我已经创建了 Web 应用程序,我想知道我应该将侦听器放在 web.xml 中的哪里。
<servlet>
<servlet-name>ProcessReg</servlet-name>
<servlet-class>ProcessReg</servlet-class>
<init-param>
<param-name>pract123</param-name>
<param-value>jdbc:odbc:practODBC</param-value>
</init-param>
<listener>
<listener-class>config</listener-class>
</listener>
</servlet>
我收到的错误消息是:
cvc-complex-type.2.4.a: Invalid content was found starting with element 'listener'. One of '{"http://java.sun.com/xml/ns/javaee":init-param, "http://java.sun.com/xml/ns/javaee":load-on-startup, "http://java.sun.com/xml/ns/javaee":run-as, "http://java.sun.com/xml/ns/javaee":security-role-ref}' is expected. [17]
这是我的配置文件:
public class config implements ServletContextListener {
private static final String ATTRIBUTE_NAME = "config";
private DataSource dataSource;
@Override
public void contextInitialized(ServletContextEvent event) {
ServletContext servletContext = event.getServletContext();
String databaseName = servletContext.getInitParameter("pract123");
try {
dataSource = (DataSource) new InitialContext().lookup("java:/comp /env/jdbc/TestDB");
} catch (NamingException e) {
throw new RuntimeException("Config failed: datasource not found", e);
}}
@Override
public void contextDestroyed(ServletContextEvent event) {
// NOOP.
}
public DataSource getDataSource() {
return dataSource;
}
public static config getInstance(ServletContext servletContext) {
return (config) servletContext.getAttribute(ATTRIBUTE_NAME);
}
}
您所做的是混淆了
<servlet>
和 <listener>
标签。他们应该分开。
应该是这样
<servlet>
<servlet-name>ProcessReg</servlet-name>
<servlet-class>ProcessReg</servlet-class>
<init-param>
<param-name>pract123</param-name>
<param-value>jdbc:odbc:practODBC</param-value>
</init-param>
</servlet>
<listener>
<listener-class>fully.qaulified.path.ContextListener</listener-class>
</listener>
或
<listener>
<listener-class>fully.qaulified.path.ContextListener</listener-class>
</listener>
<servlet>
<servlet-name>ProcessReg</servlet-name>
<servlet-class>ProcessReg</servlet-class>
<init-param>
<param-name>pract123</param-name>
<param-value>jdbc:odbc:practODBC</param-value>
</init-param>
</servlet>
在你的课堂上
package fully.qaulified.path;
public class ContextListener implements ServletContextListener {
..
..
旁注:
在Java中,类名以大写字母开头。
public class config
应该是
public class Config
Listener 标签应该定义在 web-app 标签下。
<web-app>
<display-name>MyListeningApplication</display-name>
<listener>
<listener-class>config</listener-class>
</listener>
<servlet-name>ProcessReg</servlet-name>
<servlet-class>ProcessReg</servlet-class>
<init-param>
<param-name>pract123</param-name>
<param-value>jdbc:odbc:practODBC</param-value>
</init-param>
</web-app>
监听器不应位于
servlet
标签内并提供完全限定名称
<listener>
<listener-class>com.somePackage.ListenerClass</listener-class>
</listener>
正如您在 wep-app 的内容模型中看到的:
Content Model : (((description*, display-name*, icon*)) | distributable | context-param | filter | filter-mapping |
listener | servlet | servlet-mapping | session-config | mime-mapping | welcome-file-list | error-page | jsp-config |
security-constraint | login-config | security-role | ((env-entry*, ejb-ref*, ejb-local-ref*, ((service-ref*)), resource-
ref*, resource-env-ref*, message-destination-ref*, persistence-context-ref*, persistence-unit-ref*, post-
construct*, pre-destroy*)) | message-destination | locale-encoding-mapping-list)*
它是
servlet
的兄弟姐妹,而不是孩子:
<servlet>
<servlet-name>ProcessReg</servlet-name>
<servlet-class>ProcessReg</servlet-class>
<init-param>
<param-name>pract123</param-name>
<param-value>jdbc:odbc:practODBC</param-value>
</init-param>
</servlet>
<listener>
<listener-class>config</listener-class>
</listener>
web.xml 是
<listener>
<listener-class>com.my.ServletContextClass</listener-class>
</listener>
<context-param>
<param-name>pract123</param-name>
<param-value>jdbc:odbc:practODBC</param-value>
</context-param>
com.my.ServletContextClass.java 是
public class ServletContextClass implements ServletContextListener {
public void contextInitialized(ServletContextEvent sce) {
ServletContext context = sce.getServletContext();
String value = context.getInitParameter("pract123");
System.out.println("value: " + value);
}
}
享受编码的乐趣:)