doubt

[hemamalini nithyanandam]

i am just a beginner in jsp and servlet. i have written a servlet which returns a list containing string of names.(fromList). i want to display that using option tag in a web page. in my jsp file i have included

<%
	List fromList=(List)request.getAttribute("fromList");
	for(int i=0; i< fromList.size();i++)
	{
		
		String From=(String)fromList.get(i);
	}
	 %>
	 <select>
		<option value= <%=From %>> </option>

but i am getting error. how to display the list of strings using <select><option>

[Sunil Sunny]

hemamalini nithyanandam wrote:i am just a beginner in jsp and servlet. i have written a servlet which returns a list containing string of names.(fromList). i want to display that using option tag in a web page. in my jsp file i have included

<%
	List fromList=(List)request.getAttribute("fromList");
	for(int i=0; i< fromList.size();i++)
	{
		
		String From=(String)fromList.get(i);
	}
	 %>
	 <select>
		<option value= <%=From %>> </option>

but i am getting error. how to display the list of strings using <select><option>

Use this :
<select>
<%
List fromList=(List)request.getAttribute("fromList");

for(int i=0; i< fromList.size();i++)
{

String From=(String)fromList.get(i);
out.println("<option value='" + From + "'></option>");
}
%>
</select>

[Piyush Joshi]

First: Don't use scriptlets in JSP, use tags.
Second: use lower case letter for variables name (i.e. "String from" not "String From" )

But since you are a beginner then playing with scriptlets is ok.

What you are doing wrong here is you are accessing the From variable outside the loop. Remember whatever you write inside <% %> will be turned into java code and whatever you write outside will be shown as plain text on html page.
For example:

<%
 for(int i=0;i<2;i++){
%>
Plain Text
<%
}%>

Resultant java code will be something like:

for(int i=0; i<2;i++){
 out.print("Plain Text");
}

out.print("Plain Text") will just print "Plain Text" to your html page.

But if you write:

<%
 for(int i=0;i<2;i++){
%>
<%= i %>,
<%
}%>

Resultant java code will be:

for(int i=0; i<2;i++){
 out.print(i);
 out.print(",");
}

you will get 0,1, on the html page.

So now can you think what you need to do to print the list?

[Bear Bibeault]

Sunil Sunny wrote:Use this :

No do not. The suggestion to use scriptlets in JSP is a poor one. Scriplets and Java code in a JSP has been discredited for almost 10 years now. To be using Java code in a JSP in 2011 is nothing short of irresponsible.

If you are a beginner to JSP, it's important to learn best practice right off the bat. Learn the JSTL and EL and be sure to completely avoid scriptlets in JSP pages.

It will also be helpful to read these articles:

The Secret Life of JSPs

The Front Man

[hemamalini nithyanandam]

thanks a lot for the suggestions. but still i am getting error as

org.apache.jasper.JasperException: Unable to compile class for JSP: 

An error occurred at line: 68 in the jsp file: /index.jsp
From cannot be resolved
65: { 
66: 
67: String from=(String)fromList.get(i); 
68: out.println("<option value='" + From + "'></option>"); 
69: } 
70: %> 
71: </select>


Stacktrace:
	at org.apache.jasper.compiler.DefaultErrorHandler.javacError(DefaultErrorHandler.java:92)
	at org.apache.jasper.compiler.ErrorDispatcher.javacError(ErrorDispatcher.java:330)
	at org.apache.jasper.compiler.JDTCompiler.generateClass(JDTCompiler.java:439)
	at org.apache.jasper.compiler.Compiler.compile(Compiler.java:356)
	at org.apache.jasper.compiler.Compiler.compile(Compiler.java:334)
	at org.apache.jasper.compiler.Compiler.compile(Compiler.java:321)
	at org.apache.jasper.JspCompilationContext.compile(JspCompilationContext.java:592)
	at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:328)
	at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:313)
	at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:260)
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:290)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
	at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:233)
	at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:191)
	at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:127)
	at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:102)
	at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109)
	at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:291)
	at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:859)
	at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:602)
	at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:489)
	at java.lang.Thread.run(Unknown Source)

will start learning jstl from nowonwards.

[hemamalini nithyanandam]

this is my servlet

public class Display extends HttpServlet{
	
	
	private static final long serialVersionUID = 1L;
	
	private Login logs=new Login();
	
	public Display() {
		super();
		// TODO Auto-generated constructor stub
	}
	protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		doPost(request, response);
	}

	/**
	 * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
	 */
	protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
	
		
		String from = request.getParameter("from");
		String to = request.getParameter("to");
		
		
		System.out.println("From::" + from + ", To::" + to );
		
		List<String> fromList = getFrom(from);
		List<String> toList=getTo(to);
		request.setAttribute("fromList", fromList);
		request.setAttribute("toList",toList);
		
		RequestDispatcher rd = request.getRequestDispatcher("/index.jsp");
		rd.forward(request, response);
	}
	private List<String> getFrom(String from){
		List<String> FromList=logs.getdistinctFrom();
		return FromList;
	}
	private List<String> getTo(String to){
		List<String> ToList=logs.getdistinctTo();
		return ToList;
	}
	
}

[Sunil Sunny]

An error occurred at line: 68 in the jsp file: /index.jsp
From cannot be resolved
65: {
66:
67: String from=(String)fromList.get(i);
68: out.println("<option value='" + From + "'></option>");
69: }
70: %>
71: </select>

Look at this carefully "From" is not same as "from".

String from=(String)fromList.get(i);

here from is small case.

