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。

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

1. 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

   package com.google.mvc.web.servlet.mvc;
   
   import javax.servlet.http.HttpServletRequest;
   import javax.servlet.http.HttpServletResponse;
   
   import com.google.mvc.web.servlet.ModelAndView;
   
   public interface Controller {
   
       ModelAndView handleRequest(HttpServletRequest request, HttpServletResponse response) throws Exception;
   }

2. HttpRequestHandler：用于处理简单的HTTP请求。接口定义如下

   package com.google.mvc.web.servlet.mvc;
   
   import javax.servlet.http.HttpServletRequest;
   import javax.servlet.http.HttpServletResponse;
   
   
   public interface HttpRequestHandler {
   
       void handleRequest(HttpServletRequest request, HttpServletResponse response) throws Exception;
   
   }

   我们来看一下HandlerFor404的简单实现。

   package com.google.mvc.web.servlet.mvc;
   
   import javax.servlet.http.HttpServletRequest;
   import javax.servlet.http.HttpServletResponse;
   
   public class HandlerFor404 implements HttpRequestHandler {
   
       @Override
       public void handleRequest(HttpServletRequest request, HttpServletResponse response) throws Exception {
           response.sendRedirect("404.html");
       }
   
   }

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

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

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

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。

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

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.csdn.net/zhiqiangzhan/article/details/4768172