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Jsp中訪問JavaBean入門

Posted on 2006-07-20 15:19 亮子閱讀(1505) 評論(0) 編輯收藏

先來介紹一下JavaBean
什么是JavaBean?
? JavaBean是一種可重復使用，且跨平臺的軟件組織．
? 分兩種：有用戶界面的JavaBean
????????? 沒有用戶界面的JavaBean,主要用來處理事務的JavaBean.通常所指的就是此種JavaBean.
JavaBean的特性?
? JavaBean是一個Public類
? JavaBean有一個不帶參數的構造方法　
　JavaBean通過setter,getter來設置和訪問屬性．
JSP訪問JavaBean?
????? 有兩種辦法來訪問JavaBean：
??????? 1)通過程序代碼
??????? 2)通過JSP標簽來訪問JavaBean
如何通過JSP標簽來訪問JavaBeans?
??????? 1)導入JavaBean類：　<%@ page import="my.SampleBean"%>
??????? 2)聲明JavaBean對象?。骸∈褂?lt;jsp:userBean id="myBean" class="my.SampleBean" scope="Session"/>
??????????????? id代表對象的變量名
??????????????? class指定JavaBean類名，必須是JavaBean的完整名稱．
??????????????? scope指定JavaBean對象的范圍
??????? 3)訪問JavaBean屬性：
??????????????? 訪問JavaBean屬性：　<jsp:getProperty name="myBean" property="xxx"/>
??????????????? 設置JavaBean屬性：　<jsp:setProperty name="myBean" property="xxx" value="0"/>
JavaBean的范圍.
??????? scope屬性決定JavaBean對象存在的范圍．scope可選值有四個：1)page 2)request 3)session 4)application. 默認page.

舉個例子先，

jsp文件如下：

<% @page?contentType = " text/html " ? %>
?2

<! DOCTYPE?html?PUBLIC? " -//W3C//DTD?XHTML?1.0?Transitional//EN " ? " http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd " >?
?3

<%@page?import="lonny.dbtest.User"%> 　
?4

<html>
?5

<head>
?7

????????<title>JSP?Page</title>
?8

</head>
?9

<body?bgcolor="#FFFFFF">
10

<jsp:useBean?id="myBean"?scope="page"?class="lonny.dbtest.User"??/> 
11

????????my?name?is?<jsp:getProperty?name="myBean"?property="userName"?/>? 
12

????????<%
13

????????????????User?user?=?null;
14

????????????????String?scope?=?null;
15

????????????????user?=?(User)request.getAttribute("myBean");
16

????????????????if?(user?!=?null)?scope??=?"request";
17

????????????????
18

????????????????user?=?(User)session.getAttribute("myBean");
19

????????????????if?(user?!=?null)?scope??=?"session";
20

????????????????
21

????????????????user?=?(User)application.getAttribute("myBean");
22

????????????????if?(user?!=?null)?scope??=?"application";
23

????????????????
24

????????????????if?(user?==?null)?scope?=?"page";
25

????????%>????????
26

????????scope?type??is?<%=scope%>
27

</body>
28

</html>
29

javabean User類文件User.java內容為：

package ?lonny.dbtest;
?2

public ? class ?User? {
?3

???????? public ?User(String?userID,?String?userName,?Sex?sex,?String?birthday,?String?password) {
?4

???????????????? this .userID? = ?userID;
?5

???????????????? this .userName? = ?userName;
?6

???????????????? this .sex? = ?sex.getSex();
?7

???????????????? this .birthday? = ?birthday;
?8

???????????????? this .password? = ?password;
?9

????????}
10

???????? public ?String?getBirthday()? {
11

???????????????? return ?birthday;
12

????????}
13

???????? public ? void ?setBirthday(String?birthday)? {
14

???????????????? this .birthday? = ?birthday;
15

????????}
16

???????? public ? boolean ?getSex()? {
17

???????????????? return ?sex;
18

????????}
19

???????? public ? void ?setSex(Sex?sex)? {
20

???????????????? this .sex? = ?sex.getSex();
21

????????}
22

???????? public ?String?getUserID()? {
23

???????????????? return ?userID;
24

????????}
25

???????? public ? void ?setUserID(String?userID)? {
26

???????????????? this .userID? = ?userID;
27

????????}
28

???????? public ?String?getUserName()? {
29

???????????????? return ?userName;
30

????????}
31

???????? public ? void ?setUserName(String?userName)? {
32

???????????????? this .userName? = ?userName;
33

????????}
34

???????? public ?String?getPassword()? {
35

???????????????? return ?password;
36

????????}
37

???????? public ? void ?setPassword(String?password)? {
38

???????????????? this .password? = ?password;
39

????????}
40

????????
41

???????? private ?String?userID;
42

???????? private ?String?userName;
43

???????? private ? boolean ?sex;
44

???????? private ?String?birthday;
45

???????? private ?String?password;
46

}
47

注意：上面的程序經編譯、部署，訪問會出現java.lang.InstantiationException異常．
這是因為JavaBean　User類需要有一個不帶參數的構造器．
添加此構造器后問題解決：

??????? public ?User() {

????????

???????}

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