一个小框架的形成原理（一）

以下是本人在学习过程中做的一点点小小的总结，在这里留个副本！

现有代码存在的问题：

为了解决每个业务模块对应一个Servlet，Servlet过多的问题

解决办法：

使用一个新的Servlet，汇总了所有的业务模块Servlet，增加逻辑判断，具体调用哪个业务Servlet

public class ServletAction extends HttpServlet {

//未抽取之前；

protected void service(HttpServletRequest request, HttpServletResponse response)

throws ServletException, IOException {

String path = request.getServletPath();

if(path.indexOf("/userServlet.action") >=0 ){

//userService.getList(name);

request.setAttribute("user", "user");

this.getServletContext().getRequestDispatcher("/user/user_list.jsp").forward(request, response);

}

if(path.indexOf("/roleServlet.action") >= 0) {

//roleService.getList();

request.setAttribute("role", "role");

this.getServletContext().getRequestDispatcher("/user/role_list.jsp").forward(request, response);

}

该汇总的Servlet在web.xml中注册时，匹配多个，所有的Servlet路径；

<servlet-name>ActionServlet</servlet-name>

<servlet-class>com.bjsxt.struts.ActionServlet</servlet-class>

</servlet>

<servlet-mapping>

<servlet-name>ActionServlet</servlet-name>

<url-pattern>/role/roleServlet.action</url-pattern>

</servlet-mapping>

<servlet-mapping>

<servlet-name>ActionServlet</servlet-name>

<url-pattern>/user/userServlet.action</url-pattern>

</servlet-mapping>

抽取汇总的ServletAction：

各业务Servlet中重复的一些业务代码抽取出来，成为一个单独的类UserAction, RoleAction

同时，forward的页面转向的Url也可以从这些单独的类中返回；

这些单独的类拥有同一个方法execute(),返回值为在forward的页面转向的Url，该方法中执行各自的业务逻辑，由此，抽象出他们共同的接口Iaction;

public interface IAction {

public String execute(HttpServletRequest request, HttpServletResponse response)

throws ServletException, IOException ;

}

public class UserAction implements IAction{

public String execute(HttpServletRequest request,

HttpServletResponse response) throws ServletException, IOException {

//roleService.getList(name);

request.setAttribute("role", "role");

return "/user/user_list.jsp";

}

public class RoleAction implements IAction {

public String execute(HttpServletRequest request,

HttpServletResponse response) throws ServletException, IOException {

//userService.getList(name);

request.setAttribute("user", "user");

return "/user/role_list.jsp";

}

在汇总的ServletAction中只需要有一个IAction的引用，指向不同的子类对象；

public class ServletAction extends HttpServlet {

// 抽取以后;

protected void service(HttpServletRequest request, HttpServletResponse response)

throws ServletException, IOException {

String path = request.getServletPath();

if(path.indexOf("/userServlet.action") >=0 ){

IAction action = new UserAction();

String url = action.execute(request, response);

this.getServletContext().getRequestDispatcher(url).forward(request, response);

}

if(path.indexOf("/roleServlet.action") >= 0) {

IAction action = new UserAction();

String url = action.execute(request, response);

this.getServletContext().getRequestDispatcher(url).forward(request, response);

}

由于每增加一个业务逻辑Action，都需要在汇总的ServletAction中进行判断，代码冗余繁琐，所以需要动态调用每个Action；

实现动态调用的思路：

得到一个map,key里面存放所有的ServletPath，value存放对应的类及jsp;

（以前我们实现动态调用使用反射机制）

分析现状：得到每个ServletPath，根据每个ServletPath映射到不同的Action,从而取得要转向的页面；

解决办法：写一个struts-config.xml配置文件，定义每个ServletPath(web.xml中的url-patten)，及对应的Servlet类（需要调用的Action类即子类对象），及对应的转向页面；

