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ExecuteQuery returns null while execute statement returns true

Here's my java Code trying to fetch a ResultSet from DB.
try{
ps=conn.prepareStatement(QueryMapper.SCHEDULE_APPLICANT_STATUS);
ps.setString(1,schedule_id);
rs1=ps.execute();
System.out.println(rs1);
ResultSet rs = null;
while(rs1)
{
rs=ps.executeQuery();
System.out.println(rs.next());
Application applicationBean= new Application();
System.out.println("ABC"+schedule_id);
applicationBean.setScheduledProgramId(rs.getString(3));
applicationBean.setStatus(rs.getString(2));
applicationBean.setApplicantId(rs.getString(1));
applicationList.add(applicationBean);
applicationCount++;
}
}catch (SQLException sqlException) {
log.error(sqlException.getMessage());
System.out.println(sqlException.getMessage());
}
When I try to run this, I'm not able to fetch the result set at rs using executeQuery statement. When I tried executing using execute statement it returned true which means some resultset is getting returned. Why is my executeQuery returning null.
The sql query I'm trying to run is
SELECT * FROM APPLICATION WHERE SCHEDULED_PROGRAM_ID=?
This query runs fine and fetch results when executed in sql manager.
Can you tell where I'm doing wrong.

In the code as shown, rs can only be null if rs1 is false, which can only be the case if you are executing something that does not produce a result set (or if your JDBC driver has a bug, but that is less likely).
What you're doing though, makes no sense. If you use execute(), then you should not execute your query again to obtain the result set. Doing that is inefficient, as you're asking the database server to redo the work it did for your first execute(), use getResultSet() instead. As documented on PreparedStatement.execute():
The execute method returns a boolean to indicate the form of the
first result. You must call either the method getResultSet or
getUpdateCount to retrieve the result; you must call
getMoreResults to move to any subsequent result(s).
However, if you know you are executing a query that produces a result set (and a select always produces a result set, even if it is empty!), then you should use executeQuery(). That simplifies your code.
Your code also has an infinite loop. Did you mean to use if (rs1) instead of while(rs1)?
You should change your code to something like
try (PreparedStatement ps=conn.prepareStatement(QueryMapper.SCHEDULE_APPLICANT_STATUS)) {
ps.setString(1,schedule_id);
try (ResultSet rs = ps.executeQuery()) {
// or maybe if (rs.next())?
while (rs.next()) {
Application applicationBean= new Application();
System.out.println("ABC"+schedule_id);
applicationBean.setScheduledProgramId(rs.getString(3));
applicationBean.setStatus(rs.getString(2));
applicationBean.setApplicantId(rs.getString(1));
applicationList.add(applicationBean);
applicationCount++;
}
}
} catch (SQLException sqlException) {
log.error(sqlException.getMessage());
System.out.println(sqlException.getMessage());
}

You don't need two ResultSet objects and you only need to execute the PreparedStatement once. The typical pattern is:
rs = ps.executeQuery();
while (rs.next()) {
// process the row returned by next()
// e.g.,
System.out.println(rs.getString(1));
}

You are missing your reader.
It must be something like: while(rs1.read())

