一、listener生命周期
listener是web三大組件之一，是servlet監(jiān)聽(tīng)器，用來(lái)監(jiān)聽(tīng)請(qǐng)求，監(jiān)聽(tīng)服務(wù)端的操作。
listener分為：（都是接口類，必須實(shí)現(xiàn)相應(yīng)方法）
1.生命周期監(jiān)聽(tīng)器（3個(gè)）
|
1
2
3
4
5
6
7
8
9
|
servletcontextlistener requestdestroyed 在容器啟動(dòng)時(shí)被調(diào)用（在servlet被實(shí)例化前執(zhí)行）requestinitialized 在容器銷毀時(shí)調(diào)用（在servlet被銷毀后執(zhí)行）httpsessionlistenersessioncreated 在httpsession創(chuàng)建后調(diào)用sessiondestroyed 在httpsession銷毀前調(diào)用（執(zhí)行session.invalidate();方法）servletrequestlistenerrequestdestroyed 在request對(duì)象創(chuàng)建后調(diào)用（發(fā)起請(qǐng)求）requestinitialized 在request對(duì)象銷毀前調(diào)用（請(qǐng)求結(jié)束） |
2.屬性變化監(jiān)聽(tīng)器（3個(gè)）
|
1
2
3
4
5
6
7
8
9
10
11
|
attributeadded(servletcontextattributeevent event)向appliction中添加屬性時(shí)調(diào)用attributeremoved(servletcontextattributeevent event)從appliction中刪除屬性時(shí)調(diào)用attributereplaced(servletcontextattributeevent event)替換application中的屬性時(shí)調(diào)用httpsessionattributelistenerattributeadded(httpsessionbindingevent event)attributeremoved(httpsessionbindingevent event)attributereplaced(httpsessionbindingevent event)servletrequestattributelistenerattributeadded(servletrequestattributeevent event)attributeremoved(servletrequestattributeevent event)attributereplaced(servletrequestattributeevent event) |
以上監(jiān)聽(tīng)器接口除了傳參不同，方法名都是一樣的。分別監(jiān)聽(tīng)application，session，request對(duì)象的屬性變化。
3.session中指定類屬性變化監(jiān)聽(tīng)器（2）
|
1
2
3
4
5
6
|
httpsessionbindinglistener valuebound(httpsessionbindingevent event) 當(dāng)該類實(shí)例設(shè)置進(jìn)session域中時(shí)調(diào)用valueunbound(httpsessionbindingevent event) 當(dāng)該類的實(shí)例從session域中移除時(shí)調(diào)用httpsessionactivationlistener sessionwillpassivate(httpsessionevent se) sessiondidactivate(httpsessionevent se) |
二、測(cè)試范例
1.生命周期監(jiān)聽(tīng)：
servletcontentattribute_listener.java
|
1
2
3
4
5
6
7
8
9
10
11
12
13
|
public class servletcontentattribute_listener implements servletcontextlistener { /** * servletcontextlistener實(shí)現(xiàn)方法 * @param sce */ public void contextinitialized(servletcontextevent sce) { system.out.println("servletcontextlistener初始化"); } public void contextdestroyed(servletcontextevent sce) { system.out.println("servletcontextlistener銷毀"); }} |
其他兩個(gè)監(jiān)聽(tīng)器類似,不在重復(fù)貼出。
在web.xml中配置
|
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
|
<!-- 監(jiān)聽(tīng)器 --> <!-- servlet監(jiān)聽(tīng)器 --> <listener> <listener-class>study.mylistener.servletcontentattribute_listener</listener-class> </listener> <!-- session監(jiān)聽(tīng)器 --> <listener> <listener-class>study.mylistener.httpsessionattribute_listener</listener-class> </listener> <!-- request監(jiān)聽(tīng)器--> <listener> <listener-class>study.mylistener.servletrequestattribute_listener</listener-class> </listener> |
運(yùn)行結(jié)果：
2.屬性監(jiān)聽(tīng)：
servletcontentattribute_listener.java
|
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
|
public class servletcontentattribute_listener implements servletcontextattributelistener{ /** * servletcontextattributelistener實(shí)現(xiàn)方法 * @param event */ public void attributeadded(servletcontextattributeevent event) { string meg = messageformat.format("servletcontent添加屬性:{0},屬性值：{1}",event.getname(),event.getvalue()); system.out.println(meg); } public void attributeremoved(servletcontextattributeevent event) { string meg = messageformat.format("servletcontent刪除屬性:{0},屬性值：{1}",event.getname(),event.getvalue()); system.out.println(meg); } public void attributereplaced(servletcontextattributeevent event) { string meg = messageformat.format("servletcontent替換屬性:{0},屬性值：{1}",event.getname(),event.getvalue()); system.out.println(meg); }} |
另外兩個(gè)監(jiān)聽(tīng)器類似，不在贅訴。接下來(lái)用jsp頁(yè)面測(cè)試
listenerdemo.jsp
|
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
|
<%-- created by intellij idea. user: administrator date: 2017/10/17 time: 15:28 to change this template use file | settings | file templates.--%><%@ page contenttype="text/html;charset=utf-8" language="java" %><html><head> <title>監(jiān)聽(tīng)器設(shè)置</title></head><body> <% /** * servlet監(jiān)聽(tīng) */ application.setattribute("name","changxiang"); application.setattribute("name","小cai先森"); application.removeattribute("name"); /** * session監(jiān)聽(tīng) */ session.setattribute("sessionname","changxiang"); session.setattribute("sessionname","小cai先森"); session.removeattribute("sessionname"); session.invalidate(); /** * request監(jiān)聽(tīng) */ request.setattribute("requestname","changxiang"); request.setattribute("requestname","小cai先森"); request.removeattribute("requestname"); %></body></html> |
執(zhí)行結(jié)果如下：
注意：其中遇到一個(gè)問(wèn)題：就是在啟動(dòng)tomcat的時(shí)候servletcontextlistener監(jiān)聽(tīng)執(zhí)行了兩次，最后刪除掉server.xml中 context 的手動(dòng)配置，這樣就不會(huì)加載兩次了。
以上這篇基于listener監(jiān)聽(tīng)器生命周期(詳解)就是小編分享給大家的全部?jī)?nèi)容了，希望能給大家一個(gè)參考，也希望大家多多支持服務(wù)器之家。
原文鏈接：http://www.cnblogs.com/caijh/archive/2017/10/17/7683007.html