<?xml version="1.0" encoding="UTF-8"?>

<action-mappings>

</action-mappings>

如何解析这个xml文件呢？

使用jdom API,新建一个类XMLReader，其中定义read()方法；

引入jdom .jar文件

public class XMLReader {

//将xml文件中的一个标签元素及其属性存储到一个Map中；

public static void read() {

SAXBuilder builder = new SAXBuilder();

Document doc = null;

Map map = new HashMap();

try {

doc = builder.build(Thread.currentThread().getContextClassLoader()

.getResourceAsStream("struts-config.xml"));

Element e = doc.getRootElement();

System.out.println(e);

List list = e.getChildren();

for(Iterator i= list.iterator(); i.hasNext();) {

ActionMapping am = new ActionMapping();

Element element = (Element)i.next();

am.setPath(element.getAttributeValue("path"));

am.setType(element.getAttributeValue("type"));

am.setForward(element.getAttributeValue("forward"));

//把一个ActionMapping放进Map中；使用put()方法；

map.put(element.getAttributeValue("path"), am);

}

} catch (JDOMException e1) {

// TODO Auto-generated catch block

e1.printStackTrace();

} catch (IOException e1) {

// TODO Auto-generated catch block

e1.printStackTrace();

}

} 将解析得到的document,element的值放入一个map中；

为了使这个类只被ActionServlet调用一次，载入内存，其他任何类不得调用，重构这个XMLReader类的代码：

map设置为静态成员变量；

如果不采用在tomcat启动的时候把XMLReader载入内存的方式的话，使用什么方法呢？

因为XMLReader运行在JVM和Tomcat下的调用机制是不同的，JVM是不需要用到该类就载入内存，而tomcat是用到该类才载入内存；

import org.jdom.JDOMException;

import org.jdom.input.SAXBuilder;

public class XMLReader {

private static Map map = new HashMap();

private static final XMLReader xr = new XMLReader();

private XMLReader(){

read();

}

public static XMLReader getInstance() {

return xr;

}

//将xml文件中的一个标签元素及其属性存储到一个Map中；

private void read() {

SAXBuilder builder = new SAXBuilder();

Document doc = null;

try {

doc = builder.build(Thread.currentThread().getContextClassLoader()

.getResourceAsStream("struts-config.xml"));

Element e = doc.getRootElement();

System.out.println(e);

List list = e.getChildren();

for(Iterator i= list.iterator(); i.hasNext();) {

ActionMapping am = new ActionMapping();

Element element = (Element)i.next();

am.setPath(element.getAttributeValue("path"));

am.setType(element.getAttributeValue("type"));

am.setForward(element.getAttributeValue("forward"));

//把一个ActionMapping放进Map中；使用put()方法；

map.put(element.getAttributeValue("path"), am);

}

} catch (JDOMException e1) {

// TODO Auto-generated catch block

e1.printStackTrace();

} catch (IOException e1) {

// TODO Auto-generated catch block

e1.printStackTrace();

}

//定义一个根据key得到map中的值的方法；

public static ActionMapping getActionMapping(String path) {

return (ActionMapping)map.get(path);

}

public static void main(String[] args) {

getInstance().read();

}

ActionServlet调用XMLReader的代码重构；

// 调用XMLReader;

protected void service(HttpServletRequest request, HttpServletResponse response)

throws ServletException, IOException {

String path = request.getServletPath();

ActionMapping am = XMLReader.getActionMapping(path);

String forward = am.getForward() ;

String type = am.getType();

IAction action = null;

try {

action = (IAction)Class.forName(type).newInstance();

action.execute(request, response);

} catch (InstantiationException e) {

// TODO Auto-generated catch block

e.printStackTrace();

} catch (IllegalAccessException e) {

// TODO Auto-generated catch block

e.printStackTrace();

} catch (ClassNotFoundException e) {

// TODO Auto-generated catch block

e.printStackTrace();

}

this.getServletContext().getRequestDispatcher(forward).forward(request, response);

