Listener (Servlet 七)

※HttpSessionBindingListener

Servlet的內鍵觸發程式，也就是做了什麼事後，會自動做某件事
可以想成javascript的onXXX，譬如onClick，當使用者按一下滑鼠後，會自動做某件事
這裡的Binding是挷setAttribute(還要呼叫建構子)和removeAttribute

public class TestListener implements HttpSessionBindingListener {
    PrintWriter out;
    
    public TestListener(PrintWriter out){
        this.out = out;
    }
    
    @Override
    public void valueBound(HttpSessionBindingEvent e) {
        out.println("valueBound");
        out.println(e.getName());
        out.println(e.getValue());
    }
    
    @Override
    public void valueUnbound(HttpSessionBindingEvent e) {
        out.println("valueUnbound");
        out.println(e.getName());
        out.println(e.getValue());
    }
}

※寫一支class，實作HttpSessionBindingListener讓session觸發

resp.setContentType("text/plain");
req.getSession().setAttribute("out", new TestListener(resp.getWriter()));

※在doXXX加入這兩行就會觸發

※第一行不打也可以，只是不會換行，會變成空格，所以不寫的話也可以改成在listener那一支加<br />

※觸發的是valueBound，如果想觸發valueUnbound，就按一下重整或上一頁再下一頁，就會看到了，所以valueUnbound在reload、重整、呼叫removeAttribute、contain的預設30分session失效都會觸發

※ServletContextListener

container啟動和關閉時會觸發的listener

@WebListener
@WebInitParam(name = "p1", value = "ppp")
public class TestListener implements ServletContextListener {
// PrintWriter out;
//
// public TestListener(PrintWriter out) {
// this.out = out;
// }
    
    @Override
    public void contextInitialized(ServletContextEvent e) {
        System.out.println("contextInitialized");
        ServletContext sc = e.getServletContext();
        System.out.println(sc.getContextPath());
        System.out.println(sc.getInitParameter("p1"));
        System.out.println(sc.getInitParameter("abc"));
        System.out.println(sc.getInitParameter("def"));
    }
    
    @Override
    public void contextDestroyed(ServletContextEvent e) {
        System.out.println("contextDestroyed");
    }
}

※如果將out註解打開，程式無法啟動，會出現兩個錯誤
InstantiationException: listener.TestListener
NoSuchMethodException: listener.TestListener.<init>()
程式才剛啟動，當然是抓不到了

※這是annotation寫法，@WebListener有一個參數，是描述，很少人在寫

※@WebInitParam沒有作用，要設定初始參數只能寫在web.xml了

<listener>
    <listener-class>listener.TestListener</listener-class>
</listener>
    
<context-param>
    <param-name>abc</param-name>
    <param-value>111</param-value>
</context-param>
    
<context-param>
    <param-name>def</param-name>
    <param-value>222</param-value>
</context-param>

※listener包住listener-class，等同@WebListener，擇一使用

※在reload和關閉container時，會觸發contextDestroyed方法，注意和之前一樣，要按Servers的紅鈕，按Console的紅鈕和按右上角的X是不會執行到contextDestroyed方法的

※ServletContextAttributeListener

ServletContext在新增、取代、移除屬性時觸發

@WebListener
public class TestListener implements ServletContextAttributeListener {
    @Override
    public void attributeAdded(ServletContextAttributeEvent e) {
        System.out.println("attributeAdded");
        System.out.println(e.getName());
        System.out.println(e.getValue());
        System.out.println(e.getServletContext());
    }
    
    @Override
    public void attributeRemoved(ServletContextAttributeEvent e) {
        System.out.println("attributeRemoved");
        System.out.println(e.getName());
        System.out.println(e.getValue());
        System.out.println(e.getServletContext());
    }
    
    @Override
    public void attributeReplaced(ServletContextAttributeEvent e) {
        System.out.println("attributeReplaced");
        System.out.println(e.getName());
        System.out.println(e.getValue());
        System.out.println(e.getServletContext());
    }
}

