一
1、启动一个WEB项目的时候，WEB容器会去读取它的配置文件web.xml，读取<listener>和<context-param>两个结点。<wbr></wbr>
2、紧急着，容创建一个ServletContext（servlet上下文），这个web项目的所有部分都将共享这个上下文。<wbr></wbr>
3、容器将<context-param>转换为键值对，并交给servletContext。<wbr></wbr>
4、容器创建<listener>中的类实例，创建监听器。<wbr></wbr>
二 <wbr>Load-on-startup</wbr>
Load-on-startup元素在web应用启动的时候指定了servlet被加载的顺序，它的值必须是一个整数。如果它的值是一个负整数或是这个元素不存在，那么容器会在该servlet被调用的时候，加载这个servlet。如果值是正整数或零，容器在配置的时候就加载并初始化这个servlet，容器必须保证值小的先被加载。如果值相等，容器可以自动选择先加载谁。<wbr></wbr>
在servlet的配置当中，<load-on-startup>5</load-on-startup>的含义是：<wbr></wbr>
标记容器是否在启动的时候就加载这个servlet。<wbr></wbr>
当值为0或者大于0时，表示容器在应用启动时就加载这个servlet；<wbr></wbr>
当是一个负数时或者没有指定时，则指示容器在该servlet被选择时才加载。<wbr></wbr>
正数的值越小，启动该servlet的优先级越高。<wbr></wbr>
三 <wbr>加载顺序</wbr>
首先可以肯定的是，加载顺序与它们在 web.xml 文件中的先后顺序无关。即不会因为 filter 写在 listener的前面而会先加载 filter。最终得出的结论是：ServletContext-><wbr>listener ->filter -> servlet</wbr>
<wbr><wbr><wbr><wbr><wbr>同时还存在着这样一种配置节：context-param，它用于向 ServletContext提供键值对，即应用程序上下文信息。我们的 listener, filter 等在初始化时会用到这些上下文中的信息，那么context-param 配置节是不是应该写在 listener 配置节前呢？实际上 context-param配置节可写在任意位置，因此真正的加载顺序为：context-param -> listener-> filter -> servlet</wbr></wbr></wbr></wbr></wbr>
<wbr><wbr><wbr><wbr><wbr>对于某类配置节而言，与它们出现的顺序是有关的。以filter 为例，web.xml 中当然可以定义多个 filter，与 filter 相关的一个配置节是filter-mapping，这里一定要注意，对于拥有相同 filter-name 的 filter 和 filter-mapping配置节而言，filter-mapping 必须出现在 filter 之后，否则当解析到 filter-mapping 时，它所对应的filter-name 还未定义。web 容器启动时初始化每个 filter 时，是按照 filter配置节出现的顺序来初始化的，当请求资源匹配多个 filter-mapping 时，filter 拦截资源是按照filter-mapping 配置节出现的顺序来依次调用 doFilter() 方法的。</wbr></wbr></wbr></wbr></wbr>
<wbr><wbr><wbr><wbr><wbr>servlet 同 filter类似，此处不再赘述。</wbr></wbr></wbr></wbr></wbr>
<wbr><wbr><wbr><wbr> 由此，可以看出，web.xml 的加载顺序是：ServletContext-><wbr>context-param ->listener -> filter -> servlet，而同个类型之间的实际程序调用的时候的顺序是根据对应的 mapping 的顺序进行调用的。</wbr></wbr></wbr></wbr></wbr>
<wbr></wbr>
四<wbr>web.xml文件详解<wbr></wbr></wbr>
<wbr></wbr>
我将自己知道的web.xml的元素整理了一下：
web.xml首先是肯定要包含它的schema.
