We Keep Coding

Oracle JDBC UCP and Java

I'm wondering if anyone can shed some light on this topic, as I have been racking my brain for days and can't quite understand why this does not work. I have three classes
main, RetrieveDBVersion,GetOracleConnection I've been doing some testing with oracle JDBC, UCP and Java 1.7.
According to the Oracle documentation, If I use connection pooling the connection will be returned to the pool as soon as I close the connection, Invalidate it and set it to null See Here. So I decided to give it a whirl and see if it would perform just like the documentation says it should. In my Main application I have a simple loop which makes a connection 200 times by calling RetrieveDBVersion. RetrieveDBVersion is simply performing a query and returning the driver version. My loop works fine until I hit the magic number of 68 and then I receive an error which states
java.sql.SQLException: Exception occurred while getting connection:
oracle.ucp.UniversalConnectionPoolException:
Cannot get Connection from Datasource: java.sql.SQLException:
Listener refused the connection with the following error:
ORA-12516, TNS:listener could not find available handler with matching protocol stack
These are the detail of the 3 methods. These methods are not in a server environment. They are simply calling a local oracle express database and I'm running them from my desktop. Why would I keep getting this error? If I'm returning the connections back to the pool?
Main
import com.jam.DB.JDBCVersion;
import static java.lang.System.out;
public class MainApp {
public static void main(String[] args) {
String myMainJDBCVar;
try{
for(int i=1; i<200; i++ )
{
myMainJDBCVar= JDBCVersion.RetrieveDBVersion();
out.println(myMainJDBCVar + " " + i);
}
out.println("this is Done!");
}
catch (Exception e) {
System.out.println(e.getMessage());
}
}
}
RetrieveDBVersion
import java.sql.*;
import oracle.ucp.jdbc.ValidConnection;
public class JDBCVersion {
public static String DBVersion;
public static String RetrieveDBVersion()throws SQLException {
Connection conn = JDBCConnection.GetOracleConnection("test");
try {
DatabaseMetaData meta = conn.getMetaData();
//get driver info
System.out.println("JDBC driver version is " + meta.getDriverMajorVersion());
DBVersion = meta.getDriverVersion();
} catch (SQLException e) {
e.printStackTrace();
DBVersion = e.getMessage();
}
finally {
System.out.println("hit the finally clause");
((ValidConnection) conn).setInvalid();
conn.close();
conn=null;
}
return DBVersion;
}
GetOracleConnection
import oracle.ucp.jdbc.PoolDataSource;
import oracle.ucp.jdbc.PoolDataSourceFactory;
import java.sql.*;
public class JDBCConnection {
public static Connection GetOracleConnection(String Enviroment) throws SQLException{
PoolDataSource pds = PoolDataSourceFactory.getPoolDataSource();
Connection conn = null; //ora.defaultConnection();
try {
pds.setConnectionFactoryClassName("oracle.jdbc.pool.OracleDataSource");
pds.setURL("jdbc:oracle:thin:#//localhost:1521/xe");
pds.setUser("system");
//pds.setInitialPoolSize(5);
pds.setPassword("xxx");
pds.setMaxStatements(10);
conn = pds.getConnection();
return conn;
}
catch(Exception e){
e.printStackTrace();
}
return conn;
}

So after careful though and getting a little extra help from the Oracle forum. I finally understand why the above referenced code is giving the error message that I'm receiving. See Here For Response
Because I'm setting the data source everytime the loop goes around, I'm essentially creating more than one pool. The way to do this, is create one pool and than pull connections from that pool.
New code to replace the GetOracleConnection I created a singleton class for datasource and in code I simply retrieve the connection from the data source like such
Connection conn = Database.getInstance().GetPoolSource().getConnection();
package com.jam.DB;
import oracle.ucp.jdbc.PoolDataSource;
import oracle.ucp.jdbc.PoolDataSourceFactory;
public class Database {
private static Database dbIsntance;
private static PoolDataSource pds;
private Database() {
// private constructor //
}
public static Database getInstance() {
if (dbIsntance == null) {
dbIsntance = new Database();
}
return dbIsntance;
}
public PoolDataSource GetPoolSource() {
if (pds == null) {
pds = PoolDataSourceFactory.getPoolDataSource();
try {
pds.setConnectionFactoryClassName("oracle.jdbc.pool.OracleDataSource");
pds.setURL("jdbc:oracle:thin:#//localhost:1521/xe");
pds.setUser("system");
pds.setPassword("xxxx");
pds.setMaxStatements(15);
return pds;
} catch (Exception e) {
}
return pds;
}
return pds;
}
}

