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Best way to use an SQL connection in Java

My question is similar to this one, but more specific.
I have multiple classes that execute queries against the same database. The problem is that the host may occasionally experience problems with the Internet connection, and my application must be designed against that knowledge.
So I cannot just create java.sql.Connection once, because it can break at any time. If a connection breaks while executing one of the queries - it's OK for me. The easiest way is to just create a new one in each query method:
public static Profile getProfileBySteamID(long userid) {
try (Connection connection = DriverManager.getConnection(Globals.dbConnection);
Statement st = connection.createStatement()) {
final ResultSet res = st.executeQuery("SELECT " +
"p_id, p_name, p_id_dis, p_uid, " +
"p_lastupd, p_lastservertime, p_roles " +
"FROM profiles WHERE p_uid='" + userid + "'");
if (!res.next())
throw new RuntimeException("No such profile");
long disID = res.getLong("p_id_dis");
String steamid = res.getString("p_uid");
return new Profile(steamid, disID);
} catch (SQLException e) {
throw new RuntimeException(e);
}
}
public static Profile getProfileByDisID(long userid) {
try (Connection connection = DriverManager.getConnection(Globals.dbConnection);
Statement st = connection.createStatement()) {
final ResultSet res = st.executeQuery("SELECT " +
"p_id, p_name, p_id_dis, p_uid, " +
"p_lastupd, p_lastservertime, p_roles " +
"FROM profiles WHERE p_id_dis='" + userid + "'");
if (!res.next())
throw new RuntimeException("No such profile");
long disID = res.getLong("p_id_dis");
String steamid = res.getString("p_uid");
return new Profile(steamid, disID);
} catch (SQLException e) {
throw new RuntimeException(e);
}
}
// ... and about 7 more methods like these
I'm OK with the possible performance issues (because these queries are executed not so frequently), but this is too much repeated code that is hard to extract to other private methods, and, you know, kinda looks ugly.
So my question is how to get that java.sql.Statement (or better - PreparedStatement) in as short expression as possible, and without the try-catch statements if possible. Maybe I should consider using ConnectionPool?
I'd like to get some examples of the solution, or links to source code examples of ConnectionPool with PreparedStatements usage or anything similar

Write a helper method which does the common code:
public class DBHelper {
public interface SqlFunction<T> {
T apply(Statement statement) throws SQLException;
}
public static <T> T withStatement(SqlFunction<T> task) {
try (Connection connection = DriverManager.getConnection(Globals.dbConnection);
Statement st = connection.createStatement()) {
return task.apply(st);
} catch (SQLException e) {
throw new RuntimeException(e);
}
}
public static void main(String[] args) {
Profile p = DBHelper.withStatement(st -> {
final ResultSet res = st.executeQuery("SELECT " +
"p_id, p_name, p_id_dis, p_uid, " +
"p_lastupd, p_lastservertime, p_roles " +
"FROM profiles WHERE p_id_dis='" + userid + "'");
if (!res.next())
throw new RuntimeException("No such profile");
long disID = res.getLong("p_id_dis");
String steamid = res.getString("p_uid");
return new Profile(steamid, disID);
});
}
}
By the way, you should be using PreparedStatement -- it handles escaping parameters, so it is both easier to use and safer against malicious SQL injection.
Using a connection pool, e.g. Hikari, is also a good idea in addition to the approach I suggest above. It will handle broken connections and reduce the overhead of making new connections. It will also allow you to limit the number of concurrent connections your application will use.