How to check if entered value is equal to a value in a sql database

I have a database with 7 rows, and 4 columns in each. I am prompting a user to enter a code, and I need to cross reference the database to see if the entered code equals one of the codes in the database (first column in each row).
At first, I was checking if the result set came up as null, but that was not working. I was tryingif(rs.wasNull()) but it never seemed to execute.
Does anybody have any advice on what to look at to solve my issue? Here's a code snippet if helps at all.
if(!rs.wasNull()) {
while(rs.next()) {
Products temp = new Products(rs.getString(1), rs.getString(2), rs.getDouble(3), rs.getBoolean(4));
productsList.add(temp);
// For testing purposes
//out.println(temp.toString());
request.setAttribute("productsList", productsList);
request.getRequestDispatcher("Scan.jsp").forward(request, response);
}
}
else if(rs.wasNull()) {
Products wrongCode = null;
productsList.add(wrongCode);
request.setAttribute("productsList", productsList);
request.getRequestDispatcher("Scan.jsp").forward(request, response);
}
edit: I now know that ResultSet never returns null. It will return an empty ResultSet.
edit2: I've wrote this method to solve the problem:
public boolean codeExists(int code) {
final String SELECT_QUERY = "SELECT * FROM productcatalogue WHERE code = ?";
try {
PreparedStatement statement = conn.prepareStatement(SELECT_QUERY); // Create query statement
statement.setInt(1, code);
ResultSet queryResult = statement.executeQuery();
if (!queryResult.next()) { // Check if code entered exists
return false; // Tells that the author doesn't exist
}
} catch (SQLException sqlException) {
sqlException.printStackTrace();
}
return true; //Otherwise the item exists
}

If the result is empty it will never go into while loop. This is a condition which is used to separate code logic. Calling additional code on the result set is useless.
You should check the jdbc api for ResultSet#wasNull():
wasNull
boolean wasNull()
throws SQLException
Reports whether the last column read had a value of SQL NULL. Note that you must first call one of the getter methods on a column to try to read its value and then call the method wasNull to see if the value read was SQL NULL.
Returns:
true if the last column value read was SQL NULL and false otherwise
Throws:
SQLException - if a database access error occurs or this method is called on a closed result set

java.lang.NullPointerException ... Initializing the JDBC MYSQL connection

Please don't suggest me to use InternalFrame or Dialogs. I can't start the project from beginning.
Theme: I'm building a GUI program to display mark-sheet. I've taken 3 JFrames & 1 simple class...
Frame1.java
It's having 1 JTextField to enter roll_no. & 2 buttons to feedData in DB & showResult. feedData button calls Frame2 & showResult button calls Frame3.
Frame2.java
For feeding data have several JTextFields & Buttons that transfer content to mySQL DB.
Frame3.java
is a result window that fetches content from DB.
Support.java
Contains static variables & getter-setter methods for them
.....
.....//contains in Support.java
public boolean add() {
query = "Insert into table1 (enroll,Sname,Fname,sub1,sub2,sub3,sub4,sub5 )values(?,?,?,?,?)";
try {
PreparedStatement psmt = conn.prepareStatement(query);
psmt.setString(1, enroll);
psmt.setString(2, Sname);
psmt.setString(3, Fname);
psmt.setInt(4, sub1);
psmt.setInt(5, sub2);
psmt.setInt(6, sub3);
psmt.setInt(7, sub4);
psmt.setInt(8, sub5);
int y = 0;
y = psmt.executeUpdate();
if (y == 0) {
return false;
}
} catch (Exception e) {
e.printStackTrace();
return false;
}
return true;
}
add() is called on pressing save button in Frame2.java . . . If catch block is executing, why println(query) printing NULL

