MVC架构探究及其源码兑现(5)-相关组件实现

MVC架构探究及其源码实现(5)-相关组件实现

本文将讨论HandlerMapping，HandlerAdapter，ViewResolver组件类的具体实现。

URLHandlerMapping,利用request中包含的url信息，找到对应Handler对象，URLHandlerMapping是最典型的映射方式。

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package com.google.mvc.web.servlet.handler;  
  
import java.util.Map;  
import java.util.concurrent.ConcurrentHashMap;  
import java.util.concurrent.atomic.AtomicBoolean;  
  
import javax.servlet.http.HttpServletRequest;  
  
import org.apache.log4j.Logger;  
  
import com.google.mvc.web.context.WebApplicationContext;  
import com.google.mvc.web.context.WebApplicationContextAware;  
import com.google.mvc.web.servlet.HandlerMapping;  
import com.google.mvc.web.servlet.mvc.Controller;  
import com.google.mvc.web.servlet.mvc.HttpRequestHandler;  
  
public class URLHandlerMapping implements HandlerMapping, WebApplicationContextAware{  
  
    private static final Logger LOGGER = Logger.getLogger(URLHandlerMapping.class);  
    private WebApplicationContext wac;  
    private Map<String, Object> handlerMap = new ConcurrentHashMap<String, Object>();  
    private AtomicBoolean initialize = new AtomicBoolean(false);  
  
    @Override  
    public void setWebApplicationContext(WebApplicationContext wac) {  
        this.wac = wac;               
    }  
  
    @Override  
    public Object getHandler(HttpServletRequest request) throws Exception {   
        if(LOGGER.isDebugEnabled()){  
            LOGGER.debug("Find handler for request " + request.getServletPath());  
        }  
                  
        if(initialize.compareAndSet(false, true)){  
            Map<String, HttpRequestHandler> map1 = wac.beansOfType(HttpRequestHandler.class);  
            for(String key : map1.keySet()){  
                handlerMap.put(key, map1.get(key));  
            }  
            Map<String, Controller> map2 = wac.beansOfType(Controller.class);  
            for(String key : map2.keySet()){  
                handlerMap.put(key, map2.get(key));  
            }  
        }         
        Object handler = handlerMap.get(getHandlerName(request));  
        if(handler == null){  
            handler = handlerMap.get("404");  
        }  
        return handler;  
    }  
      
    protected String getHandlerName(HttpServletRequest request){  
        String path = request.getServletPath();  
        int index = path.lastIndexOf('/');  
        String handleName = path.substring(index + 1, path.length());  
        return handleName;  
    }  
  
}  

HandlerAdapter用于把不同的Handler对象处理的结果封装成一个统一的对象ModelAndView,以达到逻辑上的一致处理。在这里，我们定义两种Handler类型

Controller：用于处理用户的业务逻辑，并返回具体ModelAndView对象，具体接口定义如下
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1. package com.google.mvc.web.servlet.mvc;
3. import javax.servlet.http.HttpServletRequest;
4. import javax.servlet.http.HttpServletResponse;
6. import com.google.mvc.web.servlet.ModelAndView;
8. public interface Controller {
10. ModelAndView handleRequest(HttpServletRequest request, HttpServletResponse response) throws Exception;
11. }
HttpRequestHandler：用于处理简单的HTTP请求。接口定义如下
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1. package com.google.mvc.web.servlet.mvc;
3. import javax.servlet.http.HttpServletRequest;
4. import javax.servlet.http.HttpServletResponse;
7. public interface HttpRequestHandler {
9. void handleRequest(HttpServletRequest request, HttpServletResponse response) throws Exception;
11. }
我们来看一下HandlerFor404的简单实现。
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1. package com.google.mvc.web.servlet.mvc;
3. import javax.servlet.http.HttpServletRequest;
4. import javax.servlet.http.HttpServletResponse;
6. public class HandlerFor404 implements HttpRequestHandler {
8. @Override
9. public void handleRequest(HttpServletRequest request, HttpServletResponse response) throws Exception {
10. response.sendRedirect("404.html");
11. }
13. }