Try / Try-with-resources and Connection, Statement and ResultSet closing

I have recently having some discussions with my professor about how to handle the basic jdbc connection scheme. Suppose we want to execute two queries, this is what he proposes
public void doQueries() throws MyException{
Connection con = null;
try {
con = DriverManager.getConnection(dataSource);
PreparedStatement s1 = con.prepareStatement(updateSqlQuery);
PreparedStatement s2 = con.prepareStatement(selectSqlQuery);
// Set the parameters of the PreparedStatements and maybe do other things
s1.executeUpdate();
ResultSet rs = s2.executeQuery();
rs.close();
s2.close();
s1.close();
} catch (SQLException e) {
throw new MyException(e);
} finally {
try {
if (con != null) {
con.close();
}
} catch (SQLException e2) {
// Can't really do anything
}
}
}
I don't like this approach, and I have two questions about it:
1.A) I think that, if any exception is thrown where we do 'other things', or in the line rs.close() or s2.close() then s1 wouldn't have been closed when the method ends. Am I right about that?
1.B) The professor keeps asking me to explicitly close the ResultSet (even when the Statement documentation makes clear that it will close the ResultSet) She says that Sun recommends it. Is there any reason to do so?
Now this is what I think is the correct code for the same thing:
public void doQueries() throws MyException{
Connection con = null;
PreparedStatement s1 = null;
PreparedStatement s2 = null;
try {
con = DriverManager.getConnection(dataSource);
s1 = con.prepareStatement(updateSqlQuery);
s2 = con.prepareStatement(selectSqlQuery);
// Set the parameters of the PreparedStatements and maybe do other things
s1.executeUpdate();
ResultSet rs = s2.executeQuery();
} catch (SQLException e) {
throw new MyException(e);
} finally {
try {
if (s2 != null) {
s2.close();
}
} catch (SQLException e3) {
// Can't do nothing
}
try {
if (s1 != null) {
s1.close();
}
} catch (SQLException e3) {
// Can't do nothing
}
try {
if (con != null) {
con.close();
}
} catch (SQLException e2) {
// Can't do nothing
}
}
}
2.A) Is this code correct? (Is it guaranteed that all will be closed when the method ends?)
2.B) This is very large and verbose (and it gets worse if there are more Statements) Is there any shorter or more elegant way to do this without using try-with-resources?
Finally this is the code I like the most
public void doQueries() throws MyException{
try (Connection con = DriverManager.getConnection(dataSource);
PreparedStatement s1 = con.prepareStatement(updateSqlQuery);
PreparedStatement s2 = con.prepareStatement(selectSqlQuery))
{
// Set the parameters of the PreparedStatements and maybe do other things
s1.executeUpdate();
ResultSet rs = s2.executeQuery();
} catch (SQLException e) {
throw new MyException(e);
}
}
3) Is this code correct? I think my professor doesn't like this way because there is no explicit close of the ResultSet, but she has told me that she is fine with it as long as in the documentation it is clear that all is closed. Can you give any link to the official documentation with a similar example, or based in the documentation show that there is are no problems with this code?