Based on some of your question tags and responses in the comments to other answers and on the question itself, I'm presuming that somewhere in your code, you intend to call
Class.forName("com.mysql.jdbc.Driver").newInstance();
conn = DriverManager.getConnection(url, username, password);
This is not happening before your add() method is called. In order to fix it, I'd recommend this (bulk of code borrowed from Vivek bhatnagar's answer):
try {
conn = DriverManager.getConnection(url, username, password);
PreparedStatement pstmt = conn.prepareStatement("INSERT INTO `table`
(pid,tid,rid,tspend,description) VALUE
(?,?,?,?,?)");
pstmt.setString(1, pid );
pstmt.setString(2, tid);
pstmt.setString(3, rid);
pstmt.setInt(4, tspent);
pstmt.setString(5,des );
pstmt.executeUpdate();
} catch (Exception e) {
// whatever you want to do to handle the exception
} finally {
// close your connection
}
If you're on Java 7, set up like this:
try (Connection conn = DriverManager.getConnection(url, username, password)) {
try (PreparedStatement pstmt = conn.prepareStatement(/*sql here*/)) {
// Your code here
} catch (SQLException sqle) {
// handle exceptions from the statement
}
} catch (SQLException outerSqlEx) {
// handle exceptions from connecting
}
How could I tell what your problem was (general help for NullPointerException)?
NullPointerException is only thrown when you try to call a method on a null variable (and at a few other specific times, as noted in the API documentation). The easy way to locate a NullPointerException is to look for the line the stack trace indicates, and then look for the dots on the line. There's only two lines in your try block that can throw a NullPointerException.
Statement stmt = conn.createStatement();
// could be here ----^
and
y = stmt.executeUpdate(query);
// or --^
So let's look at the dots. The first one will throw when conn is null. The second one will throw when stmt is null. In your original code, which you've now edited in response to the other answers, you set the value of query after you called conn.createStatement();. Since query was still null in your catch block, we know that it hadn't yet been set, and thus it must be the first one, so conn is null at that point in the program.
Furthermore, since the API Documentation for createStatement
implies that it will either return a valid Connection object or throw an SQLException, we can be pretty sure that stmt will never be null when executeUpdate is called.

In your try block, you are calling a method that is possible to throw an exception before setting the variable in question:
Statement stmt = conn.createStatement();
query = "Insert into table1 (enroll,Sname,Fname,sub1,sub2,sub3,sub4,sub5 )values('" + getEnroll() + "','" + getSname() + "','"+getFname()+"',"+getSub1()+","+getSub2()+","+getSub3()+","+getSub4()+","+getSub5()+")";
Therefore, if your code fails on the conn.createStatement() line, it will enter the catch block without the query variable being initialized.
You can fix this simply by switching the order of the statements, or by putting the query line outside and before the try/catch blocks.

Adding to what #Southpaw answered :
you can use something like this also :
PreparedStatement pstmt = con.prepareStatement("INSERT INTO `table`
(pid,tid,rid,tspend,description) VALUE
(?,?,?,?,?)");
pstmt.setString(1, pid );
pstmt.setString(2, tid);
pstmt.setString(3, rid);
pstmt.setInt(4, tspent);
pstmt.setString(5,des );
pstmt.executeUpdate();
Kindly Note its benefits:
1."Query is rewritten and compiled by the database server"
If you don't use a prepared statement, the database server will have to parse, and compute an execution plan for the statement each time you run it. If you find that you'll run the same statement multiple times (with different parameters) then its worth preparing the statement once and reusing that prepared statement. If you are querying the database adhoc then there is probably little benefit to this.
2."Protected against SQL injection"
This is an advantage you almost always want hence a good reason to use a PreparedStatement everytime. Its a consequence of having to parameterize the query but it does make running it a lot safer. The only time I can think of that this would not be useful is if you were allowing adhoc database queries; You might simply use the Statement object if you were prototyping the application and its quicker for you, or if the query contains no parameters.

Unable to get value from ResultSet

I am working on a web application using Java and MySQL.
I created a method that is supposed to return an ArrayList of the respective column name based on the various tables in the database.
However, when I debugged the method, I realised the while(rs.next()) causes an error. I used this site for reference, hence I am not sure what went wrong.
This is the code. Thanks.
// Returns the the all the columns in the table
public ArrayList getColumnName(String tableName) throws SQLException {
ResultSet rs = null;
List<String> columnName = new ArrayList<String>();
Statement st = null;
Connection con = null;
try {
// Get a connection from the connection factory
con = DriverManager.getConnection("jdbc:mysql://localhost:3306/information_schema", "root", "xxxx");
// Create a Statement object so we can submit SQL statements to the driver
st = con.createStatement();
StringBuilder sql = new StringBuilder("SELECT column_name FROM information_schema.columns " +
"WHERE table_schema = 'testDB' AND table_name = '");
sql.append(tableName).append("'");
rs = st.executeQuery(sql.toString());
while (rs.next()) { // getting error..
columnName.add(rs.getString("column_name"));
}
} catch (SQLException ex) {
Logger.getLogger(ModificationPage.class.getName()).log(Level.SEVERE, null, ex);
} finally {
if (con != null || st != null) {
st.close();
con.close();
}
}
return (ArrayList) columnName;
}