<web-app xmlns="http://java.sun.com/xml/ns/j2ee"
<wbr><wbr><wbr>xmlns:xsi="<a href="http://www.w3.org/2001/XMLSchema-instance" style="text-decoration:none; color:rgb(0,107,173)">http://www.w3.org/2001/XMLSchema-instance</a>"<br><wbr><wbr><wbr>xsi:schemaLocation="<a href="http://java.sun.com/xml/ns/j2ee/web-app_2_4.xsd" style="text-decoration:none; color:rgb(0,107,173)">http://java.sun.com/xml/ns/j2ee/web-app_2_4.xsd</a>"<br><wbr><wbr><wbr>version="2.4"></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr>
</web-app>
其它的元素都放在<web-app></web-app>之中。
<discription></discription>是对站台的描述
<display-name></display-name>定义站台的名称
<distributable/> 是指定该站台是否可分布式处理
<context-param></context-param>用来设定web站台的环境参数，它包含两个子元素：
<wbr><wbr><wbr><param-name></param-name>用来指定参数的名称<br><wbr><wbr><wbr><param-value></param-value>用来设定参数值</wbr></wbr></wbr></wbr></wbr></wbr>
比如：
<context-param>
<wbr><wbr><wbr><param-name>my_param</param-name><br><wbr><wbr><wbr><param-value>hello</param-value><br> </context-param></wbr></wbr></wbr></wbr></wbr></wbr>
在此设定的参数，可以在servlet中用getServletContext().getInitParameter("my_param") 来取得
<filter></filter>是用来声明filter的相关设定，它包含以下子元素：
<wbr><wbr><wbr><filter-name></filter-name>这当然就是指定filter的名字<br><wbr><wbr><wbr><filter-class></filter-class>这是用来定义filter的类的名称<br><wbr><wbr><wbr><init-param></init-param>用来定义参数，它有两个子元素：<br><wbr><wbr><wbr><wbr><wbr><wbr><wbr><param-name></param-name>用来指定参数的名称<br><wbr><wbr><wbr><wbr><wbr><wbr><wbr><param-value></param-value>用来设定参数值</wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr>
比如：
<filter>
<wbr><wbr><wbr><wbr><wbr><wbr><wbr><filter-name>setCharacterEncoding</filter-name><br><wbr><wbr><wbr><wbr><wbr><wbr><wbr><filter-class>com.myTest.setCharacterEncodingFilt<wbr>er</filter-class><br><wbr><wbr><wbr><wbr><wbr><wbr><wbr><init-param><br><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><param-name>encoding</param-name><br><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><param-value>GB2312</param-value><br><wbr><wbr><wbr><wbr><wbr><wbr><wbr></init-param><br> </filter></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr>
与<filter></filter>同时使用的是<filter-mapping></filter-mapping>用来定义filter所对应的URL，它有两个子元素：
<wbr><wbr><wbr><filter-name></filter-name>指定filter的名字<br><wbr><wbr><wbr><url-pattern></url-pattern>指定filter所对应的URL</wbr></wbr></wbr></wbr></wbr></wbr>
比如：
<filter-mapping>
<wbr><wbr><wbr><wbr><wbr><wbr><wbr><filter-name>setCharacterEncoding</filter-name><br><wbr><wbr><wbr><wbr><wbr><wbr><wbr><url-pattern>/*</url-pattern><br> </filter-mapping></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr>
<listener></listener>用来设定Listener接口，它的主要子元素为
<wbr><wbr><wbr><listener-class></listener-class>定义Listener的类名称</wbr></wbr></wbr>
比如：
<listener>
<wbr><wbr><wbr><listener-class>com.myTest.ContextListener</listener-class><wbr><br> </listener></wbr></wbr></wbr></wbr>
<servlet></servlet>用来声明一个servlet的数据，主要有以下子元素：