tl;dr
In theory closing the statement closes the result set.
In practice, some faulty JDBC driver implementations failed to do so, notoriously. Thus the advice from your instructor that she learned from the School Of Hard Knocks.
Unless you are familiar with every implementation of every JDBC
driver that might be deployed for your app, use
try-with-resources to auto-close every level of your JDBC
work such as statements and result sets.
Use try-with-resources syntax
None of your code is fully using try-with-resources. In try-with-resources syntax, you declare and instantiate your Connection, PreparedStatement, and ResultSet in parentheses, before the braces. See Tutorial by Oracle.
While your ResultSet is not being explicitly closed in your last code example, it should be closed indirectly when its statement is closed. But as discussed below, it might not be closed because of faulty JDBC driver.
AutoCloseable
Any such objects implementing AutoCloseable will automatically have their close method invoked. So no need for those finally clauses.
How do you know which objects are auto-closable and which are not? Look at their class documentation to see if it declares AutoCloseable as a super-interface. Conversely, see the JavaDoc page for AutoCloseable for a list of all the bundled sub-interfaces and implementing classes (dozens actually).
For example, for SQL work, we see that Connection, Statement, PreparedStatement, ResultSet, and RowSet are all auto-closable but DataSource is not. This makes sense, as DataSource stores data about potential resources (database connections) but is not itself a resource. A DataSource is never “open” so no need to close.
See Oracle Tutorial, The try-with-resources Statement.
Code example
Your last code example is getting close to good, but should have wrapped ResultSet in a try-with-resources statement to get automatically closed.
To quote ResultSet JavaDoc:
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.
As your teacher has been suggesting, there have been serious flaws in some JDBC drivers that failed to live up to the promise of the JDBC spec to close the ResultSet when its Statement or PreparedStatement is closed. So many programmers make a habit of closing each ResultSet object explicitly.
This extra duty is easier now with the try-with-resources syntax. In real work you’ll likely have a try-else around all your AutoCloseable objects such as ResultSet anyways. So my own opinion is: Why not make it a try-with-resources + else? Does not hurt, makes your code more self-documenting about your intentions, and it might help if your code ever encounters one of those faulty JDBC drivers. The only cost is a pair of parens, assuming you’d have a try-catch-else in place anyways.
As stated in the Oracle Tutorial, multiple AutoCloseable objects declared together will be closed in reverse order, just as we would want.
Tip: The try-with-resources syntax allows an optional semicolon on the last declared resource item. I include the semicolon as a habit because it reads well to my eye, is consistent, and facilitates cut-and-paste editing. I include it on your PreparedStatement s2 line.
public void doQueries() throws MyException{
// First try-with-resources.
try ( Connection con = DriverManager.getConnection( dataSource ) ;
PreparedStatement s1 = con.prepareStatement( updateSqlQuery ) ;
PreparedStatement s2 = con.prepareStatement( selectSqlQuery ) ;
) {
… Set parameters of PreparedStatements, etc.
s1.executeUpdate() ;
// Second try-with-resources, nested within first.
try (
ResultSet rs = s2.executeQuery() ;
) {
… process ResultSet
} catch ( SQLException e2 ) {
… handle exception related to ResultSet.
}
} catch ( SQLException e ) {
… handle exception related to Connection or PreparedStatements.
}
}
I suppose there is a more elegant syntax for this kind of work that might be invented in a future programming language. But for now, we have try-with-resources, and I do use it happily. While try-with-resources is not perfectly elegant, it is a big improvement over the older syntax.
By the way, Oracle recommends using a DataSource implementation for getting connections rather than the DriverManager approach seen in your code. Using DataSource throughout your code makes it easier to switch drivers or switch to a connection pool. See if your JDBC driver provides an implementation of DataSource.
Update: Java 9
Now in Java 9 you can initialize the resources before the try-with-resources. See this article. This flexibility may be useful in some scenarios.

The fun thing about JDBC code is that you're coding to a spec where it's not always clear how compliant your implementation is. There are a lot of different databases and drivers and some drivers are better-behaved than others. That tends to make people err on the side of caution, recommending things like closing everything explicitly. You could be ok with closing only the connection here. Closing the resultSet just to be on the safe side is hard to argue with. You don't indicate what database or driver you're using here, i wouldn't want to hardcode in assumptions about the driver that might not be valid for some implementation.
Closing things in sequence does leave you open to problems where an exception can get thrown and cause some of the closes to be skipped. You're right to be concerned about that.
Be aware this is a toy example. Most real code uses a connection pool, where calling the close method doesn't actually close the connection, instead it returns the connection to the pool. So resources may not get closed once you use a pool. If you want to change this code to use a connection pool then you'll have to go back and close the statements at least.
Also if you're objecting to the verbosity of this, the answer to that is to hide the code in reusable utilities that use strategies, resultSet mappers, prepared statement setters, etc. This has all been done before, of course; you'll be on the road to reinventing Spring JDBC.
Speaking of which: Spring JDBC closes everything explicitly (probably because it needs to work with as many drivers as possible, and doesn't want to cause problems due to some driver's not being well-behaved).