According to the Javadoc of 1.6 (not sure which version of Java you're using):
Throws:
SQLException - if a database access error occurs or this method is called on a closed result set
It's very, very unlikely that if you actually got to the line where rs.next() was called, that a database error occurred just then. So, the most likely result is that the result set was closed.
Please alter your code to the following and see if you still get the error on the same line:
while (!rs.isClosed() && rs.next()) { // getting error..
columnName.add(rs.getString("column_name"));
}
Also, Holy SQL Injection Attack, Batman!
Taking the raw string as you're doing and enclosing it within single quotes leads this code to have an SQL injection vulnerability. Basically all a malicious user has to do is end your query with a single quote (') and run a query of their own afterwards.

So, the exception never happens ?
A query error should be thrown at rs = st.executeQuery(sql.toString()) if that were the case, but if it make it to whileand didn't iterate, it's because of an empty resultset
Maybe you're passing wrong arguments to the query ?

How can I avoid ResultSet is closed exception in Java?

As soon as my code gets to my while(rs.next()) loop it produces the ResultSet is closed exception. What causes this exception and how can I correct for it?
EDIT: I notice in my code that I am nesting while(rs.next()) loop with another (rs2.next()), both result sets coming from the same DB, is this an issue?

Sounds like you executed another statement in the same connection before traversing the result set from the first statement. If you're nesting the processing of two result sets from the same database, you're doing something wrong. The combination of those sets should be done on the database side.

This could be caused by a number of reasons, including the driver you are using.
a) Some drivers do not allow nested statements. Depending if your driver supports JDBC 3.0 you should check the third parameter when creating the Statement object. For instance, I had the same problem with the JayBird driver to Firebird, but the code worked fine with the postgres driver. Then I added the third parameter to the createStatement method call and set it to ResultSet.HOLD_CURSORS_OVER_COMMIT, and the code started working fine for Firebird too.
static void testNestedRS() throws SQLException {
Connection con =null;
try {
// GET A CONNECTION
con = ConexionDesdeArchivo.obtenerConexion("examen-dest");
String sql1 = "select * from reportes_clasificacion";
Statement st1 = con.createStatement(
ResultSet.TYPE_SCROLL_INSENSITIVE,
ResultSet.CONCUR_READ_ONLY,
ResultSet.HOLD_CURSORS_OVER_COMMIT);
ResultSet rs1 = null;
try {
// EXECUTE THE FIRST QRY
rs1 = st1.executeQuery(sql1);
while (rs1.next()) {
// THIS LINE WILL BE PRINTED JUST ONCE ON
// SOME DRIVERS UNLESS YOU CREATE THE STATEMENT
// WITH 3 PARAMETERS USING
// ResultSet.HOLD_CURSORS_OVER_COMMIT
System.out.println("ST1 Row #: " + rs1.getRow());
String sql2 = "select * from reportes";
Statement st2 = con.createStatement(
ResultSet.TYPE_SCROLL_INSENSITIVE,
ResultSet.CONCUR_READ_ONLY);
// EXECUTE THE SECOND QRY. THIS CLOSES THE FIRST
// ResultSet ON SOME DRIVERS WITHOUT USING
// ResultSet.HOLD_CURSORS_OVER_COMMIT
st2.executeQuery(sql2);
st2.close();
}
} catch (SQLException e) {
e.printStackTrace();
} finally {
rs1.close();
st1.close();
}
} catch (SQLException e) {
} finally {
con.close();
}
}
b) There could be a bug in your code. Remember that you cannot reuse the Statement object, once you re-execute a query on the same statement object, all the opened resultsets associated with the statement are closed. Make sure you are not closing the statement.