}

以后如果增加新的业务，只需要增加Action类，配置文件中配置好就可以了

现在存在的问题：

直接Forward出去；用户想更灵活，在Action中定义转向的页面；

业务中不同的条件forward到不同的页面怎么办；

办法：改造配置文件中的forward属性

<?xml version="1.0" encoding="UTF-8"?>

<action-mappings>

</action>

</action>

</action-mappings>

修改ActionMapping：

package com.bjsxt.struts;

import java.util.Map;

public class ActionMapping {

private String path;

private String type;

private Map map;

public String getPath() {

return path;

}

public void setPath(String path) {

this.path = path;

}

public String getType() {

return type;

}

public void setType(String type) {

this.type = type;

}

public Map getMap() {

return map;

}

public void setMap(Map map) {

this.map = map;

}

修改读取XML的类XMLReader：

//将xml文件中的一个标签元素及其属性存储到一个Map中；

private void read() {

SAXBuilder builder = new SAXBuilder();

Document doc = null;

try {

doc = builder.build(Thread.currentThread().getContextClassLoader()

.getResourceAsStream("struts-config.xml"));

Element e = doc.getRootElement();

System.out.println(e);

List list = e.getChildren();

for(Iterator i= list.iterator(); i.hasNext();) {

ActionMapping am = new ActionMapping();

Element element = (Element)i.next();

am.setPath(element.getAttributeValue("path"));

am.setType(element.getAttributeValue("type"));

//am.setForward(element.getAttributeValue("forward"));

List forward = element.getChildren();

Map m = new HashMap();

for(Iterator t= forward.iterator(); t.hasNext();) {

Element forwardemle = (Element)t.next();

m.put(forwardemle.getAttributeValue("name"), forwardemle.getAttributeValue("path"));

}

//把一个ActionMapping放进Map中；使用put()方法；

am.setMap(m);

map.put(element.getAttributeValue("path"), am);

}

} catch (JDOMException e1) {

// TODO Auto-generated catch block

e1.printStackTrace();

} catch (IOException e1) {

// TODO Auto-generated catch block

e1.printStackTrace();

}

修改ServletAction，以前是通过Map中的ActionMapping的getPath()转向，改为通过UserAction返回的Path进行forward转向；

// 调用XMLReader;

protected void service(HttpServletRequest request, HttpServletResponse response)

throws ServletException, IOException {

String path = request.getServletPath();

ActionMapping am = XMLReader.getActionMapping(path);

//String forward = am.getForward() ;

String type = am.getType();

IAction action = null;

String url = null;

try {

action = (IAction)Class.forName(type).newInstance();

url = action.execute(request, response);

} catch (InstantiationException e) {

// TODO Auto-generated catch block

e.printStackTrace();

} catch (IllegalAccessException e) {

// TODO Auto-generated catch block

e.printStackTrace();

} catch (ClassNotFoundException e) {

// TODO Auto-generated catch block

e.printStackTrace();

}

this.getServletContext().getRequestDispatcher(url).forward(request, response);

}

修改UserAction，增加判断转向逻辑；

public String execute(HttpServletRequest request,

HttpServletResponse response) throws ServletException, IOException {

//roleService.getList(name);

request.setAttribute("role", "role");

String path = request.getServletPath();

//需要得到ActionMapping；

ActionMapping am = XMLReader.getActionMapping(path);

//forward的两个属性放到map中了；

Map m = am.getMap();

if(true) {

return(String) m.get("failure");

}*/

return (String)m.get("sucess");

}

存在的问题：

每一个Action，如UserAction都要得到ActionMapping，麻烦；

办法：

ActionServlet中存在ActionMapping，把它当作参数传到UserAction中；

public String execute(HttpServletRequest request,

HttpServletResponse response, ActionMapping am) throws ServletException, IOException {

//roleService.getList(name);

request.setAttribute("role", "role");

String path = request.getServletPath();

/*if(true) {

return(String) m.get("failure");

}*/

//return (String)am.getMap().get("sucess");

//改造ActionMapping类，增加getPath(String path)方法，得到Map中的getPath();

/*public String getPath(String path) {

return (String)map.get(path);

}*/

return am.getPath(path);

