Usebean Tag
What are the advantages of usebean tags in jsp.
Is there any benefits, if i'm not using any SQl queries in JSP.
If i used Javabeans set & get methods and store them in a vector, in a web application. How far it will increase the performaance?
Its not a question of performance.
Its a question of design and maintainability.
Pages with lots of java scriptlet code mixed in with HTML are difficult to read and understand, and harder to maintain than JSPs with no scriptlet code.
The same reason for not including sql code in your JSP.
The aim is to have the SQL code in ONE place, so if it changes, then you only have to change it in one place.
If you have bits of SQL scattered through 5-6 jsp pages it becomes that much more difficult.
Similar Messages
-
How to use "scope " attrubute in useBean tag
Can anyone please tell me if I can use the same JavaBean Class to hold information form different pages? well, let me explain exactely what I want to do:
I have a Java bean Class that holds a property 'Name':
package ContactManager;
public class Person {
private String name="%";
public String getName () {
return this.name;
public void setName (String my_name) {
name = my_name + "%" ;
I'm using this class to store temporarly the Criteria of search from a JSP/HTML page to send to a database for search and for UPDATE -> this of course is done in different HTML/JSP pages. The problem I have is that the first time I set the properties (when the user make a search) this value remains unchanged [-> the second time when the user asks for update, I try to use the same bean to keep the value => unfortuntly it returns me the old value]
My question is: is the use of 'scope' attribute of the "jsp:useBean" tag can solve this problem? if yes how to use it? I've tryed to set the scope of the bean to page but that does not help :-(
Pleaze help, I'm stuck.... Bellow is the 4 JSP pages for:
- person_search.jsp / person_result.jsp
- request_modify.jsp/ DoModify.jsp
1 -person_search.jsp
<%@ page import="java.sql.*" %>
<HTML>
<HEAD><TITLE>Person Search</TITLE></HEAD>
<BODY><CENTER>
<form method="POST" action="person_result.jsp">
Name <input type="text" name="name" size="47"></p>
<input type="submit" value="Submit" name="B1">
<input type="reset" value="Reset" name="B2"></p>
</form></body>
</html>
2- person_result.jsp
<%@ page import="java.sql.*" %>
<HTML><BODY>
<jsp:useBean id="theBean" class="ContactManager.Person"/>
<jsp:setProperty name="theBean" property="*" />
Name<BR>
<%
try {
Class.forName("sun.jdbc.odbc.JdbcOdbcDriver");
System.out.println("JDBC driver loaded");
catch (ClassNotFoundException e) {
System.out.println(e.toString());
%>
<%
try {
Connection con = DriverManager.getConnection("jdbc:odbc:ContactManager");
Statement s = con.createStatement();
String sql = "SELECT Client.ClientID, Client.Name FROM Client where Client.Name like " + "'" + theBean.getName() + "'";
ResultSet rs = s.executeQuery(sql);
while (rs.next()) {
String myId = rs.getString(1);
%>
<TR>
<TD><%= myId %></TD>
<TD><a href="person_detail.jsp?id=<%= myId %>"><%=rs.getString(2)%></a></TD>
<TD><a href="delete_person.jsp?id=<%= myId %>">Delete</a></TD><BR>
</TR>
<%
rs.close();
s.close();
con.close();
catch (SQLException e) {
System.out.println(e.toString());
catch (Exception e) {
System.out.println(e.toString());
%>
</BODY>
</HTML>
3- request_modify.jsp
<%@ page import="java.sql.*" %>
<html>
<head><title>AddressBook: Modifying Person <%= request.getParameter ("id") %></title> </head>
<body bgcolor="#ffffee">
<%
try {
Class.forName("sun.jdbc.odbc.JdbcOdbcDriver");
System.out.println("JDBC driver loaded");
catch (ClassNotFoundException e) {
System.out.println(e.toString());
%>
<%
int rowsAffected = 0;
try {
Connection con = DriverManager.getConnection("jdbc:odbc:ContactManager");
Statement s = con.createStatement();
String sql = "SELECT Client.ClientID, Client.Name FROM Client where ClientID ="+ request.getParameter("id");
ResultSet rs = s.executeQuery(sql);
