Code Logic of when close the statement java - oracle

Question

Well always teach me this way of open and close connections from database, then i search more and more because this is very important for the performance of my application.
Here is my Class connection
public class Connection {
jdbc:oracle:thin:#//xxx.xx.x.xxx:xxxx/xxxxx.xxxxxx.xxxxx.xxx;
protected static Connection cn = null;
protected Connection getCn() {
return cn;
}
public static void setCn(Connection cn) {
Connection.cn = cn;
}
public ResultSet select(String sql) throws Exception {
ResultSet rs = null;
Statement st = null;
try {
st = this.getCn().createStatement();
rs = st.executeQuery(sql);
} catch (java.sql.SQLException e) {
throw e;
}
return rs;
}
public void insert(String sql) throws Exception {
Statement st = null;
try {
st = this.getCn().createStatement();
st.executeUpdate(sql);
} catch (java.sql.SQLException e) {
throw e;
}
}
public Connection connect() throws Exception {
try {
DriverManager.registerDriver(new oracle.jdbc.driver.OracleDriver());
setCn(DriverManager.getConnection(DBURL, "user", "password"));
} catch (java.sql.SQLException e) {
throw e;
}
return cn;
}
Well that was for my Connection Class, now here i have some others class that extends from my Connection class to bring me data from the DataBase.
public String checkMethod() throws Exception {
ResultSet rs;
String sql = "xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx";
try {
this.connect();
rs = this.select(sql);
while (rs.next()) {
//some data collect
}
rs.close(); //here is my dude because when may i can put the statement.close() line?
} catch (Exception e) {
throw e;
} finally {
this.cerrar();
}
return "success";
}
im using jsf and oracle, i think this snippet should be in my class Connection after the catch but generates me and error of the resulset is closed when i execute the method rs.next() and is logic because the statement must be close after the reading data of the resultSet, so how can i close the statement in my class Connection or in other place??? any suggestions? please help me
finally {
if (st != null) {
st.close();
}
}

Answer 1

A quick fix to the problem is:
finally {
try{ st.close(); }catch( Exception ex ) { /* do nothing*/ }
}
this prevents from throwing an error when something goes wrong with the statement in other places of the code ( st is null, st is closed etc.).
A more elegant solution might be creating a helper class with methods that close statements, resultsets etc. and hide exceptions that occur:
class DbCloser{
static void closeQuietly( Statement st ){
try{
st.close();
} catch( Exception ex ){
/* do nothing */
}
}
static void closeQuietly( ResultSet rs ){
try{
rs.close();
} catch( Exception ex ){
/* do nothing */
}
}
// .... etc.
}
and then use that helper class in finally blocks in code:
finally {
DbCloser.closeQuietly( st );
}
There is ready-made DbUtils package from Appache Commons that has already implemented such helper methods, just download this library and place it in the class-path, see this links for details:
http://commons.apache.org/proper/commons-dbutils/
http://commons.apache.org/proper/commons-dbutils/apidocs/index.html
And finally I would suggest to place close methods only in finnaly blocks:
try {
......
rs = this.select(sql);
.......
...........
// Do not close the statement here ......
// rs.close(); //here is my dude because when may i can put the statement.close() line?
} catch (Exception e) {
throw e;
} finally {
// ..... always close it here !!!
DbUtils.closeQuietly( st );
.........
}

Answer 2

i use this one
finally {
try{
if(st!=null){
st.close();
st=null;
}
}catch( Exception ex )
{
/* you can log this*/
}
}

Answer 3

Finally, I solved it like this:
public String checkMethod() throws Exception {
ResultSet rs;
String sql = "xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx";
try {
this.connect();
rs = this.select(sql);
while (rs.next()) {
//some data collect
}
rs.close();
rs.getStatement().close(); 'This works for me =)
} catch (Exception e) {
throw e;
} finally {
this.cerrar();
}
return "success";
}