MySQL insert query not working in aws rds abruptly

I have a java based web application in which am inserting a row in aws MySQL database.
The problem is that, after 1-2 hours, the code stops inserting the rows in the database and am not getting any sort of error in my log files.
The structure of the table is as below:
Now when am calling the servlet, am using this piece of code.
JSONObject result=t_s.ro(jc.getT_conn(), t,true);
t is the json and true/false ia a boolean value according to my case.
Now inside jc.getT_conn() am using this code:
public static Connection getT_conn() throws ClassNotFoundException, JSONException {
Connection c=null;
if(t_conn==null)
{
c=rds_conn();
}
else
{
c=t_conn;
}
return c;
}
Here t_conn is a global variable for that java file and rds_conn() returns me a new connection after creating it.
Now from t_s.ro class am calling a function which inserts the row into the database based on a condition, if that's satisfied.
Here is the code:
public static boolean dPOI(Connection conn,String d,String u,ArrayList<String> l,ArrayList<String> li) throws SQLException
{
long startTime=System.currentTimeMillis();
System.out.println("Time for sql start is : "+System.currentTimeMillis());
PreparedStatement stmt = null;
boolean action=false;
try {
String sql="INSERT INTO `ce`.`cse`(`twsD`,`twsID`,`twsi`)VALUES(?,?,?)";
stmt = conn.prepareStatement(sql);
stmt.setString(1, u);
stmt.setString(2, d);
stmt.setString(3, l.toString()+"~"+li.toString());
System.out.println(stmt.toString());
action = stmt.execute();
//conn.close();
} catch (SQLException e) {
// handle sql exception
System.out.println("SQL Exception");
e.printStackTrace();
}catch (Exception e) {
// TODO: handle exception for class.forName
System.out.println("Exception");
e.printStackTrace();
}
stmt.close();
long endTime=System.currentTimeMillis();
System.out.println("Time taken inside sql Query is : "+(endTime-startTime));
return action;
}
Below is the log file which am getting.
Time for sql start is : 1486393105661
com.mysql.jdbc.JDBC42PreparedStatement#59037dda: INSERT INTO `ce`.`cse`(`twsD`,`twsID`,`twsi`)VALUES('Bana','2fdb0c926765','[\'FOM\', \'MONEY CENTER KOLA - BAORE\']~[83.80, 272.20]')
Time taken inside sql Query is : 1
Now if you can see, I am not getting any SQL exception or any other kind of exception. And moreover, the time taken is always 1 (when it stops inserting) otherwise it's somewhere between 20-25.
Moreover, thee auto increment ID always gets used up, by that what I mean is if the last row was inserted at ID 1, the subsequent query which I insert through MySQL workbench has an ID somewhere around 40 i.e if we assume that 39 of the remaining rows didn't get inserted.

Taking Mark B's comment as a starting point, I decided to create a connection pool which will be providing the connections.
Below is the code which I used:
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import org.apache.commons.dbcp2.BasicDataSource;
public final class Database {
private static final String SQL_EXIST = "show tables;";
public static void main(String[] args) throws SQLException {
// TODO Auto-generated method stub
boolean exist = false;
try (
Connection connection = Database.getConnection();
PreparedStatement statement = connection.prepareStatement(SQL_EXIST);
)
{
try (ResultSet resultSet = statement.executeQuery()) {
exist = resultSet.next();
}
}
System.out.println("Value is : "+ exist);
}
private static final BasicDataSource dataSource = new BasicDataSource();
static {
dataSource.setDriverClassName("com.mysql.jdbc.Driver");
dataSource.setUrl("CONNECTION_STRING");
dataSource.setUsername("USERNAME");
dataSource.setPassword("PASSWORD");
dataSource.setMaxTotal(100);
}
private Database() {
//
}
public static Connection getConnection() throws SQLException {
return dataSource.getConnection();
}
}
FIrst function was just for testing purpose.
Now after creating this Database class, just call Database.getConnection() whenever you need to get the connection. The connection pool will take care of providing you with a valid connection.
Correct me if am wrong.

