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Java Database Connection Class keeps returning Connection as Null

I have created a Public Class for my Database connection as am running various Database query's throughout the application
Every time i call the Class con always returns Null
But if i use it outside of the Class, and directly in the Activity then it connects and runs.
I have no idea why and would greatly appreciate any pointers in the right direction please.
Here are my ConnectionManager class:
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;
public class ConnectionManager {
static String serverName ="192.168.1.5";
static String serverPort ="1433";
static String databaseName ="DBNAME";
static String db = String.format("jdbc:jtds:sqlserver://%s:%s/%s", serverName, serverPort, databaseName);
static String un = "sa";
static String pass = "";
static Connection con;
public static Connection getConnection() {
try {
try {
Class.forName("net.sourceforge.jtds.jdbc.Driver");
con = DriverManager.getConnection(db, un, pass);
} catch (SQLException ex) {
// log an exception. fro example:
System.out.println("Failed to create the database connection.");
}
} catch (ClassNotFoundException ex) {
// log an exception. for example:
System.out.println("Driver not found.");
}
return con;
}
}
And from within my Activity i am calling it as follow:
try {
con = ConnectionManager.getConnection();
if (con == null) {
z = "Check Your Internet Access!";
Toast.makeText(StockEnquiry.this, z, Toast.LENGTH_LONG).show();
} else {
stmt = con.createStatement();
String query = "select * from Details where ID= '1111' ";
rs = stmt.executeQuery(query);
if (rs.next()) {
String sCode = rs.getString("Short_Code");
String sDesc = rs.getString("Short_Desc");
Toast.makeText(StockEnquiry.this, (sCode + " " + sDesc), Toast.LENGTH_LONG).show();
con.close();
} else {
Toast.makeText(StockEnquiry.this,"Invalid Code!", Toast.LENGTH_LONG).show();
}
Toast.makeText(StockEnquiry.this, "Message1", Toast.LENGTH_LONG).show();
}
} catch (Exception ex) {
isSuccess = false;
z = ex.getMessage();
Toast.makeText(StockEnquiry.this, "Appears to have failed in catch", Toast.LENGTH_LONG).show();
}
}
}

So the message i was getting back was: android.os.NetworkOnMainThreadException'
After some digging i believe i am facing the issue because i am not running it as a asynchronous task.
Its possible to remove this restriction
StrictMode.ThreadPolicy policy = new StrictMode.ThreadPolicy.Builder().permitAll().build();
StrictMode.setThreadPolicy(policy);
So the connection class would look like the following.
import android.os.StrictMode;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;
public class ConnectionManager {
static StrictMode.ThreadPolicy policy = new StrictMode.ThreadPolicy.Builder().permitAll().build();
static String serverName ="192.168.1.1";
static String serverPort ="1433";
static String databaseName ="DatabaseName";
static String db = String.format("jdbc:jtds:sqlserver://%s:%s/%s", serverName, serverPort, databaseName);
static String un = "Username";
static String pass = "Password";
static Connection con;
public static Connection getConnection() {
try {
try {
StrictMode.setThreadPolicy(policy);
Class.forName("net.sourceforge.jtds.jdbc.Driver");
con = DriverManager.getConnection(db, un, pass);
} catch (SQLException ex) {
// log an exception. fro example:
System.out.println("Failed to create the database connection.");
}
} catch (ClassNotFoundException ex) {
// log an exception. for example:
System.out.println("Driver not found.");
}
return con;
}
}
Calling the code from within the activity is untouched from the original post.
As a knock-on effect from this, You may get Application Crash / Lock-ups or slowness on poor network connection / coverage.
So its a bit of a sacrifice, but can be handled in other ways.

How to get a String from a field

I've got a mysql question within java. I've got a mysql database with different tables. I currently got a database called 'litebans' and a table called 'litebans_mutes'.
Within that table there is a row called reason and under that reason (let's say what's within reason) there's a string called 'This is a test' and 'sorry'; how would I get the string 'This is a test' and 'sorry' associated with the same 'uuid' row in java? Here is a picture explaining more:
Here is an image explaining the sql format
Additionally, i've currently initialized all variables and such in java, i currently have this code:
http://hastebin.com/odumaqazok.java (Main class; using it for a minecraft plugin)
The below code is the MySQL class; api used to connect and execute stuff.
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import net.octopusmc.punish.Core;
public class MySQL {
public static Connection openConnection() {
try {
Class.forName("com.mysql.jdbc.Driver");
} catch (ClassNotFoundException e1) {
System.err.println(e1);
e1.printStackTrace();
}
try {
Connection conn = DriverManager.getConnection("jdbc:mysql://" + Core.host + ":" + Core.port + "/" + Core.database, Core.user, Core.pass);
System.out.println("Currently connected to the database.");
return conn;
} catch (SQLException e) {
System.out.println("An error has occured while connecting to the database");
System.err.println(e);
e.printStackTrace();
}
return null;
}
public static void Update(String qry) {
try {
Statement stmt = Core.SQLConn.createStatement();
stmt.executeUpdate(qry);
stmt.close();
} catch (Exception ex) {
openConnection();
System.err.println(ex);
}
}
public static Connection getConnection() {
return Core.SQLConn;
}
public static ResultSet Query(String qry) {
ResultSet rs = null;
try {
Statement stmt = Core.SQLConn.createStatement();
rs = stmt.executeQuery(qry);
} catch (Exception ex) {
openConnection();
System.err.println(ex);
}
return rs;
}
}
An example using that api above is shown below:
try {
ResultSet rs = MySQL.Query("QUERY GOES HERE");
while (rs.next()) {
//do stuff
}
} catch (Exception err) {
System.err.println(err);
err.printStackTrace();
}
tl;dr: I want to get the two fields called 'reason' with the give 'uuid' string field.