Also, you can only have one result set open from each statement. So if you are iterating through two result sets at the same time, make sure they are executed on different statements. Opening a second result set on one statement will implicitly close the first.
http://java.sun.com/javase/6/docs/api/java/sql/Statement.html

The exception states that your result is closed. You should examine your code and look for all location where you issue a ResultSet.close() call. Also look for Statement.close() and Connection.close(). For sure, one of them gets called before rs.next() is called.

You may have closed either the Connection or Statement that made the ResultSet, which would lead to the ResultSet being closed as well.

Proper jdbc call should look something like:
try {
Connection conn;
Statement stmt;
ResultSet rs;
try {
conn = DriverManager.getConnection(myUrl,"","");
stmt = conn.createStatement();
rs = stmt.executeQuery(myQuery);
while ( rs.next() ) {
// process results
}
} catch (SqlException e) {
System.err.println("Got an exception! ");
System.err.println(e.getMessage());
} finally {
// you should release your resources here
if (rs != null) {
rs.close();
}
if (stmt != null) {
stmt.close();
}
if (conn != null) {
conn.close();
}
}
} catch (SqlException e) {
System.err.println("Got an exception! ");
System.err.println(e.getMessage());
}
you can close connection (or statement) only after you get result from result set. Safest way is to do it in finally block. However close() could also throe SqlException, hence the other try-catch block.

I got same error everything was correct only i was using same statement interface object to execute and update the database.
After separating i.e. using different objects of statement interface for updating and executing query i resolved this error. i.e. do get rid from this do not use same statement object for both updating and executing the query.

Check whether you have declared the method where this code is executing as static. If it is static there may be some other thread resetting the ResultSet.

make sure you have closed all your statments and resultsets before running rs.next. Finaly guarantees this
public boolean flowExists( Integer idStatusPrevious, Integer idStatus, Connection connection ) {
LogUtil.logRequestMethod();
PreparedStatement ps = null;
ResultSet rs = null;
try {
ps = connection.prepareStatement( Constants.SCRIPT_SELECT_FIND_FLOW_STATUS_BY_STATUS );
ps.setInt( 1, idStatusPrevious );
ps.setInt( 2, idStatus );
rs = ps.executeQuery();
Long count = 0L;
if ( rs != null ) {
while ( rs.next() ) {
count = rs.getLong( 1 );
break;
}
}
LogUtil.logSuccessMethod();
return count > 0L;
} catch ( Exception e ) {
String errorMsg = String
.format( Constants.ERROR_FINALIZED_METHOD, ( e.getMessage() != null ? e.getMessage() : "" ) );
LogUtil.logError( errorMsg, e );
throw new FatalException( errorMsg );
} finally {
rs.close();
ps.close();
}

A ResultSetClosedException could be thrown for two reasons.
1.) You have opened another connection to the database without closing all other connections.
2.) Your ResultSet may be returning no values. So when you try to access data from the ResultSet java will throw a ResultSetClosedException.

It happens also when using a ResultSet without being in a #Transactional method.
ScrollableResults results = getScrollableResults("select e from MyEntity e");
while (results.next()) {
...
}
results.close();
if MyEntity has eager relationships with other entities. the second time results.next() is invoked the ResultSet is closed exception is raised.
so if you use ScrollableResults on entities with eager relationships make sure your method is run transactionally.

"result set is closed" happened to me when using tag <collection> in MyBatis nested (one-to-many) xml <select> statement
A Spring solution could be to have a (Java) Spring #Service layer, where class/methods calling MyBatis select-collection statements are annotated with
#Transactional(propagation = Propagation.REQUIRED)
annotations being:
import org.springframework.transaction.annotation.Propagation;
import org.springframework.transaction.annotation.Transactional;
this solution does not require to set the following datasource properties (i.e., in JBoss EAP standalone*.xml):
<xa-datasource-property name="downgradeHoldCursorsUnderXa">**true**\</xa-datasource-property>
<xa-datasource-property name="resultSetHoldability">**1**</xa-datasource-property>