Develop Reference

Java SQL memory leak

I'm facing an issue where I have a java application running on a server, and it starts growing in memory until eventually the server cannot handle it anymore.
This is some sort of memory leak / resource leak problem, which I thought was extremely rare in Java due to the garbage collection. I guess something is being referenced and never used, so the garbage collector does not collect it.
The problem is that the size in memory grows so slowly that I'm not able to debug it properly (it may take two weeks to make the server unusable).
I'm using java + mysql-connector, and I'm sure the memory leak is caused by something related to the database connection.
Here is how I connect to the database:
private static Connection connect(){
try {
Connection conn = null;
conn = DriverManager.getConnection("jdbc:mysql://localhost:3306/database","client","password");
return conn;
}catch(SQLException ex){
System.out.println("SQLException: " + ex.getMessage());
System.out.println("SQLState: " + ex.getSQLState());
System.out.println("VendorError: " + ex.getErrorCode());
return null;
}
}
public static Connection getConnection(){
try {
if (connection == null || connection.isClosed()) connection = connect();
return connection;
}catch (SQLException exception){
System.out.println("exception trying to connect to the database");
return null;
}
}
I can't find any possible problem here, but who knows!
Here's how I retrieve information from the database:
public void addPoints(long userId,int cantidad){
try {
if(DatabaseConnector.getConnection()!=null) {
PreparedStatement stm = DatabaseConnector.getConnection().prepareStatement("UPDATE users SET points = points + ? WHERE id = ? ");
stm.setLong(2, userId);
stm.setInt(1, cantidad);
if(stm.executeUpdate()==0){ //user doesn't have any point records in the database yet
PreparedStatement stm2 = DatabaseConnector.getConnection().prepareStatement("INSERT INTO users (id,points) VALUES (?,?)");
stm2.setLong(1, userId);
stm2.setInt(2, cantidad);
stm2.executeUpdate();
}
}
}catch (SQLException exception){
System.out.println("error recording points");
}
}
public ArrayList<CustomCommand> getCommands(long chatId) throws SQLException{
ArrayList<CustomCommand> commands = new ArrayList<>();
if(DatabaseConnector.getConnection() != null) {
PreparedStatement stm = DatabaseConnector.getConnection().prepareStatement("SELECT text,fileID,commandText,type,probability FROM customcommands WHERE chatid = ?");
stm.setLong(1, chatId);
ResultSet results = stm.executeQuery();
if(!results.isBeforeFirst()) return null;
while (results.next()){
commands.add(new CustomCommand(results.getString(1),results.getString(2),results.getString(3), CustomCommand.Type.valueOf(results.getString(4)),results.getInt(5)));
}
return commands;
}
return null;
}
Maybe the problem is something related to exception catching and statements not being correctly executed? Maybe something related to result sets?
It's driving me crazy. Thanks for helping me!

You do nothing to clean up ResultSet and Statement before you return. That's a bad idea. You should be closing each one in individual try/catch blocks in a finally block.
A ResultSet is an object that represents a database cursor on the database. You should close it so you don't run out of cursors.
I wouldn't have a single static Connection. I'd expect a thread-safe, managed pool of connections.
I wouldn't return a null. You don't make clear what the user is supposed to do with that. Better to throw an exception.

"[SQLITE_ERROR] SQL error or missing database (near "DATABASE": syntax error)"

I am trying to create a new database file named test in the folder D:\sqlite, using JDBC, as follows:
import java.sql.*;
public class Class1 {
private static void createNewDataBase(){
String url = "jdbc:sqlite:D:sqlite/";
Connection conn = null;
Statement statement = null;
try{
conn = DriverManager.getConnection(url);
System.out.println("Connection Established");
statement = conn.createStatement();
} catch (SQLException e) {
System.out.println(e.getMessage());
}
try {
statement.execute("CREATE DATABASE test");
} catch (SQLException e) {
System.out.println(e.getMessage());
} finally{
try{
if(statement != null)
statement.close();
}catch(SQLException e){
System.out.println(e.getMessage());
}
try{
if(conn != null)
conn.close();
}catch(SQLException e){
System.out.println(e.getMessage());
}
}
}
public static void main(String[] args){
createNewDataBase();
}
}
When I run the project, I get the following output:
Connection Established
[SQLITE_ERROR] SQL error or missing database (near "DATABASE": syntax error)
Process finished with exit code 0
It says the syntax is wrong but I can't find the error. I've looked for answers for similar questions, but none solved my problem. Can anyone tell me what's the problem? Thanks in advance!

