1.DispacherServlet是前端控制器（Struts是Filter），负责接收前端请求，并根据请求找到具体的Handler（目前的Handler是方法级别的）；SpringMVC中DispacherServlet初始化放在web.xml中，<load-on-start>1</load-on-start>，意思是Servlet容器启动时自动加载该Servlet。
2.HandlerMapping：负责将URL和controller匹配到一起，简单来说就是根据URL找到具体的类（根据注解@Controller和@RequestMapping找到）；
3.HandlerAdapter：根据URL找到具体类的具体方法；
jdk 具体执行过程如下：
1.DispatcherServlet本质上还是一个Servlet，故需要在web容器里初始化
/**
* Initialize the strategy objects that this servlet uses.
* <p>May be overridden in subclasses in order to initialize further strategy objects.
*/
protected void initStrategies(ApplicationContext context) {
initMultipartResolver(context);
initLocaleResolver(context);
initThemeResolver(context);
initHandlerMappings(context); // 从ApplicationContext容器中初始生成HandlerMappings
initHandlerAdapters(context); // 初始化HandlerAdapter
initHandlerExceptionResolvers(context);
initRequestToViewNameTranslator(context);
initViewResolvers(context);
initFlashMapManager(context);
}
2.当有一个请求到达时，调用DispatcherServlet的doDispatch（）方法，该方法找到真正的handler处理该请求；主要代码如下：
/**
* Process the actual dispatching to the handler.
* <p>The handler will be obtained by applying the servlet‘s HandlerMappings in order.
* The HandlerAdapter will be obtained by querying the servlet‘s installed HandlerAdapters
* to find the first that supports the handler class.
* <p>All HTTP methods are handled by this method. It‘s up to HandlerAdapters or handlers
* themselves to decide which methods are acceptable.
* @param request current HTTP request
* @param response current HTTP response
* @throws Exception in case of any kind of processing failure
* 通过查找HandlerMapping找到真正的Handler；先找到handler class，根据该class找到HandlerAdapter； 通过查询servlet已注册的HandlerAdapters，找到真正处理该请求的method
*/
protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception {
HttpServletRequest processedRequest = request;
HandlerExecutionChain mappedHandler = null;
boolean multipartRequestParsed = false;
ModelAndView mv = null;
// Determine handler for the current request.返回HandlerExecutionChain；
mappedHandler = getHandler(processedRequest, false);
// Determine handler adapter for the current request.根据HandlerExecutionChain找到HandlerAdapter
HandlerAdapter ha = getHandlerAdapter(mappedHandler.getHandler());
// Actually invoke the handler.使用给定的handler处理请求；
mv = ha.handle(processedRequest, response, mappedHandler.getHandler());
}
protected HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception {
for (HandlerMapping hm : this.handlerMappings) {
if (logger.isTraceEnabled()) {
logger.trace(
"Testing handler map [" + hm + "] in DispatcherServlet with name ‘" + getServletName() + "‘");
}
//查询所有已注册的HandlerMapping beans找到处理该请求的Handler；
HandlerExecutionChain handler = hm.getHandler(request);
if (handler != null) {
return handler;
}
}
return null;
}
其中HandlerExecutionChain是有一个HandlerAdapter和若干个HandlerInteceptor组成，请求先经HandlerInteceptor处理后在传给Adapter。一般我们使用HandlerInteceptor做一些登录验证，安全验证等 3.HandlerInterceptor和Servlet里的Filter作用很像，下面讲一下关于Filter的东西
3.1 Filter作用？
用于HttpServletRequest预处理和HttpServletResponse后处理；执行流程是 request---->listener----->filter------>struts拦截器（？）----->Servlet，这是链式处理过程，请求最后总会到达Servlet的；
3.2 一般用来干啥？
用户登录验证，用户发来请求，拦截请求后，验证用户是否登录过，如果没有登录调到登录页面；日志功能；编码格式
3.3Filter有三个过程
Filter一般在服务器端工作，故web容器调用它的init（），在web容器初始化的时候创建Filter的实例对象；
chain.doFilter（），把要做的事情都放在doFilter（）方法里面完成；
3.4 filter使用配置文件注册，在web应用程序一启动，web服务器就会实例化filter对象；
filter实例化
web.xml配置：
<!-- 编码过滤器 -->
<filter>
<filter-name>setCharacterEncoding</filter-name>
<filter-class>com.company.strutstudy.web.servletstudy.filter.EncodingFilter</filter-class> //该过滤器（EncodingFilter）具体位置。
<init-param>
<param-name>encoding</param-name> // 设定encoding编码为utf-8.
<param-value>utf-8</param-value>
</init-param>
</filter>
<filter-mapping>
<filter-name>setCharacterEncoding</filter-name>
<url-pattern>/*</url-pattern> //处理所有页面的编码格式
</filter-mapping>
<!-- 请求url日志记录过滤器 -->
<filter>
<filter-name>logfilter</filter-name>
<filter-class>com.company.strutstudy.web.servletstudy.filter.LogFilter</filter-class>
</filter>
<filter-mapping>
<filter-name>logfilter</filter-name>
<url-pattern>/*</url-pattern>
</filter-mapping>
编码拦截器：
public class EncodingFilter implements Filter {
private String encoding;
private Map<String, String> params = new HashMap<String, String>();
// 项目结束时就已经进行销毁
public void destroy() {
System.out.println("end do the encoding filter!");
params=null;
encoding=null;
}
public void doFilter(ServletRequest req, ServletResponse resp,
FilterChain chain) throws IOException, ServletException {
//UtilTimerStack.push("EncodingFilter_doFilter:");
System.out.println("before encoding " + encoding + " filter！");
req.setCharacterEncoding(encoding);
// resp.setCharacterEncoding(encoding);
// resp.setContentType("text/html;charset="+encoding);
chain.doFilter(req, resp);
System.out.println("after encoding " + encoding + " filter！");
System.err.println("----------------------------------------");
//UtilTimerStack.pop("EncodingFilter_doFilter:");
}
// 项目启动时就已经进行读取
public void init(FilterConfig config) throws ServletException {
System.out.println("begin do the encoding filter!");
encoding = config.getInitParameter("encoding");
for (Enumeration e = config.getInitParameterNames(); e
.hasMoreElements();) {
String name = (String) e.nextElement();
String value = config.getInitParameter(name);
params.put(name, value);
}
}
}
时间： 2024-08-30 09:27:07