if (rs.next()) {
%>
Client Name is <input type=text name=name value=<%= rs.getString(2) %>> <br>
<TD><a href="person_do_modify.jsp?id=<%= rs.getString(1)%>">Confirm Modify</a></TD>
<%
rs.close();
s.close();
con.close();
catch (SQLException e) {
System.out.println(e.toString());
catch (Exception e) {
System.out.println(e.toString());
%>
</BODY> </HTML>
4- do_modify.jsp
<%@ page import="java.sql.*" %>
<html>
<head><title>AddressBook: Modifying Address <%= request.getParameter ("id") %></title></head>
<body bgcolor="#ffffee">
<jsp:useBean id="theBean" class="ContactManager.Person" scope="page"/>
<jsp:setProperty name="theBean" property="name"/>
<%
try {
Class.forName("sun.jdbc.odbc.JdbcOdbcDriver");
System.out.println("JDBC driver loaded");
catch (ClassNotFoundException e) {
System.out.println(e.toString());
%>
<%
int rowsAffected = 0;
try {
Connection con = DriverManager.getConnection("jdbc:odbc:ContactManager");
PreparedStatement preparedStatement = con.prepareStatement ("UPDATE Client SET Name=? WHERE ClientID =?");
preparedStatement.setString (1, theBean.getName());
preparedStatement.setString (2, request.getParameter("id"));
rowsAffected = preparedStatement.executeUpdate ();
preparedStatement.close ();
if (rowsAffected == 1) {
%>
done
<%
else{
%>
Not Modified
<%
con.close();
catch (SQLException e) {
System.out.println(e.toString());
catch (Exception e) {
%>
</BODY></HTML>
Thank you for the help.
SammyWhile a quick search on the <jsp:useBean> tag and the scope attribute will probably yield more information than I can summarize in a few sentences, I'm pretty sure that using the scope="page" attribute on a bean will cause that bean to be instantiated every time the page is loaded. In order for a bean to persist longer than the existance of that page (whether you're loading a new page, or reloading the same one), you'd need to set the scope to session or application (you'd probably want session).
-
Using variables in a jsp:useBean tag
I was wondeing if it is possible in any way to use variables in a jsp:useBean tag. Here is an example of what I am trying to do.
<%
String beanType = request.getParameter( "bean" );
if( beanType.equals( "Bean1" ) ) {
beanClass = "com.myCompany.Bean1";
} else {
beanClass = "com.myCompany.Bean2";
%>
<jsp:useBean name="<%= beanType %>" class="<%= beanClass %>"/>
I also tried using this approach
<%
if( beanType.equals( "Bean1" ) ) {
%>
<jsp:useBean id="bean" class="com.myCompany.Bean1"/>
<%
} else if( beanType.equals( "Bean2" ) ) {
%>
<jsp:useBean id="bean" class="com.myCompany.Bean2"/>
<%
%>
Neither approach seems to work. Is there any way around this problem?
Thanks,
Marcus.Hi,
check:
http://forum.java.sun.com/thread.jsp?forum=45&thread=398998&tstart=75&trange=15 -
How can i load A gui JTable bean through jsp:useBean tag in a jsp page
Hi,
i am chiranjit , i am in a jsp project . i am desparately looking a solution for below stated problem:
i want to make a jsp page for master entry , that why i want to load a GUI Java bean in my jsp page.This GUI Bean contaning a JTable in which allow grid type data entry in the jsp page. But i am unable load that bean in the jsp page through jsp:useBean tag in my page.So if you have any solution then send in the forum as early as possible.
Thank you
chiranjitNo can do. JSPs can only output plain HTML (and javascript...) They are not used like normal Java classes.
If you need a complex GUI then you might use an Applet instead. If you want to use a JSP then you are stuck using normal HTML components, like <table> <form...> <input type="text"> etc... -
Calling an inner class in a jsp:usebean tag
Hi everybody !
Here's my problem : working in my project on multiple pages, I'm using inner classes/beans to limitate my '.java' files but I'm stuck when calling that 'inner-bean' in my jsp:usebean tag.
First, I tried to declare in the class parameter : 'class="MyPrincipalBean.theInnerBean" but jsp returns me a 'not found' message.
