how to compare two strings using if condition inside jsp page?

Question

Jsp code:

<% 
String usermailid=(String)session.getAttribute("Username");
System.out.println("value of session==="+usermailid.equals("null"));
String empty=null;

if(usermailid.equals("null")) {   

%>                          



<% } 

else
{%>


<%}%>

output:

Apr 7, 2014 5:39:31 PM org.apache.catalina.core.StandardWrapperValve invoke
SEVERE: Servlet.service() for servlet jsp threw exception
java.lang.NullPointerException
    at org.apache.jsp.election_005fresults_jsp._jspService(election_005fresults_jsp.java:437)
    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:374)
    at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:342)
    at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:267)
    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:128)
    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:293)
    at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:849)
    at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:583)
    at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:454)
    at java.lang.Thread.run(Unknown Source)

In the above code i want to compare two strings.but when ever i comapare them i am getting null pointer exception when both the values are null and showing value as false?? so can anyone tell me what is the exact way of comparing two string???

Answer 1

Use simple check

if (usermailid != null)

Answer 2

if(usermailid!=null)

try this it will work.

 String x = null; 
 String x = "null";

both are different

Answer 3

how to compare two strings using if condition inside jsp page?

Answer

Do not write scriptlets <% %> in JSP, because scriptlets shouldn't be used in JSPs for more than a decade. Learn the JSP EL, the JSTL, and use servlet for the Java code. How to avoid Java Code in JSP-Files?

So, I am posting solution using EL syantax.

${!empty Username}

Here Username is directly referred from session scope. empty is operator which checks for null as well as empty.

You can use <c:if> or <c:when> for conditional check.

<c:if test="${!empty Username}">
      //Username is not null here
</c:if>

Useful links

• Expression Language oracle docs
• Tag if
• Tag choose
• Using JSTL
• Tag core

Answer 4

Here you are getting usermailid null and you are trying to compare with String "null". see null is nothing(null) but "null" is a String with null as text.

Answer 5

first remove this line:

System.out.println("value of session==="+usermailid.equals("null"));

u may simply write this:

if(null == usermailid) {
  // email id is null
} else {
  // proceed ur logic 
}