This is what I find to be the best solution for handling resources like JDBC. This method provides an immutable function, by leveraging final variables, and only declaring and assigning those variables if they are needed, it is very CPU efficient, and guarantees in all cases, that all resources that are assigned and opened are closed regardless of the state of exceptions. The technique you are using leaves gaps that can result in resource leaks if not carefully implemented to address all scenarios. This technique does not allow for a resource leak provided the pattern is always followed:
1) assign resource
2) try
3) use resource
4) finally close resource
public void doQueries() throws MyException {
try {
final Connection con = DriverManager.getConnection(dataSource);
try {
final PreparedStatement s1 = con.prepareStatement(updateSqlQuery);
try {
// Set the parameters of the PreparedStatements and maybe do other things
s1.executeUpdate();
} finally {
try { s1.close(); } catch (SQLException e) {}
}
final PreparedStatement s2 = con.prepareStatement(selectSqlQuery);
try {
// Set the parameters of the PreparedStatements and maybe do other things
final ResultSet rs = s2.executeQuery();
try {
// Do something with rs
} finally {
try { rs.close(); } catch (SQLException e) {}
}
} finally {
try { s2.close(); } catch (SQLException e) {}
}
} finally {
try { con.close(); } catch (SQLException e) {}
}
} catch (SQLException e) {
throw new MyException(e);
}
}
With Java 7, you can leverage the new try -with-resources to simplify this even more: The new try -with-resources follows the above logic flow, in that it will guarantee all resources include in the with resources block that are assigned get closed. any exception thrown in the with resources block will the thrown, but those assigned resources will still be closed. This code is much simplified and looks like this:
public void doQueries() throws MyException {
try (
final Connection con = DriverManager.getConnection(dataSource);
final PreparedStatement s1 = con.prepareStatement(updateSqlQuery);
final PreparedStatement s2 = con.prepareStatement(selectSqlQuery);
final ResultSet rs = s2.executeQuery()) {
s1.executeUpdate();
// Do something with rs
} catch (SQLException e) {
throw new MyException(e);
}
}
[EDIT]: moved rs assignment into the resources block to show the simplest implementation. In practice, this simple solution does not really work, as this is not efficient. A connection should be reused, since establishing the connection is a very costly operation. Additionally, this simple example does not assign query parameters to the prepared statement. Care should be taken to handle these scenarios, as the the resource block should only include assignment statements. To depict this, I have also added another example
public void doQueries() throws MyException {
final String updateSqlQuery = "select ##servername";
final String selecSqlQuery = "select * from mytable where col1 = ? and col2 > ?";
final Object[] queryParams = {"somevalue", 1};
try (final Connection con = DriverManager.getConnection(dataSource);
final PreparedStatement s1 = newPreparedStatement(con, updateSqlQuery);
final PreparedStatement s2 = newPreparedStatement(con, selectSqlQuery, queryParams);
final ResultSet rs = s2.executeQuery()) {
s1.executeUpdate();
while (!rs.next()) {
// do something with the db record.
}
} catch (SQLException e) {
throw new MyException(e);
}
}
private static PreparedStatement newPreparedStatement(Connection con, String sql, Object... args) throws SQLException
{
final PreparedStatement stmt = con.prepareStatement(sql);
for (int i = 0; i < args.length; i++)
stmt.setObject(i, args[i]);
return stmt;
}

This is indeed the primary motivation for try-with-resources. See the Java tutorials as reference. Your professor is out-of-date. If you want to deal with the result set issue you can always enclose it in another try-with-resources statement.