<wbr><wbr><wbr><servlet-name></servlet-name>指定servlet的名称<br><wbr><wbr><wbr><servlet-class></servlet-class>指定servlet的类名称</wbr></wbr></wbr></wbr></wbr></wbr>
<wbr><wbr><wbr><jsp-file></jsp-file>指定web站台中的某个JSP网页的完整路径<br><wbr><wbr><wbr><init-param></init-param>用来定义参数，和前面的<init-param>差不多</wbr></wbr></wbr></wbr></wbr></wbr>
同样，与<servlet></servlet>一起使用的是<servlet-mapping></servlet-mapping>用来定义servlet所对应的URL，包含两个子元素：
<wbr><wbr><wbr><servlet-name></servlet-name>指定servlet的名称<br><wbr><wbr><wbr><url-pattern></url-pattern>指定servlet所对应的URL</wbr></wbr></wbr></wbr></wbr></wbr>
比如：
<servlet>
<wbr><wbr><wbr><wbr><wbr><wbr><wbr><servlet-name>ShoppingServlet</servlet-name><br><wbr><wbr><wbr><wbr><wbr><wbr><wbr><servlet-class>com.myTest.ShoppingServlet</servlet-class><br> </servlet><br><wbr><wbr><wbr><wbr><br> <servlet-mapping><br><wbr><wbr><wbr><wbr><wbr><wbr><wbr><servlet-name>ShoppingServlet</servlet-name><br><wbr><wbr><wbr><wbr><wbr><wbr><wbr><url-pattern>/shop/ShoppingServlet</url-pattern><br> </servlet-mapping></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr>
<session-config></session-config>用来定义web站台中的session参数，包含一个子元素：
<wbr><wbr><wbr><session-timeout></session-timeout>用来定义这个web站台所有session的有效期限，单位为<wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr>分钟</wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr>
<mime-mapping></mime-mapping>定义某一个扩展名和某一个MIMEType做对映，包含两个<wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr>子元素：<br><wbr><wbr><wbr><extension></extension>扩展名的名称<br><wbr><wbr><wbr><mime-type></mime-type>MIME格式</wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr>
比如：
<mime-mapping>
<wbr><wbr><wbr><extension>doc</extension><br><wbr><wbr><wbr><mime-type>application/vnd.ms-word</mime-type><br> </mime-mapping><wbr><br> <mime-mapping><br><wbr><wbr><wbr><extension>xls</extension><br><wbr><wbr><wbr><mime-type>application/vnd.ms-excel</mime-type><br> </mime-mapping></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr>
<welcome-file-list></welcom-file-list>用来定义首页的列单，包含一个子元素：
<wbr><wbr><wbr><welcome-file></welcome-file>指定首页的文件名称</wbr></wbr></wbr>
比如：
<welcome-file-list>
<wbr><wbr><wbr><welcome-file>index.jsp</welcome-file><br><wbr><wbr><wbr><welcome-file>index.html</welcome-file><br> </welcom-file-list></wbr></wbr></wbr></wbr></wbr></wbr>
<error-page></error-page>用来处理错误代码或异常的页面，有三个子元素：
<wbr><wbr><wbr><error-code></error-code>指定错误代码<br><wbr><wbr><wbr><exception-type></exception-type>指定一个JAVA异常类型<br><wbr><wbr><wbr><location></location>指定在web站台内的相关资源路径</wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr>
比如：
<error-page>
<wbr><wbr><wbr><error-code>404</error-code><br><wbr><wbr><wbr><location>/error404.jsp</location><br> </error-page><br> <error-page><br><wbr><wbr><wbr><exception-type>java.lang.Exception</exception-type><br><wbr><wbr><wbr><location>/exception.jsp</location><br> </error-page></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr>
<taglib></taglib>用来设定JSP网页所用到的Tag Library路径，有两个子元素：