存在的问题：

sendRedirect不好用了

办法:

重新设置配置文件；

<?xml version="1.0" encoding="UTF-8"?>

<action-mappings>

</action>

</action>

</action-mappings>

由于Forward有三个属性，直接放在Map中不合适了，所以增加ActionForward类：

package com.bjsxt.struts;

public class ActionForward {

private String name;

private String path;

private boolean redirect;

public String getName() {

return name;

}

public void setName(String name) {

this.name = name;

}

public String getPath() {

return path;

}

public void setPath(String path) {

this.path = path;

}

public boolean isRedirect() {

return redirect;

}

public void setRedirect(boolean redirect) {

this.redirect = redirect;

}

修改XMLReader：

private void read() {

SAXBuilder builder = new SAXBuilder();

Document doc = null;

try {

doc = builder.build(Thread.currentThread().getContextClassLoader()

.getResourceAsStream("struts-config.xml"));

Element e = doc.getRootElement();

System.out.println(e);

List list = e.getChildren();

for(Iterator i= list.iterator(); i.hasNext();) {

ActionMapping am = new ActionMapping();

Element element = (Element)i.next();

am.setPath(element.getAttributeValue("path"));

am.setType(element.getAttributeValue("type"));

//am.setForward(element.getAttributeValue("forward"));

List forward = element.getChildren();

Map m = new HashMap();

for(Iterator t= forward.iterator(); t.hasNext();) {

Element forwardemle = (Element)t.next();

ActionForward actionForward = new ActionForward();

actionForward.setName(forwardemle.getAttributeValue("name"));

actionForward.setPath(forwardemle.getAttributeValue("path"));

actionForward.setRedirect(Boolean.valueOf(forwardemle.getAttributeValue("redirect")));

m.put(forwardemle.getAttributeValue("name"),actionForward);

}

//把一个ActionMapping放进Map中；使用put()方法；

am.setMap(m);

map.put(element.getAttributeValue("path"), am);

}

} catch (JDOMException e1) {

// TODO Auto-generated catch block

e1.printStackTrace();

} catch (IOException e1) {

// TODO Auto-generated catch block

e1.printStackTrace();

}

修改UserAction增加返回值；

UserAction应该不只是返回URL，还应该返回isRedirect，所以，它应该返回一个ActionForward对象：

public ActionForward execute(HttpServletRequest request,

HttpServletResponse response, ActionMapping am) throws ServletException, IOException {

//roleService.getList(name);

request.setAttribute("role", "role");

//String path = request.getServletPath();

//改造ActionMapping类，增加getPath(String path)方法，得到Map中的getPath();

/*public ActionMapping getPath(String path) {

return (String)map.get(path);

}*/

return am.getPath("success");

}

根据传过来的ActionForward对象，ServletAction判断是forward还是sendRedirect?

protected void service(HttpServletRequest request,

HttpServletResponse response) throws ServletException, IOException {

String path = request.getServletPath();

ActionMapping am = XMLReader.getActionMapping(path);

// String forward = am.getForward() ;

String type = am.getType();

IAction action = null;

ActionForward actionForward = null;

try {

action = (IAction) Class.forName(type).newInstance();

actionForward = action.execute(request, response);

} catch (InstantiationException e) {

// TODO Auto-generated catch block

e.printStackTrace();

} catch (IllegalAccessException e) {

// TODO Auto-generated catch block

e.printStackTrace();

} catch (ClassNotFoundException e) {

// TODO Auto-generated catch block

e.printStackTrace();

}

if (actionForward.isRedirect()) {

response.sendRedirect(request.getContextPath()

+ actionForward.getPath());

} else {

this.getServletContext().getRequestDispatcher(

actionForward.getPath()).forward(request, response);

}

存在的问题：明天解决

解决request对象依赖过多的问题：

如何让它自动映射，不需要从request.getParameter()拿数据.

posted on 2009-04-11 21:48 西西里阅读(385) 评论(0) 编辑收藏

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一个小框架的形成原理（一）