I'm trying to implement Transactions for a script but I've run into a strange issue.
When I attempt to run a Prepared SQL Statement inside of a Transaction it is failing because it says that it needs a Transaction when the connection is assigned.
How does this work with Prepared Statements though because I intend to have multiple Transactions all using the same Prepared Statements.
My code is as follows
class dbTest {
public static SqlConnection db;
public static SqlCommand query;
static void Main(string[] args) {
db = connect();
prepare();
transaction01();
transaction02();
transaction03();
}
public static void prepare() {
query = new SqlCommand("select id from table where id = 1 for update", db);
query.Prepare();
}
public static void transaction01() {
SqlTransaction trans = db.BeginTransaction("Trn01");
SqlDataReader result = query.ExecuteReader();
while(result.Read()) { Console.WriteLine(result["id"]); }
result.Close();
trans.Commit();
}
public static void transaction02() {
SqlTransaction trans = db.BeginTransaction("Trn02");
SqlDataReader result = query.ExecuteReader();
while(result.Read()) { Console.WriteLine(result["id"]); }
result.Close();
trans.Commit();
}
public static void transaction03() {
SqlTransaction trans = db.BeginTransaction("Trn03");
SqlDataReader result = query.ExecuteReader();
while(result.Read()) { Console.WriteLine(result["id"]); }
result.Close();
trans.Commit();
}
}
How do I assign the Transaction to an existing Prepared Statement?
UPDATE
Changed the above code to better show the issue. The SQL is prepared once but I will be using it for multiple Transactions (or at least I want to)
UPDATE AGAIN
I have marked an answer below as the correct one because it looks like the best way to achieve this but for my needs in this very small example using query.Transaction got it working
public static void transaction01() {
SqlTransaction trans = db.BeginTransaction("Trn01");
query.Transaction = trans; // this line fixed it
SqlDataReader result = query.ExecuteReader();
while(result.Read()) { Console.WriteLine(result["id"]); }
result.Close();
trans.Commit();
}
When working with the SqlTransaction, you must set the SqlCommand.Transaction explicitly, even though enlisting in the current transaction is not optional in SQL Server.
select ... for update is not valid SQL Server syntax, instead use UPDLOCK to read a table and retain a restrictive lock for the duration of the transaction. EG
select id from table with (updlock) where id = 1
When I attempt to run a Prepared SQL Statement
It's rarely useful to use prepared statements with SQL Server. Query plan caching happens automatically even without it, and it really just reduces the size of the request on the network when you are executing a SqlCommand many times with differing parameters.
But a prepared SqlCommand is still bound to a single SqlConnection, which typically has a short lifetime, minimizing the potential benefits of preparing the SqlCommand.
You need to set the SqlCommand.Transaction to your transaction object.
it is not necessary with SQL Server to prepare the statement. Just keep executing.
Note also, as you can see in this post, that you must correctly dispose all DB objects.
Here is your code cleaned up:
class dbTest {
// DO NOT cache connection object
static void Main(string[] args) {
using(var db = connect())
using(var comm = GetCommand(db))
{
transaction01(comm);
transaction02(comm);
transaction03(comm);
}
}
public static SqlCommand GetCommand(SqlConnection conn) {
return new SqlCommand("select id from table with (updlock) where id = 1", conn);
}
public static void transaction01(SqlCommand comm) {
using(SqlTransaction trans = comm.Connection.BeginTransaction("Trn01"))
{
comm.Transaction = trans;
using(SqlDataReader result = query.ExecuteReader())
while(result.Read()) { Console.WriteLine(result["id"]); }
trans.Commit();
} // no need to close, using will sort that out
}
public static void transaction02(SqlCommand comm) {
using(SqlTransaction trans = comm.Connection.BeginTransaction("Trn02"))
{
comm.Transaction = trans;
using(SqlDataReader result = query.ExecuteReader())
while(result.Read()) { Console.WriteLine(result["id"]); }
trans.Commit();
} // no need to close, using will sort that out
}
public static void transaction03(SqlCommand comm) {
using(SqlTransaction trans = comm.Connection.BeginTransaction("Trn03"))
{
comm.Transaction = trans;
using(SqlDataReader result = query.ExecuteReader())
while(result.Read()) { Console.WriteLine(result["id"]); }
trans.Commit();
} // no need to close, using will sort that out
}
}
I want to INSERT a record in a database (which is Microsoft SQL Server in my case) using JDBC in Java. At the same time, I want to obtain the insert ID. How can I achieve this using JDBC API?