I tried an other issue with this :
'class="MyPrincipalBean$theInnerBean" but I encountered a 'Attempt to use a bean type without a void constructor in jsp:useBean tag (JSP 1.1 specification, 2.13.1)'. Since I can't find that specification, I'm sending an SOS.
Am I on the good way ? If somebody as encoutered that sort of problem, it would be very kind of you to help me.
Thanks for your help !
[email protected]Thanks for your help!
I must recognize that my explainations weren't really precise.
My principal bean owns a table of my inner-class type :
public class FirstBean extends EntityBean {
private SecondBean[] tabSB;
public SecondBean[] getTabSB() {...}
public void setTabSB(SecondBean[] p_tabSB) {...}
public class SecondBean {...}
So I can call a specific bean from the tab in my Servlet for another page.
But I think I have the solution and I need your advise :
I tried this :
<jsp:useBean id="FirstBean" class="<...>.FirstBean" scope="session" />
<jsp:useBean id="SecBean" beanName="<...>.FirstBean$SecondBean" type="<...>.FirstBean$SecondBean" scope="request" />
And would you believe it ? It seems to work ! But I have to test this farther to be sure. What do you think of it ? -
Make sure that your bean is implementing the serializable interface and that
you are accessing the bean from the session with the same name.
Bryan
"Sandeep Suri" <[email protected]> wrote in message
news:[email protected]..
Hi, I have quick question about use of USEBEAN tag in SP2. When I
specify a scope of SESSION for the java bean, it does not keep the
values that I set for variable in the bean persistent.Thanks,Sonny
Try our New Web Based Forum at http://softwareforum.sun.com
Includes Access to our Product Knowledge Base! -
WL5.1: Using JSPC with pages that include usebean tags
Hi All,
I'm trying to get JSPC to correctly compile my JSP pages (which compile with
no problems from within Weblogic itself) and for each page that contains a
<userbean> tag, it seems as though java is trying to instantiate the bean as
it turns the JSP page into a servlet.
I can stop this happening by changing the <usebean class="foobar"/> tag to a
<usebean type="foobar"/>, but according to the documentation, this technique
is only supposed to be used when the bean's object is expected to be in
scope already, which is not the case.
Is there anyway to tell JSPC not to instantiate the beans in the <usebean>
tags?
bye
Hi All,
I'm trying to get JSPC to correctly compile my JSP pages (which compile with
no problems from within Weblogic itself) and for each page that contains a
<userbean> tag, it seems as though java is trying to instantiate the bean as
it turns the JSP page into a servlet.
I can stop this happening by changing the <usebean class="foobar"/> tag to a
<usebean type="foobar"/>, but according to the documentation, this technique
is only supposed to be used when the bean's object is expected to be in
scope already, which is not the case.
Is there anyway to tell JSPC not to instantiate the beans in the <usebean>
tags?
bye
-
when I use
<jsp:useBean id="addressBean" class="AddressBean" scope="session"/>
I get the following error
Exception Details: org.apache.jasper.JasperException
Unable to compile class for JSP No Java compiler was found to compile the generated source for the JSP. This can usually be solved by copying manually $JAVA_HOME/lib/tools.jar from the JDK to the common/lib directory of the Tomcat server, followed by a Tomcat restart. If using an alternate Java compiler, please check its installation and access path.
So my question is how to use the <jsp:useBean> tag in JSCPlease see my message How to set developer's mode for oracle jsp engine.
As a very early warning of the future, this way of setting configuration paramemter in web.xml for oracle jsp engine will be deprecated in the next major version of oc4j and desupported probably later on. Yes, it is still supported in 10.1.3 and the next major version, though. -
Need help with the jsp:useBean tag
Dear Fellow Java/JSP developers:
I am trying to use the <jsp:useBean> tag in a jsp that displays the values from a javaBean that gets populated by another class.
