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Yes. The java bean must have a no-arg constructor with 'public' access level. In useBean tag if an object with the scope does not exists a freash new instance is created by container by calling it's public no-arg consructor and assigned to the 'id' parameter in useBean tag. All these work happen in background by container. regds maha anna |
This question troubles me long time ago and i did not bother to find it out until recently. When creating a bean for jsp, my bean will work perfectly well if i don't include a constructor explicitly. If i provide a constructor for the bean, errors occur at . Can somebody give me some explanation? Thanks a lot. |
I have a case where I am using a third party bean and want to do a use:bean in my jsp. During the constructor method of the bean it attempts to connect to a server. If the connect is unsuccessful, an error is thrown. In my case, if I can't connect, that's ok, I just want to hide a button on ... |
init() is an instance method. This means that, in order for the servlet to invoke init() it needs to have an instance of your servlet. aServlet.init(); In order to have a instance of your servlet, the servlet container needs to have executed an statement which might look like this: aServlet = new YourServlet(); I.e. the constructor gets executed first. Morale of ... |
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Hi bis No doubt u can create constructor in servlet ,servlet will compile and run. but you have to call your constructor explicitly as servlet engine will go only for methods described for life cycle of servlet. So in that case what ever you write in your servlet outside life cycle , it would be treated as a normal method by ... |
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Originally posted by Mohit Agarwal: Hi, I had searched a lot on this issue before posting a query regarding the same. I can define a no-arg constructor in my servlet class & perform some initializations then why do i need to use the init() method . I really didn't got any answer which pin-points to the issue . Please throw more ... |
This is a often asked question in this forum, and rightfully so, as it is an important part of understanding the lifecycle of a servlet. Bear summed it up in his response, but if you want to see some more in depth answers, search this forum for "init() constructor" and you will find several threads dealing with this issue. If you ... |
If your servlet class has a constructor with parameters, it will never be called by the servlet container. If your servlet class has a public arg-less constructor, it will be called. Generally speaking, instance variables one might use in a servlet are related to the servlet environment - for example initialization parameters read from web.xml. Therefore they should be initialized in ... |
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The other issue here is that specifying that a subclass must have a constructor with a particular signature is a design that can't be enforced. That's just one more thing to go wrong. Whereas an "init" method can be specified in the superclass, or the interface, and if subclasses need to override it they can. But if they don't override it, ... |
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I'm sure that I disagree. In Java, the default, no-arg constructor is only created for you if you don't explicitly create any other constructors. So, if you create a constructor that takes arguments (which would be absolutely useless) and don't explicitly create a zero arg constructor, the container will not be able to instanciate your servlet. The container calls the zero ... |
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Well, the Servlet is instantiated by the Container, as long as you have a default constructor you could define any additional constructor that you want, but they will never be invoked, because the container will not use them and you cannot instantiate servlet yourself (at least not if you intend to use it in the container :-) ) You have other ... |
String referer=req.getHeader("Referer"); HttpSession session=req.getSession(); String userID=(String)session.getAttribute("userID"); if(userID==null || userID.equals("") || userID.equalsIgnoreCase("null")){ Login refer=new Login(referer); out.println(wp.pagePrint1()+ "
Please Login"+ wp.pagePrint2()); } else { } My Login.java ============= import java.io.*; import java.sql.*; import javax.servlet.*; import javax.servlet.http.*; public class Login extends HttpServlet{ Connection cnn=null; ResultSet rs=null; String referer=""; public Login(String refLink){ referer=refLink; } public void doPost(HttpServletRequest req, HttpServletResponse res)throws IOException, ServletException{ res.setContentType("text/html"); PrintWriter out=res.getWriter(); ... |
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In applications using Beans, POJOs and JSP and all the usual stuff, I've had one question that I've never seen a definitive answer. Assuming a standard container like Glassfish, Tomcat, or JBoss, when is the Bean's constructor called? Is it for every evocation of the bean? Or are bean objects sometimes reused? is there a single answer? or does it vary ... |
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I read 2 conflicting things in 2 different places. One says a constructor needs to run before the init() method can be run, because a constructor creates an object while the init() method gives the object servlet-specific capabilities. The other says that a constructor can replace the init() method, and everything that is done in the init() method can be done ... |
a servlet is meant to be a controller... From the code you posted, i understand that you want to make a textbox from a servlet or something?? why do you use public textbox1(){ System.out.println("Hello world"); } and textbox1 box=new textbox1(); and pw.println("box object is " + box); ?? again, a servlet is a kind of controller, not a textbox-object or something... ... |
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