If it is an auto generated key, then you can use Statement#getGeneratedKeys() for this. You need to call it on the same Statement as the one being used for the INSERT. You first need to create the statement using Statement.RETURN_GENERATED_KEYS to notify the JDBC driver to return the keys.
Here's a basic example:
public void create(User user) throws SQLException {
try (
Connection connection = dataSource.getConnection();
PreparedStatement statement = connection.prepareStatement(SQL_INSERT,
Statement.RETURN_GENERATED_KEYS);
) {
statement.setString(1, user.getName());
statement.setString(2, user.getPassword());
statement.setString(3, user.getEmail());
// ...
int affectedRows = statement.executeUpdate();
if (affectedRows == 0) {
throw new SQLException("Creating user failed, no rows affected.");
}
try (ResultSet generatedKeys = statement.getGeneratedKeys()) {
if (generatedKeys.next()) {
user.setId(generatedKeys.getLong(1));
}
else {
throw new SQLException("Creating user failed, no ID obtained.");
}
}
}
}
Note that you're dependent on the JDBC driver as to whether it works. Currently, most of the last versions will work, but if I am correct, Oracle JDBC driver is still somewhat troublesome with this. MySQL and DB2 already supported it for ages. PostgreSQL started to support it not long ago. I can't comment about MSSQL as I've never used it.
For Oracle, you can invoke a CallableStatement with a RETURNING clause or a SELECT CURRVAL(sequencename) (or whatever DB-specific syntax to do so) directly after the INSERT in the same transaction to obtain the last generated key. See also this answer.
Create Generated Column
String generatedColumns[] = { "ID" };
Pass this geneated Column to your statement
PreparedStatement stmtInsert = conn.prepareStatement(insertSQL, generatedColumns);
Use ResultSet object to fetch the GeneratedKeys on Statement
ResultSet rs = stmtInsert.getGeneratedKeys();
if (rs.next()) {
long id = rs.getLong(1);
System.out.println("Inserted ID -" + id); // display inserted record
}
When encountering an 'Unsupported feature' error while using Statement.RETURN_GENERATED_KEYS, try this:
String[] returnId = { "BATCHID" };
String sql = "INSERT INTO BATCH (BATCHNAME) VALUES ('aaaaaaa')";
PreparedStatement statement = connection.prepareStatement(sql, returnId);
int affectedRows = statement.executeUpdate();
if (affectedRows == 0) {
throw new SQLException("Creating user failed, no rows affected.");
}
try (ResultSet rs = statement.getGeneratedKeys()) {
if (rs.next()) {
System.out.println(rs.getInt(1));
}
rs.close();
}
Where BATCHID is the auto generated id.
I'm hitting Microsoft SQL Server 2008 R2 from a single-threaded JDBC-based application and pulling back the last ID without using the RETURN_GENERATED_KEYS property or any PreparedStatement. Looks something like this:
private int insertQueryReturnInt(String SQLQy) {
ResultSet generatedKeys = null;
int generatedKey = -1;
try {
Statement statement = conn.createStatement();
statement.execute(SQLQy);
} catch (Exception e) {
errorDescription = "Failed to insert SQL query: " + SQLQy + "( " + e.toString() + ")";
return -1;
}
try {
generatedKey = Integer.parseInt(readOneValue("SELECT ##IDENTITY"));
} catch (Exception e) {
errorDescription = "Failed to get ID of just-inserted SQL query: " + SQLQy + "( " + e.toString() + ")";
return -1;
}
return generatedKey;
}
This blog post nicely isolates three main SQL Server "last ID" options:
http://msjawahar.wordpress.com/2008/01/25/how-to-find-the-last-identity-value-inserted-in-the-sql-server/ - haven't needed the other two yet.
Instead of a comment, I just want to answer post.
Interface java.sql.PreparedStatement
columnIndexes « You can use prepareStatement function that accepts columnIndexes and SQL statement.
Where columnIndexes allowed constant flags are Statement.RETURN_GENERATED_KEYS1 or Statement.NO_GENERATED_KEYS[2], SQL statement that may contain one or more '?' IN parameter placeholders.