First , make sure that your using the jdbc mysql driver to connect to the database
Defile a class where you could write the required connection and create statement code.
For example
class ConnectorAndSQLStatement {
ResultSet rs = null;
public Statement st = null;
public Connection conn = null;
public connect() {
try {
final String driver = "com.mysql.jdbc.Driver";
final String db_url = "jdbc:mysql://localhost:3306/your_db_name";
Class.forName(driver);//Loading jdbc Driver
conn = DriverManager.getConnection(db_url, "username", "password");
st = conn.createStatement();
rs = st.executeQuery("Select what_you_want from your_table_name");
while (rs.next()) {
String whatever = rs.getInt("whatever ");
System.out.print(whatever);
}
} catch (SQLException se) {
se.printStackTrace();
} catch (Exception e) {
e.printStackTrace();
}
Just call this function and the magic :D
Hope it is helpful

Connection from CachedRowSet

I have the following Java 7 code to create a CachedRowSet.
CachedRowSet crs = RowSetProvider.newFactory().createCachedRowSet();
Is there a way to get the Connection object from the CachedRowSet object? I would like to set autoCommit to false on the Connection object before invoking the acceptChanges() on CachedRowSet as I'm getting the following exception when invoking acceptChanges().
javax.sql.rowset.spi.SyncProviderException: Can't call commit when autocommit=true
There is a COMMIT_ON_ACCEPT_CHANGES field on CachedRowSet, but it's Deprecated.

Well, it took some time for me to reproduce the issue at my end. Setting the autoCommit value of the Connection to false via conn.setAutoCommit(false); resolved this issue.
Following is the sample working program:
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;
import javax.sql.rowset.CachedRowSet;
import javax.sql.rowset.RowSetProvider;
public class CRSetChecker {
public static void main(String[] args) {
String connectString = "jdbc:oracle:thin:scott/tiger" +
"#(DESCRIPTION=(ADDRESS=(PROTOCOL=tcp)" +
"(HOST=myorahost)(PORT=5521))" +
"(CONNECT_DATA=(SID=myorasid)))";
//Get DB connection
Connection conn = (new CRSet()).getConnection(connectString);
if (conn == null) {
System.out.println("Connection failed");
System.exit(0);
} else {
System.out.println("Connection established successfully!");
try {
CachedRowSet crs =
RowSetProvider.newFactory().createCachedRowSet();
String query="select ename from emp";
crs.setCommand(query);
crs.execute(conn);
//Set auto commit false
conn.setAutoCommit(false);
int count = 0;
while(crs.next()){
String name = crs.getString(1);
count++;
System.out.println(name);
if(count==1){
crs.updateString(1, "COOPER");
crs.updateRow();
crs.acceptChanges(conn);
System.out.println("After update:"+crs.getString(1));
}
}
conn.close();
} catch (SQLException e1) {
e1.printStackTrace();
}
}
}
public Connection getConnection(String connectString)
{
Connection con = null;
try {
try {
Class.forName("oracle.jdbc.OracleDriver");
} catch (ClassNotFoundException e) {
e.printStackTrace();
}
con = DriverManager.getConnection(connectString);
} catch (SQLException ex) {
ex.printStackTrace();
}
return con;
}
}