As already stated by #Andreas, there is no CREATE DATABASE SQL statement for SQLite. To create a new SQLite database you need to merely make a connection to one and it is automatically created (you do however need to ensure that the D:/sqlite/ path already exists within the local file system).
The following code should create an empty (no tables) SQLite Database named MyNewDatabase.sqlite within the folder sqlite located in the root of drive D of your local file system:
String dbPath = "D:/sqlite/MyNewDatabase.sqlite";
Connection conn = null;
try {
Class.forName("org.sqlite.JDBC");
conn = DriverManager.getConnection("jdbc:sqlite:" + dbPath;);
}
catch (ClassNotFoundException ex) {
ex.printStackTrace();
}
catch (SQLException ex) {
ex.printStackTrace();
}
finally {
try {
if (conn != null) {
conn.close();
}
}
catch (SQLException e) { e.printStackTrace(); }
}
Now you need to create one or more Tables for your new database to make it useful. SQLite does accept the CREATE TABLE SQL statement and you could do this through the same connection if desired.

The database exists, it has been connected i.e the database is the connection, which is basically the file. Hence there is no SQL for CREATE DATABASE.
Inside the database you would typically create tables (and perhaps other components).
e.g. CREATE TABLE mytable (mycolumn TEXT, myothercolumn INTEGER) which would create a table named mytable with 2 columns mycolumn and myothercolumn (the former being defined with a column type of TEXT, the latter with a column type of INTEGER).
As such, if you were to change :-
statement.execute("CREATE DATABASE test");
to :-
statement.execute("CREATE TABLE mytable (mycolumn TEXT, myothercolumn INTEGER)");
Note you'd only want to do this once, otherwise it would fail as the table already exists, so you could use CREATE TABLE IF NOT EXISTS mytable (mycolumn TEXT, myothercolumn INTEGER), of cousre it depends upon your requirements.
You may find that it will work. Obviously you will need to do other things such as add some data as the table will be empty.
Perhaps then try
statement.execute("INSERT INTO mytable VALUES('fred',100)");
Every time this is run a new ROW will be added to the table name mytable.

AS400 system connection with JNDI

I can figure out how to connect to an AS400 through jt400 with JNDI resources just fine:
Connection conn = null;
Statement stmt = null;
try {
Context ctx = (Context) new InitialContext().lookup("java:comp/env");
conn = ((DataSource) ctx.lookup("jdbc/AS400")).getConnection();
System.out.println(conn.getClientInfo());
stmt = conn.createStatement();
//SQL data fetch using the connection
ResultSet rs = stmt.executeQuery("SELECT * FROM LIBRARY.TABLE");
while (rs.next()) {
System.out.println(rs.getString("COLUMN1"));
}
conn.close();
conn = null;
}
catch(Exception e){System.out.println(e);}
However, another part of the application utilizes DataQueues (from the same jt400 library):
String queue = "/QSYS.LIB/" + libraryName +".LIB/" + queueName +".DTAQ";
try{
system = new AS400(server, user, pass);
DataQueue dq = new DataQueue(system, queue);
// Convert the Data Strings to IBM format
byte[] byteData = message.getBytes("IBM285");
dq.write(byteData);
System.out.println("Wrote to DataQueue");
}catch(Exception e){
e.printStackTrace();
System.err.println(e);
}finally{
// Make sure to disconnect
if(system != null){
try{
system.disconnectAllServices();
System.out.println("Disconnected from DataQueue.");
}catch(Exception e){
System.err.println(e);
}
}
}
Inside of this working code for DataQueues references server, user, pass, which isn't ideal.
I'd like to utilize the AS400 JNDI connection I already set up, but every example I see about connecting Java to DataQueues references an example much like this one.
The documentation all seem to point to AS400 system objects which are hard-coded references to servername, user, pass, etc.
Is there better way to utilize DataQueue() with a JNDI reference?

As assumed in the comments above, the DataQueue is not part of the JDBC connection at all, it can't be used to configure the connection for usage to reading and writing to a DataQueue. Since this is the case, it can't also share connection methods that JDBC uses even though the jt400 library connects with JDBC. A properties file or other server-based solutions is required unless a hard-coded connection is specified in the DataQueue/Java examples online (All 1 of them).