SYNTAX «
Connection.prepareStatement(String sql, int autoGeneratedKeys)
Connection.prepareStatement(String sql, int[] columnIndexes)
Example:
PreparedStatement pstmt =
conn.prepareStatement( insertSQL, Statement.RETURN_GENERATED_KEYS );
columnNames « List out the columnNames like 'id', 'uniqueID', .... in the target table that contain the auto-generated keys that should be returned. The driver will ignore them if the SQL statement is not an INSERT statement.
SYNTAX «
Connection.prepareStatement(String sql, String[] columnNames)
Example:
String columnNames[] = new String[] { "id" };
PreparedStatement pstmt = conn.prepareStatement( insertSQL, columnNames );
Full Example:
public static void insertAutoIncrement_SQL(String UserName, String Language, String Message) {
String DB_URL = "jdbc:mysql://localhost:3306/test", DB_User = "root", DB_Password = "";
String insertSQL = "INSERT INTO `unicodeinfo`( `UserName`, `Language`, `Message`) VALUES (?,?,?)";
//"INSERT INTO `unicodeinfo`(`id`, `UserName`, `Language`, `Message`) VALUES (?,?,?,?)";
int primkey = 0 ;
try {
Class.forName("com.mysql.jdbc.Driver").newInstance();
Connection conn = DriverManager.getConnection(DB_URL, DB_User, DB_Password);
String columnNames[] = new String[] { "id" };
PreparedStatement pstmt = conn.prepareStatement( insertSQL, columnNames );
pstmt.setString(1, UserName );
pstmt.setString(2, Language );
pstmt.setString(3, Message );
if (pstmt.executeUpdate() > 0) {
// Retrieves any auto-generated keys created as a result of executing this Statement object
java.sql.ResultSet generatedKeys = pstmt.getGeneratedKeys();
if ( generatedKeys.next() ) {
primkey = generatedKeys.getInt(1);
}
}
System.out.println("Record updated with id = "+primkey);
} catch (InstantiationException | IllegalAccessException | ClassNotFoundException | SQLException e) {
e.printStackTrace();
}
}
I'm using SQLServer 2008, but I have a development limitation: I cannot use a new driver for it, I have to use "com.microsoft.jdbc.sqlserver.SQLServerDriver" (I cannot use "com.microsoft.sqlserver.jdbc.SQLServerDriver").
That's why the solution conn.prepareStatement(sql, Statement.RETURN_GENERATED_KEYS) threw a java.lang.AbstractMethodError for me.
In this situation, a possible solution I found is the old one suggested by Microsoft:
How To Retrieve ##IDENTITY Value Using JDBC
import java.sql.*;
import java.io.*;
public class IdentitySample
{
public static void main(String args[])
{
try
{
String URL = "jdbc:microsoft:sqlserver://yourServer:1433;databasename=pubs";
String userName = "yourUser";
String password = "yourPassword";
System.out.println( "Trying to connect to: " + URL);
//Register JDBC Driver
Class.forName("com.microsoft.jdbc.sqlserver.SQLServerDriver").newInstance();
//Connect to SQL Server
Connection con = null;
con = DriverManager.getConnection(URL,userName,password);
System.out.println("Successfully connected to server");
//Create statement and Execute using either a stored procecure or batch statement
CallableStatement callstmt = null;
callstmt = con.prepareCall("INSERT INTO myIdentTable (col2) VALUES (?);SELECT ##IDENTITY");
callstmt.setString(1, "testInputBatch");
System.out.println("Batch statement successfully executed");
callstmt.execute();
int iUpdCount = callstmt.getUpdateCount();
boolean bMoreResults = true;
ResultSet rs = null;
int myIdentVal = -1; //to store the ##IDENTITY
//While there are still more results or update counts
//available, continue processing resultsets
while (bMoreResults || iUpdCount!=-1)
{
//NOTE: in order for output parameters to be available,
//all resultsets must be processed
rs = callstmt.getResultSet();
//if rs is not null, we know we can get the results from the SELECT ##IDENTITY
if (rs != null)
{
rs.next();
myIdentVal = rs.getInt(1);
}
//Do something with the results here (not shown)
//get the next resultset, if there is one
//this call also implicitly closes the previously obtained ResultSet
bMoreResults = callstmt.getMoreResults();
iUpdCount = callstmt.getUpdateCount();
}
System.out.println( "##IDENTITY is: " + myIdentVal);
//Close statement and connection
callstmt.close();
con.close();
}
catch (Exception ex)
{
ex.printStackTrace();
}
try
{
System.out.println("Press any key to quit...");
System.in.read();
}
catch (Exception e)
{
}
}
}
This solution worked for me!