Sqlite cannot insert data when database insider src folder

I spend like 5 hour re-writing all methods cause thought i make mistake while inserting data into DB BUT i noticed everything is fine when i got database outside src folder.
This is my code
public class DataBaseModel {
public static final String DRIVER = "org.sqlite.JDBC";
// public static final String DB_URL = "jdbc:sqlite::resource:sqlite/databse.db"; // insider src/sqlite
public static final String DB_URL = "jdbc:sqlite:database.db";
private Connection conn=null;
private Statement stat=null;
public DataBaseModel() {
try {
Class.forName(DataBaseModel.DRIVER);
} catch (ClassNotFoundException e) {
System.err.println("NO JDBC DRIVER");
e.printStackTrace();
}
try {
conn = DriverManager.getConnection(DB_URL);
stat = conn.createStatement();
} catch (SQLException e) {
System.err.println("Connection problem");
e.printStackTrace();
}
createTables();
}
When i got my project setup like that:
public static final String DB_URL = "jdbc:sqlite:database.db";
everythin work fine:
creating records
display records form db
creating tables
But when i change to
public static final String DB_URL = "jdbc:sqlite::resource:sqlite/databse.db";
there is an error
Connection problem java.sql.SQLException: resource sqlite/database.db not found: java.net.MalformedURLException: no protocol: sqlite/database.db
I get rid of error unconsciously by copping database to src/sqlite thats why i was unable to see any error for all that time ...
Any idea what cause problem when database.db is inside src/sqlite?
I explained as much as i can.
Thx for help

cannot load JDBC Driver

I'm trying to understand JDBC API and in order to do so,I'm just writing some code to estabilish a connection to the DB. It seems that I can't...
I'm trying to manually load the Driver for mysql DB,but even if I include the connector .jar in the classpath the compiler complains that it can't find the package com.mysql.
If,on the other hand,I omit the Class.forName() method, the code compiles but I get a hundreds Exception lines at runtime.
I'm compiling (and running) including the jar in the command line:
javac -cp [path to jar] DBTest.java
here's my code:
import java.sql.*;
class DBTest {
**strong text**
static final String ADDRESS="jdbc:mysql://127.0.0.1:8888/customer";
static final String USER="myuser";
static final String PASSWORD="luca";
public static void main(String[] args) {
Connection conn=null;
Statement stat=null;
Class.forName("com.mysql.jdbc.Driver");
try {
conn=DriverManager.getConnection(ADDRESS,USER,PASSWORD);
stat=conn.createStatement();
String query="SELECT * FROM person";
ResultSet result=stat.executeQuery(query);
while (result.next()) {
String name=result.getString("name");
String surname=result.getString("surname");
int id=result.getInt("id");
String telephone=result.getString("telephone");
System.out.println(id+": first name: "+name+" second name: "+surname+" tel: "+telephone);
}
}
catch (SQLException e) {
e.printStackTrace();
}
finally {
try {
conn.close();
stat.close();
}
catch (Exception e) {
e.printStackTrace();
}
}
}
Edit:
with the double quotes it now compiles fine, but at runtime it says something like:
com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: Communications link failure

Replace
Class.forName(com.mysql.jdbc.Driver);
with
Class.forName("com.mysql.jdbc.Driver");

Java newbie needs help in database connection

I'm new to Java and even newer to java database connections. I've managed to create a database connection and query a table when I put it in the Main class. Now that I've moved it into a new class called Connection I am getting errors:
package lokate;
import java.sql.DriverManager;
import java.sql.SQLException;
import java.sql.Statement;
import java.sql.ResultSet;
public class Connection {
private static Statement stmt = null;
private static ResultSet rs = null;
private static Connection con = null;
public Connection() throws SQLException {
try {
Class.forName("com.mysql.jdbc.Driver");
String connectionUrl = "jdbc:mysql://localhost:3306/Lokate?" +
"user=root&password=";
con = DriverManager.getConnection(connectionUrl);
stmt = con.createStatement();
retriveData("SELECT * FROM Users");
int rowsEffected = 0;
} catch (SQLException sqlEx) {
System.out.println("SQL Exception: "+ sqlEx.toString());
} catch (ClassNotFoundException classEx) {
System.out.println("Class Not Found Exception: "+ classEx.toString());
} catch (Exception Ex) {
System.out.println("Exception: "+ Ex.toString());
}
}
public static void retriveData(String SQL) throws Exception {
rs = stmt.executeQuery(SQL);
while (rs.next())
{
System.out.println(rs.getString("fname") + " : " + rs.getString("lname"));
}
}
}
I'm getting an error saying cannot find symbol. Symbol:method createStatement() and incomparable types for con = DriveManager.....
Can anyone help?
Also, is it best practice to put the connection in the class like this then call a new object every time I want to do something with the db?
Regards,
Billy