Unable to connect to Azure using JDBC (based upon the connection string and samples provide) due to SSL issue

Am getting the following error: com.microsoft.sqlserver.jdbc.SQLServerException: The driver could not establish a secure connection to SQL Server by using Secure Sockets Layer (SSL) encryption. Error: "Connection reset by peer: socket write error."
import java.sql.*;
import com.microsoft.sqlserver.jdbc.*;
public class SQLDatabaseConnection {
// Connect to your database.
// Replace server name, username, and password with your credentials
public static void main(String[] args) {
String connectionString =
"jdbc:sqlserver://XXXXX.database.windows.net:1433;"
+ "database=VDB;"
+ "user=XXX#VVV;"
+ "password=XXXX;"
+ "encrypt=true;"
+ "trustServerCertificate=false;"
+ "hostNameInCertificate=*.database.windows.net;"
+ "loginTimeout=30;";
// Declare the JDBC objects.
Connection connection = null;
Statement statement = null;
ResultSet resultSet = null;
try {
// Class.forName("com.microsoft.sqlserver.jdbc.SQLServerDriver");
connection = DriverManager.getConnection(connectionString);
// Create and execute a SELECT SQL statement.
String selectSql = "SELECT TOP 2 * from Application";
statement = connection.createStatement();
resultSet = statement.executeQuery(selectSql);
// Print results from select statement
while (resultSet.next()) {
System.out.println(resultSet.getString(2) + " "
+ resultSet.getString(3));
}
} catch (Exception e) {
e.printStackTrace();
} finally {
// Close the connections after the data has been handled.
if (resultSet != null) try {
resultSet.close();
} catch (Exception e) {
}
if (statement != null) try {
statement.close();
} catch (Exception e) {
}
if (connection != null) try {
connection.close();
} catch (Exception e) {
}
}
}
}
I'm only trying to do the "sample" connection snippet of code as referenced on the Azure site (which points to a MS entry), modified only to match my db and test table but without success.
Having reviewed all there is to know, I have:-
ensured that I'm using the right sqljdbc (I've tried all 4)
have the sqlauth.dll on the CLASSPATH
have set the sample up EXACTLY as shown; and incorporated the string that Azure offers.
I have tried various combinations of encrypt and trust without success. As I'm a newbie to Java and Azure, I'm reluctant and unsure how to fiddle with the JVM security settings.
I've proven that my machine can talk to the Azure database (through a VB ODBC connection); and I've tested with the firewall down.
Any thoughts?

I tried to reproduce the issue, but failed that I could access my SQL Azure Instance using the code which be similar with yours.
The difference between our codes is only as below, besides using the connection string of my sql azure instance.
Using the driver sqljdbc4.jar from the sqljdbc_4.0 link.
Using the code Class.forName("com.microsoft.sqlserver.jdbc.SQLServerDriver"); to load MS SQL JDBC driver.
Not adding the sqlauth.dll file into the CLASSPATH.
Check my client IP which has been allowed by SQL Azure IP firewall.
Using the sql select 1+1 to test my code, and get the value 4 from code result.getInt(1).
That's fine for me. If you can supply more detals for us, I think it's very helpful for analysising the issue.
Hope it helps.

What is causing the "near ".": syntax error" in my SQLite query?

I am trying to output my table as a .csv file. I am using the sqlite-jdbc java library to execute my query. Here are the statements:
.mode csv
.output test.csv
select * from geninfo;
.output stdout
and this is my java code:
try {
try {
// create a database connection
Class.forName("org.sqlite.JDBC");
} catch (ClassNotFoundException ex) {
Logger.getLogger(SQLite.class.getName()).log(Level.SEVERE, null, ex);
}
connection = DriverManager.getConnection("jdbc:sqlite:702Data.db");
Statement statement = connection.createStatement();
statement.setQueryTimeout(30); // set timeout to 30 sec.
statement.executeUpdate("create table if not exists geninfo (id TEXT, DeviceID TEXT)");
statement.executeUpdate(".mode csv");
statement.executeUpdate(".output test.csv");
statement.executeUpdate("select * from geninfo;");
statement.executeUpdate(".output stdout");
ResultSet rs = statement.executeQuery("select * from geninfo");
while (rs.next()) {
// read the result set
System.out.println("DeviceID = " + rs.getString("DeviceID"));
System.out.println("id = " + rs.getInt("id"));
}
} catch (SQLException e) {
// if the error message is "out of memory",
// it probably means no database file is found
System.err.println(e.getMessage());
} finally {
try {
if (connection != null) {
connection.close();
}
} catch (SQLException e) {
// connection close failed.
System.err.println(e);
}
}
}
I have tried adding parenthesis around the period and also removing the period and both cause the same syntax error.

Those commands are SQLite console commands, not pure SQL. JDBC can only handle SQL.
If you want to do this from java, try executing the shell command to open the console using ProcessBuilder and feed it the commands via its InputStream.
However, if calling from java is not necessary, you may be better served writing a shell script of some sort and using that directly, or calling the script from java.
If all you are using SQLite for is to parse the CSV file, consider not using SQLite at all and instead load the data directly from the file into your code using one of the several open source CSV parsing libraries out there. This approach will be order of magnitude faster and simpler.