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query about resultset

how can i check that resultset object is null or not

[59 byte] By [rachna_arora82a] at [2007-11-26 13:34:16]

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# 1

hey Rachna,please use the next().......... infact many ways to do that.Thanks n RegardsNaveen MMessage was edited by: Novice_inJAVA

Novice_inJAVAa at 2007-7-7 22:15:39 >

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# 2

hi by ueing next how can i know resultset is null or not can i m directly using NULL but its not workingrachna

rachna_arora82a at 2007-7-7 22:15:39 >

# 3

hai u can use null to check that a result set object is null or notlike this ResultSet rs;if(rs==null)try thisbye

balaji.aspla at 2007-7-7 22:15:39 >

# 4

already tried its not working

rachna_arora82a at 2007-7-7 22:15:39 >

# 5

did not understand the question... Do you want to check if the resultset contains object or resultset is valid not-null object?

AjaySingh516a at 2007-7-7 22:15:39 >

# 6

i ant to know that resultset have records or not

rachna_arora82a at 2007-7-7 22:15:39 >

# 7

you can use:

if(result.next()) {

// Has record.

}

else {

// Doesn't have record.

}

AjaySingh516a at 2007-7-7 22:15:39 >

# 8

try

{

String ans1=(request.getParameter("R1"));

//String name=(request.getParameter("T2"));

Class.forName("sun.jdbc.odbc.JdbcOdbcDriver");

Connection con=DriverManager.getConnection("jdbc:odbc:exam","","");

PreparedStatement s;

ResultSet rs;

String value = (session.getValue("s1")).toString();

String name=(request.getParameter("T1"));

s=con.prepareStatement("select emailid from check where emailid=?");

s.setString(1,value);

rs=s.executeQuery();

if (rs.next())

{

out.println("already reg");

}

else

{

PreparedStatement st=con.prepareStatement("update check set ans1=? where name Like ?");

st.setString(1,ans1);

st.setString(2,value);

st.executeUpdate();

out.println(value);

}

}catch(Exception e)

{

out.println(e);

}

now my code is this and its showing null pointer exception

rachna_arora82a at 2007-7-7 22:15:39 >

# 9

Which line causing null pointer exception.

you should check/validate for the input parameter(s) null or not.

if(!(value == null || value.trim() == "" )){

// do your sql codes here

}else{

// print exception

}

cybervink2000a at 2007-7-7 22:15:39 >

# 10

Us e.printStackTrace() so you see the complete message.When you post code, please use[code] and [/code] tags as described in [url= http://forum.java.sun.com/help.jspa?sec=formatting ]Formatting tips[/url] on the message entry page. It makes it much easier to

mlka at 2007-7-7 22:15:39 >

# 11

where should i write thise.printStackTrace()

rachna_arora82a at 2007-7-7 22:15:39 >

# 12

This is the same as this thread: http://forum.java.sun.com/thread.jspa?threadID=5119246Urk, database access mixed in with JSPs. Nasty stuff. Throw it away, split the database access out.

mlka at 2007-7-7 22:15:39 >

# 13

Have added my comments inline, potential places where

NullPointerException can occur. run it and post the result.

try

{

String ans1=(request.getParameter("R1"));

//String name=(request.getParameter("T2"));

Class.forName("sun.jdbc.odbc.JdbcOdbcDriver");

Connection con=DriverManager.getConnection("jdbc:odbc:exam","","");

PreparedStatement s;

ResultSet rs;

String value = (session.getValue("s1")).toString(); //AJAY - column

value s1 may be null

String name=(request.getParameter("T1"));

s=con.prepareStatement("select emailid from check where emailid=?");

s.setString(1,value);

rs=s.executeQuery();

if (rs.next())

{

out.println("already reg");

}

else

{

PreparedStatement st=con.prepareStatement("update check set ans1=? where

name Like ?");

st.setString(1,ans1);

st.setString(2,value);

st.executeUpdate();

out.println(value);

}

}catch(Exception e)

{

e.printStackTrace(); // AJAY - will print out the source of error.

}

AjaySingh516a at 2007-7-7 22:15:39 >

# 14

now its not showing errornot even nullpointerexception and alsi not saving data in databasenot showing already reg

rachna_arora82a at 2007-7-7 22:15:39 >

# 15

mlk,hope rachna is new to java thats why rachna mixes the jdbc code with jsp. it may takes sometime to comeout.

cybervink2000a at 2007-7-21 15:52:40 >

# 16

sourround the code that you suspect using try{ } and in the corresponding catch block call e.printStackTrace()

AnjanReddya at 2007-7-21 15:52:40 >

# 17

ya true i m vb 6 developer and this is my first project in java

rachna_arora82a at 2007-7-21 15:52:40 >

# 18

call con.commit() after st.executeUpdate();

AjaySingh516a at 2007-7-21 15:52:40 >

# 19

If you're using Access as your database, your UPDATE won't show up until you close your resources properly. That means ResultSet, Statement, and Connection each closed in individual try/catch blocks in a finally block.

Externalize your connection parameters (e.g., driver, URL, etc.) Those can change, and you don't want to have to recompile your code to do it.

duffymoa at 2007-7-21 15:52:40 >

# 20

OMG, I hope this isn't in a JSP.If it is, move it into a Java class that you can test off line. JDBC code does not belong in JSPs.%

duffymoa at 2007-7-21 15:52:40 >

# 21

> mlk,> > hope rachna is new to java thats why rachna mixes the> jdbc code with jsp. it may takes sometime to comeout.Why get into that in the first place?

aniseeda at 2007-7-21 15:52:40 >

# 22

oki will seggregate the jdbc and jspbut how can i call a class file in jsp with import statementor wat

rachna_arora82a at 2007-7-21 15:52:40 >

# 23

> but how can i call a class file in jsp with import

> statement

It works the same way as in any class. You import the class, create an object and call methods on it. If you could add JDBC code directly in the JSP, I am pretty sure you could write the code with your custom class in the same manner (except that you achieve some simplicity by getting the JDBC code out from where it should not be).

aniseeda at 2007-7-21 15:52:40 >

# 24

> Which line causing null pointer exception.

> you should check/validate for the input parameter(s)

> null or not.

> like

> if(!(value == null || value.trim() == "" )){

> // do your sql codes here

> else{

> // print exception

Don't compare String values using ==.

(value.trim() == "")

should be:

(value.trim().length() == 0)

(value.trim().equals(""))

doremifasollatidoa at 2007-7-21 15:52:40 >

# 25

thanx allmy prob is solved now

rachna_arora82a at 2007-7-21 15:52:40 >

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