I hope this helps!
You can use following java code to get new inserted id.
ps = con.prepareStatement(query, Statement.RETURN_GENERATED_KEYS);
ps.setInt(1, quizid);
ps.setInt(2, userid);
ps.executeUpdate();
ResultSet rs = ps.getGeneratedKeys();
if (rs.next()) {
lastInsertId = rs.getInt(1);
}
It is possible to use it with normal Statement's as well (not just PreparedStatement)
Statement statement = conn.createStatement();
int updateCount = statement.executeUpdate("insert into x...)", Statement.RETURN_GENERATED_KEYS);
try (ResultSet generatedKeys = statement.getGeneratedKeys()) {
if (generatedKeys.next()) {
return generatedKeys.getLong(1);
}
else {
throw new SQLException("Creating failed, no ID obtained.");
}
}
Most others have suggested to use JDBC API for this, but personally, I find it quite painful to do with most drivers. When in fact, you can just use a native T-SQL feature, the OUTPUT clause:
try (
Statement s = c.createStatement();
ResultSet rs = s.executeQuery(
"""
INSERT INTO t (a, b)
OUTPUT id
VALUES (1, 2)
"""
);
) {
while (rs.next())
System.out.println("ID = " + rs.getLong(1));
}
This is the simplest solution for SQL Server as well as a few other SQL dialects (e.g. Firebird, MariaDB, PostgreSQL, where you'd use RETURNING instead of OUTPUT).
I've blogged about this topic more in detail here.
With Hibernate's NativeQuery, you need to return a ResultList instead of a SingleResult, because Hibernate modifies a native query
INSERT INTO bla (a,b) VALUES (2,3) RETURNING id
like
INSERT INTO bla (a,b) VALUES (2,3) RETURNING id LIMIT 1
if you try to get a single result, which causes most databases (at least PostgreSQL) to throw a syntax error. Afterwards, you may fetch the resulting id from the list (which usually contains exactly one item).
In my case ->
ConnectionClass objConnectionClass=new ConnectionClass();
con=objConnectionClass.getDataBaseConnection();
pstmtGetAdd=con.prepareStatement(SQL_INSERT_ADDRESS_QUERY,Statement.RETURN_GENERATED_KEYS);
pstmtGetAdd.setString(1, objRegisterVO.getAddress());
pstmtGetAdd.setInt(2, Integer.parseInt(objRegisterVO.getCityId()));
int addId=pstmtGetAdd.executeUpdate();
if(addId>0)
{
ResultSet rsVal=pstmtGetAdd.getGeneratedKeys();
rsVal.next();
addId=rsVal.getInt(1);
}
If you are using Spring JDBC, you can use Spring's GeneratedKeyHolder class to get the inserted ID.
See this answer...
How to get inserted id using Spring Jdbctemplate.update(String sql, obj...args)
If you are using JDBC (tested with MySQL) and you just want the last inserted ID, there is an easy way to get it. The method I'm using is the following:
public static Integer insert(ConnectionImpl connection, String insertQuery){
Integer lastInsertId = -1;
try{
final PreparedStatement ps = connection.prepareStatement(insertQuery);
ps.executeUpdate(insertQuery);
final com.mysql.jdbc.PreparedStatement psFinal = (com.mysql.jdbc.PreparedStatement) ps;
lastInsertId = (int) psFinal.getLastInsertID();
connection.close();
} catch(SQLException ex){
System.err.println("Error: "+ex);
}
return lastInsertId;
}
Also, (and just in case) the method to get the ConnectionImpl is the following:
public static ConnectionImpl getConnectionImpl(){
ConnectionImpl conexion = null;
final String dbName = "database_name";
final String dbPort = "3306";
final String dbIPAddress = "127.0.0.1";
final String connectionPath = "jdbc:mysql://"+dbIPAddress+":"+dbPort+"/"+dbName+"?autoReconnect=true&useSSL=false";
final String dbUser = "database_user";
final String dbPassword = "database_password";
try{
conexion = (ConnectionImpl) DriverManager.getConnection(connectionPath, dbUser, dbPassword);
}catch(SQLException e){
System.err.println(e);
}
return conexion;
}
Remember to add the connector/J to the project referenced libraries.