<wbr><wbr><wbr><taglib-uri></taglib-uri>定义TLD文件的URI，在JSP网页中用taglib指令便可取得该URI的<wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr>TLD文件<br><wbr><wbr><wbr><taglib-location></taglib-location>指定TLD文件相对于web站台的存放位置</wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr>
比如：
<taglib>
<wbr><wbr><wbr><wbr><wbr><taglib-uri>myTaglib</taglib-uri><br><wbr><wbr><wbr><wbr><wbr><taglib-location>/WEB-INF/tlds/MyTaglib.tld</taglib-location><br> </taglib></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr>
<resource-ref></resource-ref>定义利用JNDI取得站台可利用的资源，有五个子元素：
<wbr><wbr><wbr><description></description>资源说明<br><wbr><wbr><wbr><rec-ref-name></rec-ref-name>资源名称<br><wbr><wbr><wbr><res-type></res-type>资源种类<br><wbr><wbr><wbr><res-auth></res-auth>资源经由Application或Container来许可<br><wbr><wbr><wbr><res-sharing-scope></res-sharing-scope>资源是否可以共享，有Shareable和Unshareable两个<wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr>值，默认为Shareable</wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr>
比如，配置数据库连接池就可在此配置：
<resource-ref>
<wbr><wbr><wbr><wbr><wbr><wbr><wbr><description>JNDI JDBC DataSource ofshop</description><br><wbr><wbr><wbr><wbr><wbr><wbr><wbr><res-ref-name>jdbc/sample_db</res-ref-name><br><wbr><wbr><wbr><wbr><wbr><wbr><wbr><res-type>javax.sql.DataSource</res-type><br><wbr><wbr><wbr><wbr><wbr><wbr><wbr><res-auth>Container</res-auth><br> </resource-ref></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr>
<jsp-config>包括<taglib>和<jsp-property-group> 两个子元素。
<wbr><wbr><wbr><wbr><br><wbr><wbr><wbr>其中<taglib>元素在JSP1.2时就已经存在；而<jsp-property-group>是JSP2.0 新增的元素。<br><wbr><wbr><wbr><jsp-property-group>元素主要有八个子元素，它们分别为：<br><wbr><wbr><wbr><wbr><br><wbr><wbr><wbr>1.<description>：设定的说明；<br><wbr><wbr><wbr>2.<display-name>：设定名称；<br><wbr><wbr><wbr>3.<url-pattern>：设定值所影响的范围，如：/CH2 或/*.jsp；<br><wbr><wbr><wbr>4.<el-ignored>：若为true，表示不支持EL语法；<br><wbr><wbr><wbr>5.<scripting-invalid>：若为true，表示不支持<%scripting %>语法；<br><wbr><wbr><wbr>6.<page-encoding>：设定JSP 网页的编码；<br><wbr><wbr><wbr>7.<include-prelude>：设置JSP网页的抬头，扩展名为.jspf；<br><wbr><wbr><wbr>8.<include-coda>：设置JSP网页的结尾，扩展名为.jspf。</wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr>
一个简单的<jsp-config>元素完整配置：
<jsp-config>
<wbr><wbr><wbr><taglib><br><wbr><wbr><wbr><wbr><wbr><wbr><wbr><taglib-uri>Taglib</taglib-uri><br><wbr><wbr><wbr><wbr><wbr><wbr><wbr><taglib-location>/WEB-INF/tlds/MyTaglib.tld</taglib-location><br><wbr><wbr><wbr></taglib><br><wbr><wbr><wbr><jsp-property-group><br><wbr><wbr><wbr><wbr><wbr><wbr><wbr><description>Special property groupfor JSP Configuration JSPexample.</description><br><wbr><wbr><wbr><wbr><wbr><wbr><wbr><display-name>JSPConfiguration</display-name><br><wbr><wbr><wbr><wbr><wbr><wbr><wbr><url-pattern>/jsp/*</url-pattern><br><wbr><wbr><wbr><wbr><wbr><wbr><wbr><el-ignored>true</el-ignored><br><wbr><wbr><wbr><wbr><wbr><wbr><wbr><page-encoding>GB2312</page-encoding><br><wbr><wbr><wbr><wbr><wbr><wbr><wbr><scripting-invalid>true</scripting-invalid><br><wbr><wbr><wbr><wbr><wbr><wbr><wbr><include-prelude>/include/prelude.jspf</include-prelude><br><wbr><wbr><wbr><wbr><wbr><wbr><wbr><include-coda>/include/coda.jspf</include-coda><br><wbr><wbr><wbr></jsp-property-group><br> </jsp-config><wbr><wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr>
