/**
 * Created by ozc on 2017/4/26.
 *
 * 该类管理着全部的Action
 *
 * 要管理全部的Action，就需要用一个容器来装载这些Action
 *
 * 选择Map集合是最合适的，可以通过key来得到Action，key就是<action name=><action/>中的name属性
 *
 */
public class ActionMappingManager {
    private Map<String, ActionMapping> allAction ;
    public ActionMappingManager() {
        this.allAction = new HashMap<>();
        //读取配置文件信息
        init();
    }
    public void init() {
        /********通过DOM4J读取配置文件信息*********/
        try {
            //得到解析器
            SAXReader saxReader = new SAXReader();
            //读取在类目录下的mystruts.xml文件
            InputStream stream = ActionMappingManager.class.getClassLoader().getResourceAsStream("mystruts.xml");
            //得到代表XML文件的Document对象
            Document document = saxReader.read(stream);
            //通过XPATH直接得到所有的Action节点
            List list = document.selectNodes("//action");
            //得到每个Action节点
            for (int i = 0; i < list.size(); i++) {
                Element action = (Element) list.get(i);
                //把得到每个Action的节点信息封装到ActionMapping中
                ActionMapping actionMapping = new ActionMapping();
                String name = action.attributeValue("name");
                String method = action.attributeValue("method");
                String className = action.attributeValue("className");
                actionMapping.setName(name);
                actionMapping.setMethod(method);
                actionMapping.setClassName(className);
                //得到action节点下的所有result节点
                List results = action.elements("result");
                //得到每一个result节点
                for (int j = 0; j < results.size(); j++) {
                    Element result = (Element) results.get(j);
                    //把得到每个result节点的信息封装到Results中
                    Results results1 = new Results();
                    //得到节点的信息
                    String name1 = result.attributeValue("name");
                    String type = result.attributeValue("type");
                    String page = result.getText();
                    results1.setName(name1);
                    results1.setType(type);
                    results1.setPage(page);
                    //把result节点添加到ActionMapping的集合中
                    actionMapping.getResults().put(name1, results1);
                }
                //最后把得到每个ActionMapping的信息添加到ActionMappingManager中
                allAction.put(name, actionMapping);
            }
        } catch (DocumentException e) {
            new RuntimeException("初始化的时候出错了！“" + e);
        }
    }
    //注意：外界都是通过name来得到对应的Action的，并不会获取得到整个Manager
    public ActionMapping getActionMapping(String name) {
        return allAction.get(name);
    }
}

/**
 * Created by ozc on 2017/4/26.
 *
 *
 * Web容器一启动的时候，该类就应该加载了,在web.xml文件中配置onloadStart
 */
public class ActionServlet extends HttpServlet {
    //该对象封装了所有的XML信息
    ActionMappingManager actionMappingManager ;
    @Override
    public void init() throws ServletException {
        //让ActionMappingManager对象只有一个！
        actionMappingManager = new ActionMappingManager();
    }
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        try {
            //得到用户的uri
            String uri = request.getRequestURI();
            //截取uri的关键部分-----截完应该是login
            uri = uri.substring(uri.lastIndexOf("/") + 1, uri.lastIndexOf("."));
            //通过uri得到配置文件中的action信息
            ActionMapping actionMapping = actionMappingManager.getActionMapping(uri);
            //得到action的类名，方法名
            String className = actionMapping.getClassName();
            String method = actionMapping.getMethod();
            //通过反射创建出Action的对象，调用对应的方法
            Class t = Class.forName(className);
            Object o = t.newInstance();
            //注意：这里的参数是接口的class，不是单纯的request的class，单纯的class是实现类
            Method m = t.getMethod(method, HttpServletRequest.class, HttpServletResponse.class);
            //调用方法,得到标记
            String returnFlag = (String) m.invoke(o, request, response);
            //通过标记得到result的具体信息
            Results result = actionMapping.getResults().get(returnFlag);
            String type = result.getType();
            String page = result.getPage();
            //判断是重定向还是转发，为空就是转发，反则是重定向
            if (type == null) {
                response.sendRedirect(page);
            } else {
                request.getRequestDispatcher(request.getContextPath() + page).forward(request, response);
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        this.doPost(request, response);
    }
}

<!-- 引入struts核心过滤器 -->
    <filter>
        <filter-name>struts2</filter-name>
        <filter-class>org.apache.struts2.dispatcher.ng.filter.StrutsPrepareAndExecuteFilter</filter-class>
    </filter>
    <filter-mapping>
        <filter-name>struts2</filter-name>
        <url-pattern>/*</url-pattern>
    </filter-mapping>

<?xml version="1.0" encoding="UTF-8" ?>
        <!DOCTYPE struts PUBLIC
                "-//Apache Software Foundation//DTD Struts Configuration 2.0//EN"
                "http://struts.apache.org/dtds/struts-2.0.dtd">
<struts>
<package name="hello" extends="struts-default">
    <action name="hello" class="action.HelloAction" method="execute">
        <result name="success">/index.jsp</result>
    </action>
</package>
</struts>