In my case, the connector/J version is the 5.1.42. Maybe you will have to apply some changes to the connectionPath if you want to use a more modern version of the connector/J such as with the version 8.0.28.
In the file, remember to import the following resources:
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.SQLException;
import com.mysql.jdbc.ConnectionImpl;
Hope this will be helpful.
Connection cn = DriverManager.getConnection("Host","user","pass");
Statement st = cn.createStatement("Ur Requet Sql");
int ret = st.execute();
my method in my class(MissionDAO) package dao;
public static void planf() throws SQLException {
Connection con = null;
PreparedStatement ps = null;
try {
con = Database.getConnexion();
ps = con.prepareStatement("UPDATE vehicule SET disponible='FALSE' WHERE matricule=455555");
// set the preparedstatement parameters
ps.setString(1,disponible);
ps.executeUpdate();
ps.executeQuery();
System.out.println("no change ");
} catch (Exception ex) {
ex.getStackTrace();
System.out.println("no update ");
} finally {
Database.close(con);
}
}
And i can insert in database without problemes
In your code you have a few issues:
In your PreparedStatement you have no placeholders '?' for parameter values. The statement ps.setString(1,disponible); will therefore do nothing.
disponible is undefined here so is probably a class member, but you do not show us how that value is set in code or retrieved in the planf method.
You have the statement ps.executeUpdate(); for the update, which is fine and all you need. The statement ps.executeQuery(); is wrong because ps is not returning a ResultSet.
I am looking for different ways of performing bulk insert into database (e.g. SQL Server 2012) from a Java application. I need to insert lot of entities into database very efficiently without making as many calls to database as there are entities.
My requirement is to perform a bulk insert of entities, where an insert of entity in database could involve inserting data into one or more tables. The following are the two ways which I can think of:
Dynamically generate a batch of SQL statements and execute it against the database by making use of native JDBC support.
Construct XML representation of all the entities and then invoke a stored procedure by passing the generated XML. The stored procedure takes care of parsing the XML and inserting the entities to database.
I am new to Java and not having enough knowledge of available frameworks. IMO, the above two approaches seems to be very naive and not leveraging the available frameworks. I am requesting experts to share different ways of achieving bulk insert along with its pros and cons. I am open to MyBatis, Spring-MyBatis, Spring-JDBC, JDBC, etc which solves the problem in an efficient manner.
Thanks.
I have a demo ,JDBC batch processing
file:demo.txt
The content
1899942 ,demo1
1899944 ,demo2
1899946 ,demo3
1899948 ,demo4
Insert the data reads the file content
my code:
public class Test2 {
public static void main(String[] args) {
long start = System.currentTimeMillis();
String sql = "insert into mobile_place(number,place) values(?,?)";
int count=0;
PreparedStatement pstmt = null;
Connection conn = JDBCUtil.getConnection();
try {
pstmt = conn.prepareStatement(sql);
InputStreamReader is = new InputStreamReader(new FileInputStream(new File("D:/CC.txt")),"utf-8");
BufferedReader br = new BufferedReader(is);
conn.setAutoCommit(false);
String s1 = null;
String s2 = null;
while(br.readLine() != null){
count++;
String str = br.readLine().toString().trim();
s1 = str.substring(0, str.indexOf(","));
s2 = str.substring(str.indexOf(",")+1,str.length());
pstmt.setString(1, s1);
pstmt.setString(2, s2);
pstmt.addBatch();
if(count%1000==0){
pstmt.executeBatch();
conn.commit();
conn.close();
conn = JDBCUtil.getConnection();
conn.setAutoCommit(false);
pstmt = conn.prepareStatement(sql);
}
System.out.println("insert "+count+"line");
}
if(count%1000!=0){
pstmt.executeBatch();
conn.commit();
}
long end = System.currentTimeMillis();
System.out.println("Total time spent:"+(end-start));
} catch (Exception e) {
e.printStackTrace();
}finally{
try {
pstmt.close();
conn.close();