I'd say your code is an example of many worst practices. Let me count the ways:
Your Connection class is a poor abstraction that offers nothing over and above that of java.sql.Connection.
If you use your class, you'll never get to take advantage of connection pooling.
You hard wire your driver class, your connection URL, etc. You can't change it without editing and recompiling. A better solution would be to externalize such things.
Printing an error message in the catch blocks is far less information than supplying the entire stack trace.
Your code hurts my eyes. It doesn't follow the Sun Java coding standards.
Your retrieveData method is utterly worthless. What will you do with all those printed statements? Wouldn't it be better to load them into a data structure or object so the rest of your code might use that information?
It's rowsAffected - "affect" is the verb, "effect" is the noun. Another variable that's not doing any good.
You're on the wrong track. Rethink it.
I think you'll find this code more helpful.
package persistence;
import java.sql.*;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
public class DatabaseUtils
{
public static Connection createConnection(String driver, String url, String username, String password) throws ClassNotFoundException, SQLException
{
Class.forName(driver);
if ((username == null) || (password == null) || (username.trim().length() == 0) || (password.trim().length() == 0))
{
return DriverManager.getConnection(url);
}
else
{
return DriverManager.getConnection(url, username, password);
}
}
public static void close(Connection connection)
{
try
{
if (connection != null)
{
connection.close();
}
}
catch (SQLException e)
{
e.printStackTrace();
}
}
public static void close(Statement st)
{
try
{
if (st != null)
{
st.close();
}
}
catch (SQLException e)
{
e.printStackTrace();
}
}
public static void close(ResultSet rs)
{
try
{
if (rs != null)
{
rs.close();
}
}
catch (SQLException e)
{
e.printStackTrace();
}
}
public static void rollback(Connection connection)
{
try
{
if (connection != null)
{
connection.rollback();
}
}
catch (SQLException e)
{
e.printStackTrace();
}
}
public static List<Map<String, Object>> map(ResultSet rs) throws SQLException
{
List<Map<String, Object>> results = new ArrayList<Map<String, Object>>();
try
{
if (rs != null)
{
ResultSetMetaData meta = rs.getMetaData();
int numColumns = meta.getColumnCount();
while (rs.next())
{
Map<String, Object> row = new HashMap<String, Object>();
for (int i = 1; i <= numColumns; ++i)
{
String name = meta.getColumnName(i);
Object value = rs.getObject(i);
row.put(name, value);
}
results.add(row);
}
}
}
finally
{
close(rs);
}
return results;
}
}

Your problem is that DriverManager.getConnection returns a java.sql.Connection. Since your class is also called Connection you are getting a name clash between lokate.Connection and java.sql.Connection. You Will need to specify the fully qualified class name where ever you want to use java.sql.Connection, otherwise lokate.Connection is assumed.
Specify fully qualified class name like so:
java.sql.Connection con = null;
// ....
con = DriverManager.getConnection(connectionUrl);
Alternatively, rename your Connection class to something else and you will not get this naming conflict.

Connection is an existing type in the java.sql package, which is what DriverManager.getConnection returns. You have named your class as Connection too, so this is causing the confusion. The simplest way out would be to rename your class to something else and add an import java.sql.Connection; at the top.

Also, is it best practice to put the connection in the class like this then call a new object every time I want to do something with the db?
I think the best practice would be to use an existing solution to this problem, so that you can avoid re-inventing the wheel and focus on what makes your problem unique.
If you are writing a server application (it isn't clear whether you are), then I would also consider using a database connection pool. Creating new database connections on the fly is not efficient and doesn't scale well. You can read about database connection issues in this article I wrote a while back.