Problem with retreving the Attribute in jsp
Varun Nayudu
Ranch Hand
Posts: 160
posted 7 years ago
I am trying to test how a attribute is displayed in the jsp when using a bean
I am using a bean Person.java ->name (as property)
the index page takes a name from the client and sends to the servlet ,the servlet takes that request parameter and stores in a object person and stores the object in the Attribute and sends to the first.jsp page
here is the code
index.jsp
web.xml
Person.java (bean)
Output
My question is why is the standard action and EL not working and displaying the name .......
I am using a bean Person.java ->name (as property)
the index page takes a name from the client and sends to the servlet ,the servlet takes that request parameter and stores in a object person and stores the object in the Attribute and sends to the first.jsp page
here is the code
index.jsp
web.xml
Person.java (bean)
Output
My question is why is the standard action and EL not working and displaying the name .......
SCJP 1.5, SCWCD 1.5
Tomasz Szymanski
Greenhorn
Posts: 23
posted 7 years ago
Because obviously the bean is placed under "pObj" in the request scope. Under what attribute name do you think the standard action and the EL expression are trying to find your bean?
Varun Nayudu wrote:
My question is why is the standard action and EL not working and displaying the name .......
Because obviously the bean is placed under "pObj" in the request scope. Under what attribute name do you think the standard action and the EL expression are trying to find your bean?
tangara goh
Ranch Hand
Posts: 258
posted 7 years ago
Chance upon this and can't help to ask you question :-
Sorry Tomasz Szymansik, could you please elaborate your comments, especially the part on "obviously the bean is placed under "pObj" in the request scope."
It would be most helpful if you can tell what should be the correct methods....am trying to learn as much as possible from experts in this forum. Thank you.
Tomasz Szymanski wrote:Varun Nayudu wrote:
My question is why is the standard action and EL not working and displaying the name .......
Because obviously the bean is placed under "pObj" in the request scope. Under what attribute name do you think the standard action and the EL expression are trying to find your bean?
Chance upon this and can't help to ask you question :-
Sorry Tomasz Szymansik, could you please elaborate your comments, especially the part on "obviously the bean is placed under "pObj" in the request scope."
It would be most helpful if you can tell what should be the correct methods....am trying to learn as much as possible from experts in this forum. Thank you.
D. Ogranos
Ranch Hand
Posts: 214
posted 7 years ago
I assume you want to compare the access of scoped variables with scriptlets and EL? Some things I see here:
- <jsp:useBean...> looks for a bean named "person". Tomasz Szymanski pointed this out, if you want to use the same object as with the scriptlet, you should write id="pObj". Your EL expression would then access it with ${pObj.name}.
- You use <jsp:useBean..> with the class attribute. This creates a new Person object in the request scope, which attributes will be null of course (since your Person object does not have a default constructor that sets another value). If you want to use an existing object, you should write type="com.beans.Person" instead of class="..".
- I don't think you need <jsp:getProperty..> here (might depend on which JSP/EL version you are using).
- Yet another thing: I *think* you can leave out the <jsp:useBean..> completely. The EL expression is smart enough to look into the different scopes by itself. However I usually do write <jsp:useBean..> (with type attributes) at the beginning of a jsp to document which beans the page expects. Note that <jsp:useBean..> will throw a nullpointer exception if the objects are not found in scope, so this is also a useful way to find mistakes quickly.
- <jsp:useBean...> looks for a bean named "person". Tomasz Szymanski pointed this out, if you want to use the same object as with the scriptlet, you should write id="pObj". Your EL expression would then access it with ${pObj.name}.
- You use <jsp:useBean..> with the class attribute. This creates a new Person object in the request scope, which attributes will be null of course (since your Person object does not have a default constructor that sets another value). If you want to use an existing object, you should write type="com.beans.Person" instead of class="..".
- I don't think you need <jsp:getProperty..> here (might depend on which JSP/EL version you are using).
- Yet another thing: I *think* you can leave out the <jsp:useBean..> completely. The EL expression is smart enough to look into the different scopes by itself. However I usually do write <jsp:useBean..> (with type attributes) at the beginning of a jsp to document which beans the page expects. Note that <jsp:useBean..> will throw a nullpointer exception if the objects are not found in scope, so this is also a useful way to find mistakes quickly.
posted 7 years ago
Only if the scoped variable does not already exist. If a person scoped variable exists, the tag will do nothing (except create a useless scripting variable).
Using type will never cause a new instance to be created, but class can be used, as noted above, to hook up to an existing scoped variable.
getProperty is no longer needed in the JSTL and EL environment.
Correct. useBean is not necessary for the EL to find the scoped variable.
D. Ogranos wrote:You use <jsp:useBean..> with the class attribute. This creates a new Person object in the request scope,
Only if the scoped variable does not already exist. If a person scoped variable exists, the tag will do nothing (except create a useless scripting variable).
If you want to use an existing object, you should write type="com.beans.Person" instead of class="..".
Using type will never cause a new instance to be created, but class can be used, as noted above, to hook up to an existing scoped variable.
I don't think you need <jsp:getProperty..> here (might depend on which JSP/EL version you are using).
getProperty is no longer needed in the JSTL and EL environment.
I *think* you can leave out the <jsp:useBean..> completely.
Correct. useBean is not necessary for the EL to find the scoped variable.
