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Getting wrong output in PreparedStatement [duplicate]

This question already has answers here:
mysql prepared statement error: MySQLSyntaxErrorException
(2 answers)
Closed 6 years ago.
I've a course table with the columns,
id, teacher_id and name.
This is the method that I'm using to get a course by id.
public static Course getById(int id) throws SQLException {
String query = "SELECT * FROM courses WHERE id = ?" ;
Course course = new Course();
Connection connection = null;
PreparedStatement statement = null;
ResultSet resultSet = null;
try{
DriverManager.registerDriver(new com.mysql.jdbc.Driver ());
connection = (Connection) DriverManager.getConnection(ConnectDb.CONN_STRING, ConnectDb.USERNAME, ConnectDb.PASSWORD);
statement = (PreparedStatement) connection.prepareStatement(query, ResultSet.TYPE_SCROLL_INSENSITIVE,
ResultSet.CONCUR_READ_ONLY);
statement.setInt(1, id);
resultSet = statement.executeQuery(query);
while (resultSet.next()) {
course.setId(resultSet.getInt("id"));
course.setName(resultSet.getString("name"));
course.setTeacherId(resultSet.getInt("teacher_id"));
}
}catch (SQLException e) {
System.err.println(e);
}finally{
if (resultSet != null) resultSet.close();;
if (statement != null) statement.close();
if(connection != null) connection.close();
}
return course;
}// end of method
When I run this method, I get an output id :0, teacher_id : 0
The server log says that I've an SQLException
com.mysql.jdbc.exceptions.jdbc4.MySQLSyntaxErrorException: You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near '?' at line 1

The bug is here:
resultSet = statement.executeQuery(query);
You're not calling PreparedStatement#executeQuery, you're calling Statement#executeQuery (Statement is a superinterface of PreparedStatement). So the parameter substitution isn't happening and you're actually sending that ? to the server.
Change it to:
resultSet = statement.executeQuery();
// No argument here ---------------^
(And yes, this is an API design flaw; and no, you're not the first to fall into it.)
There are a few other things about that code that could use improvement:
You're always returning a Course, even if an exception occurred. Best practices would be to allow the exception to propagate to the caller; second-best practices would be to return some kind of flag to the caller that an error occurred, such as null.
The try-with-resources statement can make that code both shorter and clearer
You shouldn't have to cast the return values of getConnection or prepareStatement.
You're using while, but you're expecting only a single result. if would make more sense.
On that topic, you can give the driver a hint in that regard by using setMaxRows.
Your method declares that it can throw SQLException, which is literally true since it calls close, but the only useful SQLException is actually being caught, logged, and suppressed by the code, making declaring it on the method a bit misleading.
I'm told modern JDBC drivers don't need the registerDriver call anymore. (I personally haven't used JDBC for a while now, so...)
Here's an example incoporating the above. It allows an exception to propagate, so errors (exceptional conditions) are not handled in the normal flow of code; it returns null if there's no matching course:
public static Course getById(int id) throws SQLException {
String query = "SELECT * FROM courses WHERE id = ?";
try (
Connection connection = DriverManager.getConnection(ConnectDb.CONN_STRING, ConnectDb.USERNAME, ConnectDb.PASSWORD);
PreparedStatement statement = connection.prepareStatement(query, ResultSet.TYPE_SCROLL_INSENSITIVE, ResultSet.CONCUR_READ_ONLY);
) {
statement.setInt(1, id);
statement.setMaxRows(1);
try (
ResultSet resultSet = statement.executeQuery();
) {
if (resultSet.next()) {
Course course = new Course();
course.setId(resultSet.getInt("id"));
course.setName(resultSet.getString("name"));
course.setTeacherId(resultSet.getInt("teacher_id"));
return course;
}
// No matching course
return null;
}
}
} // end of method
That can probably be improved further, but you get the idea.

Multiple ResultSets, different queries, same database SQLSERVER

Using JDBC driver, how can I use multiple result sets from different queries without continually opening and closing the connections, as it stand im extracting w.e I need and passing it to another method. Each time opening a new conn,statement and resultset
public static void OppQuery() {
Connection conn = null;
Statement stmt = null;
ResultSet result_set = null;
try {
Class.forName(JDBC_DRIVER);
conn = DriverManager.getConnection(DB_URL);
stmt = conn.createStatement();
String emailInfoQuery = "FROM WHERE";
}
public static void addQuery(String latestRenewalId) {
Connection conn = null;
Statement stmt = null;
ResultSet result_set = null;
try {
Class.forName(JDBC_DRIVER);
conn = DriverManager.getConnection(DB_URL);
stmt = conn.createStatement();
String new_AddressLine1, new_AddressLine2;
new_AddressLine1=new_AddressLine2="";
int new_ChannelOption= 0;
}
I tried to use multiple result sets in one method but it kept throwing exceptions saying the result set was closed. I don't have much experience with SqlServver so any guidance would help :-)