} catch (SQLException e) {
e.printStackTrace();
}
}
}
}
//getConnection()//get jdbc Connection
public static Connection getConnection(){
try {
Class.forName("com.mysql.jdbc.Driver");
} catch (ClassNotFoundException e) {
e.printStackTrace();
}
try {
conn = DriverManager.getConnection(url, userName, password);
} catch (SQLException e) {
e.printStackTrace();
}
return conn;
}
Speak for the first time, I hope I can help
I am the demo above use PreparedStatement [Read data calls a PreparedStatement one-off inserted]
JDBC batch There are 3 ways
1.use PreparedStatement
demo:
try {
Class.forName("com.mysql.jdbc.Driver");
conn = DriverManager.getConnection(o_url, userName, password);
conn.setAutoCommit(false);
String sql = "INSERT adlogs(ip,website,yyyymmdd,hour,object_id) VALUES(?,?,?,?,?)";
PreparedStatement prest = conn.prepareStatement(sql,ResultSet.TYPE_SCROLL_SENSITIVE,ResultSet.CONCUR_READ_ONLY);
for(int x = 0; x < size; x++){
prest.setString(1, "192.168.1.1");
prest.setString(2, "localhost");
prest.setString(3, "20081009");
prest.setInt(4, 8);
prest.setString(5, "11111111");
prest.addBatch();
}
prest.executeBatch();
conn.commit();
conn.close();
} catch (SQLException ex) {
Logger.getLogger(MyLogger.class.getName()).log(Level.SEVERE, null, ex);
}
2.use Statement.addBatch methods
demo:
conn.setAutoCommit(false);
Statement stmt = conn.createStatement(ResultSet.TYPE_SCROLL_SENSITIVE, ResultSet.CONCUR_READ_ONLY);
for(int x = 0; x < size; x++){
stmt.addBatch("INSERT INTO adlogs(ip,website,yyyymmdd,hour,object_id) VALUES('192.168.1.3', 'localhost','20081009',8,'23123')");
}
stmt.executeBatch();
conn.commit();
3.Direct use of the Statement
demo:
conn.setAutoCommit(false);
Statement stmt = conn.createStatement(ResultSet.TYPE_SCROLL_SENSITIVE,
ResultSet.CONCUR_READ_ONLY);
for(int x = 0; x < size; x++){
stmt.execute("INSERT INTO adlogs(ip,website,yyyymmdd,hour,object_id) VALUES('192.168.1.3', 'localhost','20081009',8,'23123')");
}
conn.commit();
Using the above method Insert the 100000 pieces of data Time consuming：
method 1:17.844s
method 2:18.421s
method 3:16.359s
MS JDBC versions later than 4.1 have SQLServerBulkCopy class that I assume is equivalent to one available in .Net and theoretically it should work as fast as bcp command line utility.
https://msdn.microsoft.com/en-us/library/mt221490%28v=sql.110%29.aspx
you can custom your code with JDBC，there is no framework support your requirement
I have been trying with the following code.
The connection is being made. But the resultSet is coming as empty (not null), whereas there are a couple of entries (2 fields each) in the database for the same.
It does not enter the while condition. I'm new to JDBC, please help!
My code is:
import java.sql.*;
public class JDBCTest123
{
public static void main(String[] args)
{
System.out.println("oracle Connect Example.");
Connection conn = null;
String url = "jdbc:oracle:thin:#127.0.0.1:1521:XE";
String driver = "oracle.jdbc.driver.OracleDriver";
String userName = "system";
String password = "mumpymamai";
Statement stmt = null;
String query = "select * from table1";
try
{
Class.forName(driver);
conn = DriverManager.getConnection(url, userName, password);
stmt = conn.createStatement();
System.out.println("Connected to the database");
ResultSet rs = stmt.executeQuery(query);
while (rs.next())
{
System.out.println(rs.getString(1));
System.out.println(rs.getString(2));
}
conn.close();
System.out.println("Disconnected from database");
} catch (Exception e)
{
e.printStackTrace();
}
}
}
And the output is:
oracle Connect Example.
Connected to the database
Disconnected from database
So few suggestions. I recommend to you use PreparedStatements which are more faster and safer.
PreparedStatement ps = null;
conn = DriverManager.getConnection(url, userName, password);
ps = conn.prepareStatement(query);
ResultSet rs = ps.executeQuery();
while (rs.next())
{
// do some work
}
Second suggestion, call close() method in finally block, because application may crash and then your connection won't be closed. Finally block guarantees that will be always called.
Third suggestion if it doesn't work without Exception, probably you have empty table.