Created by zhen on 2017-08-06.*/
public class StrutsPrepareAndExecuteFilter implements Filter {private static final Logger logger = Logger.getLogger(StrutsPrepareAndExecuteFilter.class);private List<String> interceptorClassNames;private  String extension;private Map<String, ActionConfig> actionConfigs;public void init(FilterConfig filterConfig) throws ServletException {//装载配置信息interceptorClassNames = ConfigurationManager.getInterceptors();extension = ConfigurationManager.getConstant("struts.action.extension");actionConfigs = ConfigurationManager.getActions();}public static void main(String[] args){Logger logger = Logger.getLogger(StrutsPrepareAndExecuteFilter.class);}public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {//执行HttpServletRequest request = (HttpServletRequest) servletRequest;HttpServletResponse response = (HttpServletResponse) servletResponse;String urlPath = request.getRequestURI();if(!urlPath.endsWith(extension)){filterChain.doFilter(request, response);return;}String actionName = urlPath.substring(urlPath.lastIndexOf("/") + 1).replace("." + extension, "");ActionConfig actionConfig = actionConfigs.get(actionName);if(actionConfig == null){throw new RuntimeException("找不到对应的action！" + actionName);}ActionInvocation actionInvocation = new ActionInvocation(interceptorClassNames, actionConfig, request, response);String result = actionInvocation.invoke();String dispatcherPath = actionConfig.getResults().get(result);if(dispatcherPath == null || "".equals(dispatcherPath)){throw new RuntimeException("找不到对应的返回路径！");}request.getRequestDispatcher(dispatcherPath).forward(request, response);ActionContext.tl.remove();}public void destroy() {}
}

struts2模拟1、关注点分离思想。类似java中的解耦合，插拔。将功能拆分成各个拦截器实现。拦截器运行过程中拼接出想要的功能。
2、MVC思想。 filter-C Action-M jsp_url-V需要掌握知识：XML解析，Xpath表达式（dom4j）Servlet技术java内省（BeanUtils）ThreadLocal线程本地化类递归调用需要补充的知识：dom4j解析xpath语法获取资源文件路径理解：对于值栈的模拟不要拘泥于数组，也可以使用现有的类进行封装，比如使用ArrayList模拟。经常递归调用使用的局部变量可以放在循环外或者说是方法外。