In JDBC, when the connection is in auto-commit mode (which is the default), any execution of a statement will commit the previous transaction and close any open result sets on the same connection (assuming the holdability is ResultSet.CLOSE_CURSORS_AT_COMMIT, which actually isn't the default for SQL Server). When you need to have multiple result sets open, you need to have auto-commit disabled (or use ResultSet.HOLD_CURSORS_OVER_COMMIT) and you need to use multiple Statement objects. JDBC requires that a new execute on the same Statement object closes any other open result sets from that same statement.
So
Disable auto-commit (Connection.setAutoCommit(false))
Use multiple Statement objects to open the ResultSets

Further to Mark's answer, since the Microsoft SQL Server JDBC driver seems to create "Holdable" ResultSet objects by default, the following test code does work when AutoCommit is enabled:
import java.sql.*;
public class SqlServerTest {
public static void main(String[] args) {
try {
String connectionUrl =
"jdbc:sqlserver://localhost:52865;" +
"databaseName=myDb;" +
"integratedSecurity=true";
Connection con = DriverManager.getConnection(connectionUrl);
System.out.println(String.format("con.getAutoCommit returned %s", con.getAutoCommit()));
Statement st1 = con.createStatement();
ResultSet rs1 = st1.executeQuery("SELECT id FROM odds");
rs1.next();
System.out.println(String.format("value from rs1: %d", rs1.getInt(1)));
Statement st2 = con.createStatement();
ResultSet rs2 = st2.executeQuery("SELECT id FROM evens");
rs2.next();
System.out.println(String.format("value from rs2: %d", rs2.getInt(1)));
rs1.next();
System.out.println(String.format("value from rs1: %d", rs1.getInt(1)));
rs2.next();
System.out.println(String.format("value from rs2: %d", rs2.getInt(1)));
rs2.close();
rs1.close();
con.close();
} catch(Exception e) {
e.printStackTrace();
}
}
}
For test data in tables named [odds]...
id description
-- -----------
1 one
3 three
5 five
...and [evens]...
id description
-- -----------
2 two
4 four
6 six
...the console output is:
con.getAutoCommit returned true
value from rs1: 1
value from rs2: 2
value from rs1: 3
value from rs2: 4

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 ?

Getting java.sql.SQLException: Operation not allowed after ResultSet closed

When I execute the following code, I get an exception. I think it is because I'm preparing in new statement with he same connection object. How should I rewrite this so that I can create a prepared statement AND get to use rs2? Do I have to create a new connection object even if the connection is to the same DB?
try
{
//Get some stuff
String name = "";
String sql = "SELECT `name` FROM `user` WHERE `id` = " + userId + " LIMIT 1;";
ResultSet rs = statement.executeQuery(sql);
if(rs.next())
{
name = rs.getString("name");
}
String sql2 = "SELECT `id` FROM `profiles` WHERE `id` =" + profId + ";";
ResultSet rs2 = statement.executeQuery(sql2);
String updateSql = "INSERT INTO `blah`............";
PreparedStatement pst = (PreparedStatement)connection.prepareStatement(updateSql);
while(rs2.next())
{
int id = rs2.getInt("id");
int stuff = getStuff(id);
pst.setInt(1, stuff);
pst.addBatch();
}
pst.executeBatch();
}
catch (Exception e)
{
e.printStackTrace();
}
private int getStuff(int id)
{
try
{
String sql = "SELECT ......;";
ResultSet rs = statement.executeQuery(sql);
if(rs.next())
{
return rs.getInt("something");
}
return -1;
}//code continues

The problem is with the way you fetch data in getStuff(). Each time you visit getStuff() you obtain a fresh ResultSet but you don't close it.
This violates the expectation of the Statement class (see here - http://docs.oracle.com/javase/7/docs/api/java/sql/Statement.html):
By default, only one ResultSet object per Statement object can be open at the same time. Therefore, if the reading of one ResultSet object is interleaved with the reading of another, each must have been generated by different Statement objects. All execution methods in the Statement interface implicitly close a statment's current ResultSet object if an open one exists.
What makes things even worse is the rs from the calling code. It is also derived off-of the statement field but it is not closed.
Bottom line: you have several ResultSet pertaining to the same Statement object concurrently opened.

A ResultSet object is automatically
closed when the Statement object that
generated it is closed, re-executed,
or used to retrieve the next result
from a sequence of multiple results.
I guess after while(rs2.next()) you are trying to access something from rs1. But it's already closed since you reexecuted statement to get rs2 from it. Since you didn't close it, I beleive it's used again below.

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>