配置web.xml来限制对某些servlet的请求
有时我们只希望通过认证的用户才能请求某些servlet的话，就可以在web.xml中来进行相应的配置，来达到此目的。
这就要用到<security-constraint></security-constraint>元素。
对于tomcat，中web.xml使用security-constraint元素需要在位于<Tomcat-installation-directory>/conf/tomcat-users.xml的XML文件中创建用户名和密码。比如下面的这个tomcat-users.xml文件：
<?xml version='1.0'encoding='utf-8'?>
<tomcat-users>
<wbr> <rolerolename="tomcat"/><br><wbr> <rolerolename="manager"/><br><wbr> <rolerolename="admin"/><br><wbr> <user username="tomcat"password="tomcat" roles="tomcat"/><br><wbr> <user username="both"password="tomcat" roles="tomcat,manager"/><br><wbr> <user username="admin"password="admin" roles="admin"/><br> </tomcat-users></wbr></wbr></wbr></wbr></wbr></wbr>
此XML片段包括一个tomcat-users根元素，它包含一个或多个role和user元素。
然后在Web应用程序的web.xml中创建security-constraint、login-config和security-role元素。
<security-constraint>
<wbr><wbr><wbr><wbr><wbr><web-resource-collection><br><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><web-resource-name>HelloServlet</web-resource-name><br><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><url-pattern>/HelloServlet</url-pattern><br><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><http-method>GET</http-method><br><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><http-method>POST</http-method><br><wbr><wbr><wbr><wbr><wbr></web-resource-collection><br><wbr><wbr><wbr><wbr><wbr><auth-constraint><br><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><description>This applies only to the"tomcat" securityrole</description><br><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><role-name>admin</role-name><br><wbr><wbr><wbr><wbr><wbr></auth-constraint><br><wbr><wbr><wbr><wbr><wbr><user-data-constraint><br><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><transport-guarantee>NONE</transport-guarantee><br><wbr><wbr><wbr><wbr><wbr></user-data-constraint><br><wbr></security-constraint><br><wbr><wbr><br><wbr><login-config><br><wbr><wbr><wbr><wbr><wbr><auth-method>BASIC</auth-method><br><wbr></login-config><br><wbr><security-role><br><wbr><wbr><wbr><wbr><wbr><role-name>admin</role-name><br><wbr></security-role></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr>
其中security-constraint元素包含一个或多个web-resource-collection元素，它是描述Web应用程序中的哪些web资源受到指定安全限制的保护。http-method元素指定安全限制覆盖的HTTP方法。上面的例子中，当我们对/HelloServlet的GET或POST请求时将触发配置的安全机制。
auth-constraint元素用于描述允许访问Web组件的安全角色。此例中安全角色的例子有tomcat、manager、admin。而只有当作为admin角色的用户才可以访问HelloServlet。
Web应用程序通过login-config元素来认证用户，并确认该用户是否为正确的角色。
longin-config包含的transport-guarantee子元素用来指定认证方法，BASIC是一种常见的Web认证方式，浏览器给用户提示一个对话框，要求输入用户名和密码，随后Tomcat将给出的用户名和密码与tomcat-users.xml中的用户名和密码进行比较，然后使用前面的security-constraint配置来确定用户是否可访问受保护的servlet。