<%@ page contentType="text/html" pageEncoding="UTF-8"%>
<%@ page import = "java.util.ArrayList"%>
<%@ page import = "java.util.Iterator"%>
<%@ page import = "salattimes.CalendarParse" %>
<%@ page import = "salattimes.Salat" %>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"
"http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>JSP Page</title>
</head>
<body>
<jsp:useBean id="test" scope="session" class="calendar.Time" />
<% CalendarParse sTime = new CalendarParse();
Time mytime = sTime.runExample();%>
<%=mytime.getA() %>
<%=mytime.getB() %>
<%=mytime.getC() %>
<%=mytime.getD() %>
<%=mytime.getE() %>
</body>
</html>However, up to now, I am only able to display the values on my JSP page using the scriptlet
<% CalendarParse sTime = new CalendarParse();
Time mytime = sTime.runExample();%> to declare and create the object (the method call sTime.runExample(); populates the fields in the Java Bean), and the expressions:
<%=mytime.getA() %>
<%=mytime.getB() %>
<%=mytime.getC() %>
<%=mytime.getD() %>
<%=mytime.getE() %>to present the values on the screen. What I would like to do is assign the object that I create to a javaBean reference declared in a <jsp:useBean> tag as follows:
<jsp:useBean id="test" scope="session" class="calendar.Time" />
<% CalendarParse sTime = new CalendarParse();
test = sTime.runExample();%>and then present the values stored in the bean to the JSP page as follows:
<jsp:getProperty name="test" property="a" />
<jsp:getProperty name="test" property="b" />
<jsp:getProperty name="test" property="c" />
<jsp:getProperty name="test" property="d" />
<jsp:getProperty name="test" property="e" />
<jsp:getProperty name="test" property="f" />Is this possible? When I try the above, I get "null" as my output on the screen. When I try the first approach listed above, I get the values I am looking for. Is there a way to accomplish this using the <jsp:useBean> approach?
Thanks to all those who reply.
Sincerely;
FayyazThe code:
<jsp:useBean id="calendar" class="calendar.CalendarParse" scope="session"/>
<c:set var="time" value="${calendar.time}"/>Would be roughly equivalant to:
calendar.CalendarParse calendar = new calendar.CalendarParse();
Object time = calendar.getTime();I assumed that the CalendarParse object was in the calendar package because that was were your Time class was (when you used <jsp:useBean id="test" scope="session" class="calendar.Time" />"), but when I look back at your original post I see I was wrong and the use of calendar as both the incorrect package and the variable name was confusing. To make the code more similar to your original post the code should have read:
<jsp:useBean id="sTime" class="salattimes.CalendarParse"/>
<c:set var="myTime" value="${sTime.time}" scope="session"/>
${myTime.a}
${myTime.b}
${myTime.c}
etc...Here is an explanation of the parts:
/* name of the variable */ /* fully qualified class name, package.className */
<jsp:useBean id="sTime" class="salattimes.CalendarParse"/>
/* name of the new object from bean */ /* source of object, variable.property */ /* Scope of new object */
<c:set var="myTime" value="${sTime.time}" scope="session"/>
/* data to display variable.property */
${myTime.a}Where a 'property' in a bean is defined as a method in the form of getProperty(). So the 'time' property is getTime() and the 'a' property is getA(). -
JSP - useBean tag works only for first request
hey why donnu change the scope to PAGE, give a try.........
Vishal Vishnoi wrote:
> Using Weblogic 5.1 I am trying to work with a simple example of a JSP
> page which has got a usebean tag. The tag is
>
> <jsp:useBean id="resourceTypes" type="java.util.ArrayList"
> scope="request" />
>
> * This works only the first time I load the page.
>
> If I try to load the page again. I get the following error
>
> javax.servlet.ServletException: Could not find bean 'resourceTypes',
> type 'java.
> util.ArrayList' in scope
>
> --Vishal
-
Constructor parameter and useBean -tag
Greetings,
Is there a way to pass a contructor parameter when using the JSP tags:
<%@ page import="DBTool" %>
<jsp:useBean id='manager' scope="application" class=DBTool/>
The DBTool class needs init parameters in the contructor, but I don`t know any way how to do it when using the useBean tag?
Regards,
EkiThis is as close as you are going to get. The code within the jsp:useBean tag will only get executed when the object needs to be created. With a scope of application, it will only get run once unless you call application.removeAttribute("manager") OR getServletContext().removeAttribute("manager").