68: out.println("<option value='" + From + "'></option>");

here "From" is camel case.

So a variable problem

[Bear Bibeault]

The first step is stop using Java in the JSP. If you insist on proceeding with poor practices then at least stop using out.print()! That's an abomination. The whole purpose of using a JSP is so that you don't need to build up HTML in JaVa strings!

As a beginner you are making a very poor start in learning JSP by following very poor practices.

[Piyush Joshi]

hemamalini nithyanandam wrote:thanks a lot for the suggestions. but still i am getting error as

org.apache.jasper.JasperException: Unable to compile class for JSP: 

An error occurred at line: 68 in the jsp file: /index.jsp
From cannot be resolved
65: { 
66: 
67: String from=(String)fromList.get(i); 
68: out.println("<option value='" + From + "'></option>"); 
69: } 
70: %> 
71: </select>

will start learning jstl from nowonwards.

Error message says it all: "From cannot be resolved."

[Sunil Sunny]

Well Bear you are an author . written books on jQuery. I will surely read your book as i had to interact with Jquery

[hemamalini nithyanandam]

Oct 27, 2011 8:52:37 PMorg.apache.jasper.JasperException: An exception occurred processing JSP page /index.jsp at line 64

61: <% 
62: List fromList=(List)request.getAttribute("fromList"); 
63: 
64: for(int i=0; i< fromList.size();i++) 
65: { 
66: 
67: String from=(String)fromList.get(i); 


Stacktrace:
	org.apache.jasper.servlet.JspServletWrapper.handleJspException(JspServletWrapper.java:521)
	org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:430)
	org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:313)
	org.apache.jasper.servlet.JspServlet.service(JspServlet.java:260)
	javax.servlet.http.HttpServlet.service(HttpServlet.java:717) org.apache.catalina.core.StandardWrapperValve invoke
SEVERE: Servlet.service() for servlet jsp threw exception
java.lang.NullPointerException
	at org.apache.jsp.index_jsp._jspService(index_jsp.java:120)
	at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
	at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:388)
	at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:313)
	at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:260)
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:290)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
	at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:233)
	at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:191)
	at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:127)
	at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:102)
	at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109)
	at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:291)
	at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:859)
	at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:602)
	at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:489)
	at java.lang.Thread.run(Unknown Source)

still getting error

[hemamalini nithyanandam]

will change to jstl .. will change the practice from now onwards. thank you so much for the suggestions

[Sunil Sunny]

hemamalini nithyanandam wrote:will change to jstl .. will change the practice from now onwards. thank you so much for the suggestions

Ok that's good to learn jstl but see how to trace the error the error isin line : 64 saying clearly that your fromlist is null i.e. has nothing in it . that's why you are getting an error.

[Piyush Joshi]

Well, much have been said by Bear.
But one thing I will point out that for a beginner to better understand how JSP page gets translated, its very helpful to look at the servlet source code generated by the JSP compiler. If you understand translation good enough then you can use Tags and EL very effectively.

[hemamalini nithyanandam]

oh . started with head first servlets and jsp. ..

in that prog is there anything wrong with servlet code

public class Display extends HttpServlet{
	
	
	private static final long serialVersionUID = 1L;
	
	Login logs=new Login();
	
	public Display() {
		super();
		// TODO Auto-generated constructor stub
	}
	protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		doPost(request, response);
	}

	/**
	 * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
	 */
	protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
	
		
		
		
		List<String> fromList = getFrom();
		List<String> toList=getTo();
		request.setAttribute("fromList", fromList);
		request.setAttribute("toList",toList);
		
		RequestDispatcher rd = request.getRequestDispatcher("/index.jsp");
		rd.forward(request, response);
	}
	private List<String> getFrom(){
		List<String> fromList=logs.getdistinctFrom();
		return fromList;
	}
	private List<String> getTo(){
		List<String> ToList=logs.getdistinctTo();
		return ToList;
	
	}
}

and this is my Login class . i checked this class. it works. so prob is either in servlet or in jsp.

public class Login extends AbstractQOSDAO{
	public List<String> getdistinctFrom(){
		Connection con=getConnection();
		List<String> fromVO=new ArrayList<String>();
		String query="SELECT DISTINCT SRC FROM COSTDIS";
		try{
			Statement stmt=(Statement) con.createStatement();
			ResultSet set=stmt.executeQuery(query);
			while(set.next())
			{
				fromVO.add(set.getString("SRC"));
			}
			
				
		}catch (SQLException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
	return fromVO;	

}
	public List<String> getdistinctTo(){
		Connection con=getConnection();
		List<String> toVO=new ArrayList<String>();
		String query="SELECT DISTINCT DEST FROM COSTDIS";
		try{
			Statement stmt=(Statement) con.createStatement();
			ResultSet set=stmt.executeQuery(query);
			while(set.next())
			{
				toVO.add(set.getString("DEST"));
			}
			
				
		}catch (SQLException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
	return toVO;	

}
public static void main(String args[]){
	List<String> FromVO=new Login().getdistinctFrom();
	List<String> ToVO=new Login().getdistinctTo();
	
	int count=FromVO.size();
	for(int i=0;i<count;i++)
	{
		System.out.println(FromVO.get(i));
	}
	int count1=ToVO.size();
	for(int i=0;i<count1;i++)
	{
		System.out.println(ToVO.get(i));
	}
}

}

..

[Sunil Sunny]

RequestDispatcher rd = request.getRequestDispatcher("/index.jsp"); Instead of this Try this


RequestDispatcher rd =getServletContext().getRequestDispatcher("/index.jsp");