（除BASIC外，还可以是FORM、CLIENT-CERT、DIGEST等）
其实这种认证方法实际上有两个步骤：
1、检查提供的用户名和密码是否正确。
2、判断用户是否映射到特定的安全角色。例如，用户可能提供了正确的用户名和密码，但没有映射到特定的安全角色，也将被禁止访问特定的Web资源。
五相应元素配置<wbr><wbr><wbr><wbr></wbr></wbr></wbr></wbr>
1、Web应用图标：指出IDE和GUI工具用来表示Web应用的大图标和小图标<wbr><wbr><wbr><wbr><br> <icon><wbr><wbr><wbr><wbr><br> <small-icon>/images/app_small.gif</small-icon><wbr><wbr><wbr><wbr><br> <large-icon>/images/app_large.gif</large-icon><wbr><wbr><wbr><wbr><br> </icon><wbr><wbr><wbr><wbr><br> 2、Web应用名称：提供GUI工具可能会用来标记这个特定的Web应用的一个名称<wbr><wbr><wbr><wbr><br> <display-name>TomcatExample</display-name><wbr><wbr><wbr><wbr><br> 3、Web 应用描述：给出于此相关的说明性文本<wbr><wbr><wbr><wbr><br> <disciption>Tomcat Example servletsand JSPpages.</disciption><wbr><wbr><wbr><wbr><br> 4、上下文参数：声明应用范围内的初始化参数。<wbr><wbr><wbr><wbr><br> <context-param><wbr><wbr><wbr><wbr><br><wbr><wbr><wbr><param-name>ContextParameter</para-name><wbr><wbr><wbr><wbr><br><wbr><wbr><wbr><param-value>test</param-value><wbr><wbr><wbr><wbr><br><wbr><wbr><wbr><description>It is a testparameter.</description><wbr><wbr><wbr><wbr><br> </context-param><wbr><wbr><wbr><wbr><br> 在servlet里面可以通过getServletContext().getInitParameter("context/param")得到<wbr><wbr><wbr><wbr><br><br> 5、过滤器配置：将一个名字与一个实现javaxs.servlet.Filter接口的类相关联。<wbr><wbr><wbr><wbr><br> <filter><wbr><wbr><wbr><wbr><br><wbr><wbr><wbr><wbr><wbr><wbr><wbr><filter-name>setCharacterEncoding</filter-name><wbr><wbr><wbr><wbr><br><wbr><wbr><wbr><wbr><wbr><wbr><wbr><filter-class>com.myTest.setCharacterEncodingFilt<wbr>er</filter-class><wbr><wbr><wbr><wbr><br><wbr><wbr><wbr><wbr><wbr><wbr><wbr><init-param><wbr><wbr><wbr><wbr><br><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><param-name>encoding</param-name><wbr><wbr><wbr><wbr><br><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><param-value>GB2312</param-value><wbr><wbr><wbr><wbr><br><wbr><wbr><wbr><wbr><wbr><wbr><wbr></init-param><wbr><wbr><wbr><wbr><br> </filter><wbr><wbr><wbr><wbr><br> <filter-mapping><wbr><wbr><wbr><wbr><br><wbr><wbr><wbr><wbr><wbr><wbr><wbr><filter-name>setCharacterEncoding</filter-name><wbr><wbr><wbr><wbr><br><wbr><wbr><wbr><wbr><wbr><wbr><wbr><url-pattern>/*</url-pattern><wbr><wbr><wbr><wbr><br> </filter-mapping><wbr><wbr><wbr><wbr><br> 6、监听器配置<wbr><wbr><wbr><wbr><br> <listener><wbr><wbr><wbr><wbr><br><wbr><wbr><wbr><wbr><wbr><listerner-class>listener.SessionListener</listener-class><wbr><wbr><wbr><wbr><br> </listener><wbr><wbr><wbr><wbr><br> 7、Servlet配置<wbr><wbr><wbr><wbr><br><wbr><wbr>基本配置<wbr><wbr><wbr><wbr><br><wbr><wbr><servlet><wbr><wbr><wbr><wbr><br><wbr><wbr><wbr><wbr><wbr><servlet-name>snoop</servlet-name><wbr><wbr><wbr><wbr><br><wbr><wbr><wbr><wbr><wbr><servlet-class>SnoopServlet</servlet-class><wbr><wbr><wbr><wbr><br><wbr><wbr></servlet><wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr>
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