※比較奇怪的是，我一run到jsp頁面，就會觸發added了，如下訊息：
attributeAdded
org.apache.jasper.runtime.JspApplicationContextImpl
org.apache.jasper.runtime.JspApplicationContextImpl@6f1943a6
org.apache.catalina.core.ApplicationContextFacade@4373821f

※測試

resp.setContentType("text/plain");
ServletContext sc = req.getServletContext();
sc.setAttribute("k", "v");
sc.setAttribute("k", "v");
sc.removeAttribute("k");

※取代時，就算value一樣也能觸發；移除時，一定要有key被移除才會觸發

※HttpSessionAttributeListener

HttpSession在新增、取代、移除屬性時觸發

@WebListener
public class TestListener implements HttpSessionAttributeListener {
    @Override
    public void attributeAdded(HttpSessionBindingEvent e) {
        System.out.println("attributeAdded");
        System.out.println(e.getName());
        System.out.println(e.getValue());
        System.out.println(e.getSession().getId());
    }
    
    @Override
    public void attributeRemoved(HttpSessionBindingEvent e) {
        System.out.println("attributeRemoved");
        System.out.println(e.getName());
        System.out.println(e.getValue());
        System.out.println(e.getSession().getId());
    }
    
    @Override
    public void attributeReplaced(HttpSessionBindingEvent e) {
        System.out.println("attributeReplaced");
        System.out.println(e.getName());
        System.out.println(e.getValue());
        System.out.println(e.getSession().getId());
    }
}

※因為是HttpSession，所以沒有getServletContext方法了

※測試

resp.setContentType("text/plain");
HttpSession session = req.getSession();
session.setAttribute("k", "v");
session.setAttribute("k", "v");
session.removeAttribute("x");

※和ServletContextAttributeListener一樣，但執行頁面時不會觸發

※HttpSessionListener

@WebListener
public class TestListener implements HttpSessionListener {
    @Override
    public void sessionCreated(HttpSessionEvent e) {
        System.out.println("sessionCreated");
        System.out.println(e.getSession().getId());
    }
    
    @Override
    public void sessionDestroyed(HttpSessionEvent e) {
        System.out.println("sessionDestroyed");
        System.out.println(e.getSession().getId());
    }
}

※測試

HttpSession session = req.getSession();
session.invalidate();

HttpSessionActivationListener參考良葛格的網站，總之就是JVM搬到另一個JVM的觸發程式

※ServletRequestListener、ServletRequestAttributeListener

@WebListener
public class TestListener implements ServletRequestListener, ServletRequestAttributeListener {
    @Override
    public void requestDestroyed(ServletRequestEvent e) {
        System.out.println("requestDestroyed");
        System.out.println(e.getServletContext().getServletContextName());
        System.out.println(e.getServletRequest().getLocalName());
    }
    
    @Override
    public void requestInitialized(ServletRequestEvent e) {
        System.out.println("requestInitialized");
        System.out.println(e.getServletContext().getServletContextName());
        System.out.println(e.getServletRequest().getLocalName());
    }
    
    @Override
    public void attributeAdded(ServletRequestAttributeEvent e) {
        System.out.println("attributeAdded");
        System.out.println(e.getName());
        System.out.println(e.getValue());
    }
    
    @Override
    public void attributeRemoved(ServletRequestAttributeEvent e) {
        System.out.println("attributeRemoved");
        System.out.println(e.getName());
        System.out.println(e.getValue());
    }
    
    @Override
    public void attributeReplaced(ServletRequestAttributeEvent e) {
        System.out.println("attributeReplaced");
        System.out.println(e.getName());
        System.out.println(e.getValue());
    }
}

※測試

resp.setContentType("text/plain");
req.setAttribute("k", "v");
req.setAttribute("k", "v");
req.removeAttribute("k");

※和之前的大同小異