我们需要为每一种不同的Handler类型指定一种HandlerAdapter，但这不是必须的。
ControllerHandlerAdapter

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package com.google.mvc.web.servlet.mvc;  
  
import javax.servlet.http.HttpServletRequest;  
import javax.servlet.http.HttpServletResponse;  
  
import com.google.mvc.web.servlet.HandlerAdapter;  
import com.google.mvc.web.servlet.ModelAndView;  
  
public class ControllerHandlerAdapter implements HandlerAdapter{  
      
    public boolean supports(Object handler) {  
        return (handler instanceof Controller);  
    }  
  
    public ModelAndView handle(HttpServletRequest request, HttpServletResponse response, Object handler)  
            throws Exception {  
  
        return ((Controller) handler).handleRequest(request, response);  
    }  
  
    public long getLastModified(HttpServletRequest request, Object handler) {  
      
        return -1L;  
    }  
  
}

HttpRequestHandlerAdapter

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package com.google.mvc.web.servlet.mvc;  
  
import javax.servlet.http.HttpServletRequest;  
import javax.servlet.http.HttpServletResponse;  
  
import com.google.mvc.web.servlet.HandlerAdapter;  
import com.google.mvc.web.servlet.ModelAndView;  
  
public class HttpRequestHandlerAdapter implements HandlerAdapter {  
  
    @Override  
    public long getLastModified(HttpServletRequest request, Object handler) {         
        return 0;  
    }  
  
    @Override  
    public ModelAndView handle(HttpServletRequest request, HttpServletResponse response, Object handler)  
            throws Exception {  
        ((HttpRequestHandler) handler).handleRequest(request, response);  
        return null;  
    }  
  
    @Override  
    public boolean supports(Object handler) {         
        return (handler instanceof HttpRequestHandler);  
    }  
}  

ViewResolver用于指定View的生成方式，我们先来看下AbstractView的定义

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package com.google.mvc.web.servlet.mvc;  
  
import java.util.Iterator;  
import java.util.Map;  
import java.util.Map.Entry;  
  
import javax.servlet.ServletRequest;  
import javax.servlet.http.HttpServletRequest;  
import javax.servlet.http.HttpServletResponse;  
  
import org.apache.log4j.Logger;  
  
import com.google.mvc.web.servlet.View;  
  
public abstract class AbstractView implements View {  
      
    private static final Logger LOGGER = Logger.getLogger(AbstractView.class);  
      
    public static final String INCLUDE_REQUEST_URI_ATTRIBUTE = "javax.servlet.include.request_uri";  
    public static final String FORWARD_REQUEST_URI_ATTRIBUTE = "javax.servlet.forward.request_uri";  
    public static final String FORWARD_CONTEXT_PATH_ATTRIBUTE = "javax.servlet.forward.context_path";  
    public static final String FORWARD_SERVLET_PATH_ATTRIBUTE = "javax.servlet.forward.servlet_path";  
    public static final String FORWARD_PATH_INFO_ATTRIBUTE = "javax.servlet.forward.path_info";  
    public static final String FORWARD_QUERY_STRING_ATTRIBUTE = "javax.servlet.forward.query_string";  
    public static final String DEFAULT_CONTENT_TYPE = "text/html;charset=ISO-8859-1";     
    private String contentType = DEFAULT_CONTENT_TYPE;    
    private boolean alwaysInclude = false;    
  
    @Override  
    public String getContentType() {          
        return contentType;  
    }     
      
    protected void exposeModelAsRequestAttributes(Map<String, Object> model, HttpServletRequest request){  
        Iterator<Entry<String, Object>> it = model.entrySet().iterator();  
        while (it.hasNext()) {  
            Entry<String, Object> entry = it.next();  
              
            String modelName = entry.getKey();  
            Object modelValue = entry.getValue();  
            if (modelValue != null) {  
                request.setAttribute(modelName, modelValue);  
                if (LOGGER.isDebugEnabled()) {  
                    LOGGER.debug("Added model object '" + modelName + "' of type [" + modelValue.getClass().getName() +  
                            "] to request in view with name '" + this + "'");  
                }  
            } else {  
                request.removeAttribute(modelName);  
                if (LOGGER.isDebugEnabled()) {  
                    LOGGER.debug("Removed model object '" + modelName + "' from request in view with name '"   
                            + this + "'");  
                }  
            }  
        }  
          
    }  
  
    protected boolean useInclude(HttpServletRequest request, HttpServletResponse response) {  
        return (this.alwaysInclude || request.getAttribute(INCLUDE_REQUEST_URI_ATTRIBUTE) != null || response  
                .isCommitted());  
    }  
      
    protected void exposeForwardRequestAttributes(HttpServletRequest request) {  
        exposeRequestAttributeIfNotPresent(request, FORWARD_REQUEST_URI_ATTRIBUTE, request.getRequestURI());  
        exposeRequestAttributeIfNotPresent(request, FORWARD_CONTEXT_PATH_ATTRIBUTE, request.getContextPath());  
        exposeRequestAttributeIfNotPresent(request, FORWARD_SERVLET_PATH_ATTRIBUTE, request.getServletPath());  
        exposeRequestAttributeIfNotPresent(request, FORWARD_PATH_INFO_ATTRIBUTE, request.getPathInfo());  
        exposeRequestAttributeIfNotPresent(request, FORWARD_QUERY_STRING_ATTRIBUTE, request.getQueryString());  
    }  
      