MySQL JDBC returning 0 results

It seems a very basic question but I couldn't find any resolution for it.
I have following code with me:
package com.test.db.util;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
public class JDBCConnect
{
private Connection conn = null;
private final String uname = "root";
private final String passwd = "test#123";
private String url = "jdbc:mysql://127.0.0.1:3306/TrainDB";
private final String className = "com.mysql.jdbc.Driver";
public void initConnection()
{
try
{
if(this.conn == null || this.conn.isClosed())
{
try
{
Class.forName (className).newInstance ();
this.conn = DriverManager.getConnection(url, uname, passwd);
System.out.println("database connection established.");
}
catch(SQLException sqe)
{
sqe.printStackTrace();
}
catch (InstantiationException e)
{
e.printStackTrace();
}
catch (IllegalAccessException e)
{
e.printStackTrace();
}
catch (ClassNotFoundException e)
{
e.printStackTrace();
}
}
}
catch(SQLException sqle)
{
sqle.printStackTrace();
}
//return this.conn;
}
public void disconnect()
{
if (conn != null)
{
try
{
conn.close ();
System.out.println ("Database connection terminated");
}
catch (Exception e) { /* ignore close errors */ }
}
}
public void insertData(String sql)
{
PreparedStatement s;
try
{
if(conn == null || conn.isClosed())
{
initConnection();
}
s = conn.prepareStatement(sql);
int count = s.executeUpdate ();
s.close ();
System.out.println (count + " rows were inserted");
}
catch (SQLException e)
{
e.printStackTrace();
if (conn != null)
{
try
{
conn.close ();
System.out.println ("Database connection terminated");
}
catch (Exception se) { /* ignore close errors */ }
}
}
}
public ResultSet query(String sql)
{
Statement s = null;
try
{
if(this.conn == null || this.conn.isClosed())
{
initConnection();
}
s = conn.createStatement();
s.executeQuery(sql);
ResultSet rs = s.getResultSet();
System.out.println("lets see " + rs.getFetchSize());
return rs;
}
catch(SQLException sq)
{
System.out.println("Error in query");
return null;
}
finally
{
try {
s.close();
} catch (SQLException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
}
I am using JDBCConnect in a different class:
import java.sql.ResultSet;
import java.sql.SQLException;
public class traininfo
{
public static void main(String[] args)
{
JDBCConnect jdbcConn = new JDBCConnect();
String sql = "SELECT id FROM testtable";
ResultSet rs = jdbcConn.query(sql);
try {
System.out.println(rs.getFetchSize());
} catch (SQLException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
if(rs != null)
{
try
{
while(rs.next())
{
System.out.println(rs.getString("id"));
}
rs.close();
}
catch(SQLException sqe)
{
}
}
jdbcConn.disconnect();
}
}
I am not using concurrent calls for insertion and reads. If I use the same query in mysql-workbench (client), I am getting proper results but using the mentioned code, I am getting
database connection established.
lets see 0
0
Database connection terminated
Please suggest me what I am missing?

Most probably it's because you're closing Statement before you are using it's ResultSet. It's strange that it doesn't throw an exception, but this is not correct anyway.
As per Statement.close method JavaDoc:
When a Statement object is closed, its current ResultSet object, if one exists, is also closed.
I suggest to use some kind of callback to retrieve results from ResultSet before it's closed e.g.:
public <T> T query(String sql, IResultSetHandler<T> resultSetHandler ) throws SQLException {
Statement statement = null;
try {
statement = connection.createStatement();
final ResultSet rs = connection.executeQuery(sql);
final T result = resultSetHandler.handle(rs);
return result;
} finally {
if(statement != null) {
statement.close();
}
}
}
public interface IResultSetHandler<T> {
T handle(ResultSet rs);
}
public static void main(String[] args) {
JDBCConnect jdbcConn = new JDBCConnect();
List<String> ids = jdbcConn.query(sql, new IResultSetHandler<List<String>>() {
public List<String> handle(ResultSet rs) {
List<String> ids = new ArrayList<String>();
while(rs.next()) {
ids.add(rs.getString("id"));
}
return ids;
}
});
}
Or to use commons apache dbutils library which does exactly the same.

ResultSet.getFetchSize() lets you know the maximum number of rows that the connection will fetch at once. You can set it with ResultSet.setFetchSize(int). See also the official documentation. It does not tell you how many rows in total you will get. If the fetch size is left to zero, JDBC decides on its own.
Other than that, refer to Yura's answer which addresses the core of your problem.

Could it be because you never call InsertRows, as it never shows that 'X rows were inserted'

Returning the Connection from JDBC into a main method of Java?

Is it possible to return the type Connection?
And use it as a method passed by reference through out the program?
I find it makes the database interaction a lot easier if it is passed as a method.
public static Connection database(String database, String username, String password) {
String url = "jdbc:postgresql:" + database;
//LOAD DRIVER
try {
Class.forName("org.postgresql.Driver");
}
catch (ClassNotFoundException e) {
e.printStackTrace();
}
//CONNECT TO DATABASE
try {
Connection conn = DriverManager.getConnection(url, username, password);
return conn;
} catch (SQLException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
return null;
}
public static void main(String[] args) {
db = database("java_jdbc", "admin", "fake_password_1234");
}

You can do that.
Just remember to invoke close() on the connection to release its resources when done.

package mySystem;
import java.sql.*;
import javax.swing.*;
public class MySqlConnector {
Connection conn = null;
public static Connection ConnectDB() {
try {
Class.forName("com.mysql.jdbc.Driver"); //register jdbc driver
Connection conn = DriverManager.getConnection("jdbc:mysql://localhost/inventory_db", "root", "");
// JOptionPane.showMessageDialog(null, "Connected to db");
return conn;
} catch (Exception e) {
JOptionPane.showMessageDialog(null, e);
return null;
}
}
}