You could make a util class to handle closing of these resources. i.e
FYI i just ignored SQLExceptions from trying to close resources in the util class, but you could as verywell log or collect and throw them once you are done closing the resources in the collection depending on your needs
public class DBUtil {
public static void closeConnections(Connection ...connections){
if(connections != null ){
for(Connection conn : connections){
if(conn != null){
try {
conn.close();
} catch (SQLException ignored) {
//ignored
}
}
}
}
}
public static void closeResultSets(ResultSet ...resultSets){
if(resultSets != null ){
for(ResultSet rs: resultSets){
if(rs != null){
try {
rs.close();
} catch (SQLException ignored) {
//ignored
}
}
}
}
}
public static void closeStatements(Statement ...statements){
if(statements != null){
for(Statement statement : statements){
if(statement != null){
try {
statement.close();
} catch (SQLException ignored) {
//ignored
}
}
}
}
}
}
and then just call it from you method:
public void doQueries() throws MyException {
Connection con = null;
try {
con = DriverManager.getConnection(dataSource);
PreparedStatement s1 = null;
PreparedStatement s2 = null;
try {
s1 = con.prepareStatement(updateSqlQuery);
s2 = con.prepareStatement(selectSqlQuery);
// Set the parameters of the PreparedStatements and maybe do other things
s1.executeUpdate();
ResultSet rs = null;
try {
rs = s2.executeQuery();
} finally {
DBUtil.closeResultSets(rs);
}
} finally {
DBUtil.closeStatements(s2, s1);
}
} catch (SQLException e) {
throw new MyException(e);
} finally {
DBUtil.closeConnections(con);
}
}

I prefer to let Java auto-close. So I do something like this when I have to set values for ResultSet.
try (Connection conn = DB.getConn();
PreparedStatement ps = conn.prepareStatement("SELECT * FROM x WHERE y = ?")
) {
ps.setString(1, "yValue");
try(ResultSet rs = ps.executeQuery()) {
while(rs.next()) {
...
}
}
} catch (SQLException e) {
e.printStackTrace(e);
...
}

Is it Ok to Pass ResultSet?

In my situation, I am querying a database for a specific return (in this case registration information based on a username).
//Build SQL String and Query Database.
if(formValid){
try {
SQL = "SELECT * FROM users WHERE username=? AND email=?";
Collections.addAll(fields, username, email);
results = services.DataService.getData(SQL, fields);
if (!results.next()){
errMessages.add("User account not found.");
} else {
user = new User();
user.fillUser(results); //Is it ok to pass ResultSet Around?
}
} catch (SQLException e) {
e.printStackTrace();
} finally {
services.DataService.closeDataObjects(); //Does this close the ResultSet I passed to fillUser?
}
}
So once I query the database, if a result is found I create a new User object and populate it with the data I received from the database. I used to do all of this directly in the method that I was pulling the resultset into, but I realized I was doing a lot of redundant coding throughout my project so I moved it all into one central method that lives in the actual User bean.
public void fillUser(ResultSet data) throws SQLException{
setUserId(data.getInt("id"));
setFirstName(data.getString("first_name"));
setLastName(data.getString("last_name"));
setUsername(data.getString("username"));
setType(data.getString("type"));
setEmail(data.getString("email"));
}
I have done a few tests and from what I can determine, because I close the original resultset in the finally block of the query, the resultset that I pass into the fillUser method also gets closed. Or am I wrong and am I seriously leaking data? This is actually the second time I pass a resultset (so its two instances of one) because the block I use to query my database is
public static ResultSet getData(String SQL, ArrayList fields) throws SQLException {
try{
connection = Database.getConnection();
preparedStatement = connection.prepareStatement(SQL);
for(int i=0; i<fields.size(); i++){
Integer num = i + 1;
Object item = fields.get(i);
if(item instanceof String){
preparedStatement.setString(num, (String) item); //Array item is String.
} else if (item instanceof Integer){
preparedStatement.setInt(num, (Integer) item); //Array item is Integer.
}
}
resultSet = preparedStatement.executeQuery();
return resultSet;
}finally{
}
}
All of these code snippets live in separate classes and are reused multiple times throughout my project. Is it ok to pass a resultset around like this, or should I be attempting another method? My goal is to reduce the codes redundancy, but i'm not sure if i'm going about it in a legal manner.