    private void exposeRequestAttributeIfNotPresent(ServletRequest request, String name, Object value) {  
        if (request.getAttribute(name) == null) {  
            request.setAttribute(name, value);  
        }  
    }  
  
    public void setContentType(String contentType) {  
        this.contentType = contentType;  
    }  
      
    public boolean isAlwaysInclude() {  
        return alwaysInclude;  
    }  
  
    public void setAlwaysInclude(boolean alwaysInclude) {  
        this.alwaysInclude = alwaysInclude;  
    }  
}  

在这里我们仅实现一种View类型，也就是对jsp页面的简单处理。

[java] view plaincopy



package com.google.mvc.web.servlet.mvc;  
  
import java.io.IOException;  
import java.util.Map;  
  
import javax.servlet.RequestDispatcher;  
import javax.servlet.ServletException;  
import javax.servlet.http.HttpServletRequest;  
import javax.servlet.http.HttpServletResponse;  
  
import org.apache.log4j.Logger;  
  
public class InternalResourceView extends AbstractView {  
  
    private static final Logger LOGGER = Logger.getLogger(InternalResourceView.class);  
    private String url;  
      
    @Override  
    public void render(Map<String, Object> model, HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {          
        if (LOGGER.isDebugEnabled()) {  
            LOGGER.debug("Rendering view with name '" + this + "' with model " + model);  
        }     
          
        if(model != null){  
            exposeModelAsRequestAttributes(model, request);       
        }  
          
        RequestDispatcher rd = request.getRequestDispatcher(url);  
        if (rd == null) {  
            throw new ServletException("Could not get RequestDispatcher for ["   
                    + getUrl() + "]: check that this file exists within your WAR");  
        }  
          
        if (useInclude(request, response)) {  
            response.setContentType(getContentType());  
            rd.include(request, response);  
            if (LOGGER.isDebugEnabled()) {  
                LOGGER.debug("Included resource [" + getUrl() + "] in InternalResourceView '" + url + "'");  
            }  
        }else {  
            exposeForwardRequestAttributes(request);  
            rd.forward(request, response);  
            if (LOGGER.isDebugEnabled()) {  
                LOGGER.debug("Forwarded to resource [" + getUrl() + "] in InternalResourceView '" + url + "'");  
            }  
        }         
    }     
      
    public String getUrl() {  
        return url;  
    }  
  
    public void setUrl(String url) {  
        this.url = url;  
    }  
      
    public String toString(){  
        return this.url;  
    }  
  
}  

好了，到这里，我们再来看看ViewResolver类的实现

[java] view plaincopy



package com.google.mvc.web.servlet.mvc;  
  
import org.apache.log4j.Logger;  
  
import com.google.mvc.web.servlet.View;  
import com.google.mvc.web.servlet.ViewResolver;  
  
public class DefaultViewResolver implements ViewResolver  
{  
    private static final Logger LOGGER = Logger.getLogger(DefaultViewResolver.class);  
    private String prefix = "";  
    private String suffix = "";  
    private Class<View> viewClass;  
  
    @Override  
    public View resolveViewName(String viewName) throws Exception {  
        View view = viewClass.newInstance();  
        if(view instanceof InternalResourceView){  
            ((InternalResourceView)view).setUrl(prefix + viewName + suffix);  
        }  
        return view;  
    }  
      
    public void setViewClass(String viewClass){  
        try {  
            this.viewClass = (Class<View>) this.getClass().getClassLoader().loadClass(viewClass);  
        } catch (ClassNotFoundException e) {              
            LOGGER.error("Can't load view class " + viewClass, e);  
        }  
    }  
  
    public String getPrefix() {  
        return prefix;  
    }  
  
    public void setPrefix(String prefix) {  
        this.prefix = prefix;  
    }  
  
    public String getSuffix() {  
        return suffix;  
    }  
  
    public void setSuffix(String suffix) {  
        this.suffix = suffix;  
    }  
}  

到这里，我们在整个MVC架构的源码实现已经完成了，下一篇，我们将介绍一个基于我们这个MVC架构的Demo。

文章来源：http://blog.****.net/zhiqiangzhan/article/details/4768172

MVC架构探究及其源码兑现(5)-相关组件实现

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