Hope this helps
<%@ page import="DBTool" %>
<jsp:useBean id="manager" scope="application" class="DBTool">
<%
manager.setProperty1(13);
manager.setMyProperty2("MyProperty");
%>
</jsp:useBean>OR if you want it to be cleaner
<%@ page import="DBTool" %>
<jsp:useBean id="manager" scope="application" class="DBTool">
<% manager.init(parms); %>
</jsp:useBean> -
ConnCacheBean sample and useBean tag?
Hi,
In the ConnCacheBean sample code (JDBC 9i Sample Code), the Bean is instantiated in a scriptlet in each of the JSPs in the example:
// Instantiate and get instance of the Bean
ConnCacheBean myBean = ConnCacheBean.getInstance();
If you are using ConnCacheBean from more than one JSP, would it make more sense to have a useBean tag with application scope in each JSP:
<jsp:useBean id="ccb" class="packagename.ConnCacheBean" scope="application">
Just wondering if there is any particular reason that I am missing, that the code was written in the way it was?
thanks
RobRobert,
I would suggest you to keep this class as a singleton class. This is because, at any time, there should be only one copy of this class on the server or the JVM. Multiple copies of this class means that there is more than one place from where a class/JSP can get a connection. This means that the connection is instantiated more than once which defeats the whole purpose of Caching connections. You should avoid this.
What you are suggesting is fine if you are writing a small application, but you dont want multiple copies of this class even by mistake in a big application.
Thanks. -
I have a small login application that uses JSP pages and servlets and EJBs. The flow of the application is as follows:
login form (jsp) posts to:
servlet that calls a login method of a bean, redirects to:
logged in page (jsp) links to:
change password form (jsp) post to:
servlet that calls bean method to change password, redirects to:
logged in page.
My question:
The bean with the login method is first created on the login form with a useBean tag. This one works just fine. However the bean with the change password method cannot be found with a request.getAttribute as the other bean can be. This is true when I first create this bean on the change password form with a use bean tag. Strangly enough if I put this useBean tag on the login form (the page I run from Jdeveloper) I have no problem using the request.getAttribte method. Both beans have a scope of session.
Can any tel me why this is?
nullThank you very much! My problem has been solved. I did not know that JBOSS or Tomcat do not support non packaged java bean any more.
Xin -
How to Implement jsp:useBean tags
Hi,
I hav a trouble with using the Tag jsp:useBean
Actually im using Tomcat4.1 webserver'
I created a java file and compiled that
When i included that class file,The Jsp Compiler seeming me a error that the Required class in not found
Actually wht my problem is that i cannot find out the storage locations for the corresponding files
I know where to save the jsp
but i need to know where to put the class file and its source.Bcz that one which i want to use in that tag{<jsp:useBean>}
I want to know what should i do
With Regards
Ganesh BBeans are regular Java classes that follow particular conventions defined by the JavaBean's specification. The don't extend from a particular class, they aren't packaged in a particular package, and - germane to the question - they aren't located in a special place on the server. The classes which are loaded into the JSP by the <jsp:useBean> construct are located in the same location as other classes in a web application. They are located in the classes directory of the WEB-INF directory of the web application directory itself. Or, if you bundle your classes into a jar file, then the jar file will be located in the lib directory of the WEB-INF directory. In either case, remember to use packages for your classes including your beans.
-
" ')' expected " Error when compile jsp that use useBean tag
I'm using JDeveloper 10.1.3 and I have a page with a next jsp tag
<jsp:useBean id="objectid" type="package.MyClass" scope="application"/>
When I compile this JSP page, I got the error:
')' expected
If the application is deployed in the J2EE container like Tomcat or OC4J, the page works fine.
Is this a JDeveloper bug?? What Can I do?The JSP page works fine in OC4J 10.1.2, but in the OC4J 10.1.3 it throws the same error.
The soruce code that the container generates is this:
if ((objectid= (package.MyClass) pageContext.getAttribute( "objectid", PageContext.APPLICATION_SCOPE)) == null) {
throw new InstantiationException("No se ha encontrado el bean "objectid" en el ámbito "application"");
The bug consist in the generation of the servlet source code. The double quotation is the problem, for that, the compiler generates the error ')' expected...
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