Technically, it's OK to pass result sets, as long as you are not serializing and passing it to a different JVM, and your JDBC connection and statement are still open.
However, it's probably a better software engineer and programming practice to have DB access layer that returns you the result set in a Java encoded way (a list of User in your example). That way, your code would be cleaner and you won't have to worry if the ResultSet is already opened, or you have to scroll it to the top, you name it...

As everyone before me said its a bad idea to pass the result set. If you are using Connection pool library like c3p0 then you can safely user CachedRowSet and its implementation CachedRowSetImpl. Using this you can close the connection. It will only use connection when required. Here is snippet from the java doc:
A CachedRowSet object is a disconnected rowset, which means that it makes use of a connection to its data source only briefly. It connects to its data source while it is reading data to populate itself with rows and again while it is propagating changes back to its underlying data source. The rest of the time, a CachedRowSet object is disconnected, including while its data is being modified. Being disconnected makes a RowSet object much leaner and therefore much easier to pass to another component. For example, a disconnected RowSet object can be serialized and passed over the wire to a thin client such as a personal digital assistant (PDA).
Here is the code snippet for querying and returning ResultSet:
public ResultSet getContent(String queryStr) {
Connection conn = null;
Statement stmt = null;
ResultSet resultSet = null;
CachedRowSetImpl crs = null;
try {
Connection conn = dataSource.getConnection();
stmt = conn.createStatement();
resultSet = stmt.executeQuery(queryStr);
crs = new CachedRowSetImpl();
crs.populate(resultSet);
} catch (SQLException e) {
throw new IllegalStateException("Unable to execute query: " + queryStr, e);
}finally {
try {
if (resultSet != null) {
resultSet.close();
}
if (stmt != null) {
stmt.close();
}
if (conn != null) {
conn.close();
}
} catch (SQLException e) {
LOGGER.error("Ignored", e);
}
}
return crs;
}
Here is the snippet for creating data source using c3p0:
ComboPooledDataSource cpds = new ComboPooledDataSource();
try {
cpds.setDriverClass("<driver class>"); //loads the jdbc driver
} catch (PropertyVetoException e) {
e.printStackTrace();
return;
}
cpds.setJdbcUrl("jdbc:<url>");
cpds.setMinPoolSize(5);
cpds.setAcquireIncrement(5);
cpds.setMaxPoolSize(20);
javax.sql.DataSource dataSource = cpds;

delete sql not deleting

I'm trying to delete an event from my table. However I can't seem to get it to work.
My SQL statement is:
public void deleteEvent(String eventName){
String query = "DELETE FROM `Event` WHERE `eventName` ='"+eventName+"' LIMIT 1";
db.update(query);
System.out.println (query);
}
Using MySQL db

Try using the following :
String query = "DELETE FROM `Event` WHERE `eventName` ='"+eventName+"' LIMIT 1";
try {
Connection con = getConnection();
Statement s = con.createStatement();
s.execute(query);
} catch (Exception ex) {
ex.printStackTrace();
}
You have to code your getConnection() method to return a valid Database Connection.

I would suggest using Statement.executeUpdate method, since it returns an integer. So after performing this delete query you will also have information if you really deleted any records (in this case you would expect this method to return 1, since you are using LIMIT=1). I would also suggest closing Statement as soon as you don't need it, here is skeleton implementation:
private void performDelete(Connection conn, String deleteQuery, int expectedResult) throws SQLException {
Statement stmt = conn.createStatement();
int result = -1;
try {
result = stmt.executeUpdate(deleteQuery);
if(result != expectedResult) {
//Here you can check the result. Perhaps you don't need this part
throw new IllegalStateException("Develete query did not return expected value");
}
} catch(SQLException e) {
//Good practice if you use loggers - log it here and rethrow upper.
//Or perhaps you don't need to bother in upper layer if the operation
//was successful or not - in such case, just log it and thats it.
throw e;
} finally {
//This should be always used in conjunction with ReultSets.
//It is not 100% necessary here, but it will not hurt
stmt.close();
}
}

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>