read appfuse-初始化-2

王朝java/jsp·作者佚名  2006-01-31
窄屏简体版  字體: |||超大  

应用程序启动时,调用StartupListener初始化ServletCOntext环境变量、Spring环境变量和取得角色信息后,接着执行UserCounterListener监听器。

★ UserCounterListener功能:计算使用应用的用户个数和存储用户对象。应用启动使初始化用户数变量counter,并存入ServletContext,利用HttpSessionAttributeListener监听器每当Session中的属性值有变化时,修改ServletContext中的用户个数和,用户对象。

提供了一种全局跟踪用户信息的方法。

UserCounterListener监听器实现比较简单,主要时理解ServletContextListener和HttpSessionAttributeListener监听器的使用。

★ web.xml

<listener>

<listener-class>org.dudu.webapp.listener.UserCounterListener</listener-class>

</listener>

★ UserCounterListener监听器程序:

UserCounterListener出来继承了ServletContextListener监听器接口外,还继承了

HttpSessionAttributeListener监听器接口。ServletContextListener监听器接口的作用已经在“初始化”前一部分作了介绍。

★ HttpSessionAttributeListener监听器介绍:HttpSessionAttributeListener监听

HttpSession中的属性的操作。当在Session增加一个属性时,激发

attributeAdded(HttpSessionBindingEvent se) 方法;当在Session删除一个属性时,激发

attributeRemoved(HttpSessionBindingEvent se)方法;当在Session属性被重新设置时,激

发attributeReplaced(HttpSessionBindingEvent se) 方法。

public class UserCounterListener implements ServletContextListener,

HttpSessionAttributeListener {

public static final String COUNT_KEY = "userCounter";

public static final String USERS_KEY = "userNames";

private final transient Log log = LogFactory.getLog(UserCounterListener.class);

private transient ServletContext servletContext;

private int counter;

private Set users;

public synchronized void contextInitialized(ServletContextEvent sce) {

servletContext = sce.getServletContext();

servletContext.setAttribute((COUNT_KEY), Integer.toString(counter));

}

public synchronized void contextDestroyed(ServletContextEvent event) {

servletContext = null;

users = null;

counter = 0;

}

synchronized void incrementUserCounter() {

counter =

Integer.parseInt((String) servletContext.getAttribute(COUNT_KEY));

counter++;

servletContext.setAttribute(COUNT_KEY, Integer.toString(counter));

if (log.isDebugEnabled()) {

log.debug("User Count: " + counter);

}

}

synchronized void decrementUserCounter() {

int counter =

Integer.parseInt((String) servletContext.getAttribute(COUNT_KEY));

counter--;

if (counter < 0) {

counter = 0;

}

servletContext.setAttribute(COUNT_KEY, Integer.toString(counter));

if (log.isDebugEnabled()) {

log.debug("User Count: " + counter);

}

}

synchronized void addUsername(Object user) {

users = (Set) servletContext.getAttribute(USERS_KEY);

if (users == null) {

users = new HashSet();

}

if (log.isDebugEnabled()) {

if (users.contains(user)) {

log.debug("User already logged in, adding anyway...");

}

}

users.add(user);

servletContext.setAttribute(USERS_KEY, users);

incrementUserCounter();

}

synchronized void removeUsername(Object user) {

users = (Set) servletContext.getAttribute(USERS_KEY);

if (users != null) {

users.remove(user);

}

servletContext.setAttribute(USERS_KEY, users);

decrementUserCounter();

}

public void attributeAdded(HttpSessionBindingEvent event) {

if (event.getName().equals(Constants.USER_KEY)) {

addUsername(event.getValue());

}

}

public void attributeRemoved(HttpSessionBindingEvent event) {

if (event.getName().equals(Constants.USER_KEY)) {

removeUsername(event.getValue());

}

}

public void attributeReplaced(HttpSessionBindingEvent event) {

// I don't really care if the user changes their information

}

}

 
 
 
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