Im trying to gain access to my database using a project in order to input information like username and password so that if the input is correct, then i can access details about that certain account, but before all that, there's an error that says "java.lang.ClassNotFoundException:org.apache.derby.jdbc.EmbeddedDriver"
and im not sure how to fix it, i checked other solutions saying to check my URL, which i have done and fixed but it still is an error
public static void main(String[] args) {
Connection con = null;
Statement stmt = null;
try{
//REGISTER THE DRIVERS
Class.forName(JDBC_Driver1);
Class.forName(JDBC_Driver2);
//ESTABLISH CONNECTION TO DB
System.out.println("Connecting to a selected Database....");
con=DriverManager.getConnection(URL,USER,PASS);
System.out.println("CONNECTED SUCCESSFULLY");
}
catch (Exception e){
System.err.println(e);
I am not sure which IDE you are using. I will explain this in terms of the Netbeans IDE.
Firstly, you will need to make sure you have a Glassfish type server. They can be found in the "services" tab.
Secondly, you need to make sure your derby database is connected. In netbeans if it is not connected, it will have a broken looking icon next to it. If this is the case, right click and hit connect.
One of the benefits to a derby database is that it has a built in set of drivers, so it is unnecessary to provide a driver class.
If you are completely starting out fresh and have not changed your username or password, the following code has all of the default information to connect to the sample database that is created when you download glassfish server.
public class DataAccessDerby {
private static final String URL = "jdbc:derby://localhost:1527/sample";
private static final String USER = "app";
private static final String PASS = "app";
Connection con;
Statement stmt;
public void openConnection() throws ClassNotFoundException, SQLException {
con = DriverManager.getConnection(URL, USER, PASS);
}
public void closeConnection() throws SQLException {
if (con != null) {
con.close();
}
}
public static void main(String[] args) {
DataAccessDerby derby = new DataAccessDerby();
try {
System.out.println("Connecting to a selected Database....");
derby.openConnection();
System.out.println("CONNECTED SUCCESSFULLY");
derby.closeConnection();
} catch (ClassNotFoundException | SQLException e) {
System.err.println(e);
}
}
}
I hope this helps.
Related
I'm currently working on a college project, and I'm creating a very simple e-commerce style website.
I'm using JDBC driver manager and connection pool for the connection to the db, while using Tomcat 9.0 as the container.
The problem is: when I modify some product through the website (let's say the amount available for example), the website doesn't always reflect the changes, while I can always see the data correctly in MySql Workbench.
It actually works one time out of two on the same query:
I run the query for the first time after the changes -> it shows the old value
I run the query for the second time after the changes -> it shows the new value
I run the query for the third time after the changes -> it shows the old value
And so on.
I've already tried to set caching off (from the query, using the SQL_NO_CACHE), but it didn't seem to solve the problem, I've tried to use Datasource instead, but it causes other problems that most likely I won't have the time to solve.
This is the connection pool file, which I think might be problem, I'm not that sure tho:
public class DriverManagerConnectionPool {
private static List<Connection> freeDbConnections;
static {
freeDbConnections = new LinkedList<Connection>();
try {
Class.forName("com.mysql.cj.jdbc.Driver");
} catch (ClassNotFoundException e) {
System.out.println("DB driver not found:"+ e.getMessage());
}
}
private static synchronized Connection createDBConnection() throws SQLException {
Connection newConnection = null;
String ip = "localhost";
String port = "3306";
String db = "storage";
String username = "root";
String password = "1234";
newConnection = DriverManager.getConnection("jdbc:mysql://"+ ip+":"+ port+"/"+db+"?useUnicode=true&useJDBCCompliantTimezoneShift=true&useLegacyDatetimeCode=false&serverTimezone=UTC", username, password);
newConnection.setAutoCommit(false);
return newConnection;
}
public static synchronized Connection getConnection() throws SQLException {
Connection connection;
if (!freeDbConnections.isEmpty()) {
connection = (Connection) freeDbConnections.get(0);
freeDbConnections.remove(0);
try {
if (connection.isClosed())
connection = getConnection();
} catch (SQLException e) {
connection.close();
connection = getConnection();
}
} else {
connection = createDBConnection();
}
return connection;
}
public static synchronized void releaseConnection(Connection connection) throws SQLException {
if(connection != null) freeDbConnections.add(connection);
}
}
I really hope you can help me, I haven't found any solution online!
I guess it is because of auto-commit is disabled. Please try using #Transactional or set auto-commit to true. You can also try to use db.commit after each statement.
As per your connection pool implementation, all connection in your pool seems to be auto committed false.
Please check you have properly committed the connection after executing the query or not.
So it might be the case that, when executing the query after changes with same connection it reflects those changes, done earlier and on other connections, old values are might get returned.
I'm creating a JavaFX application, I've connected to the database fine. However when i look to get data from the tables i get the error
org.h2.jdbc.JdbcSQLException: Table "LECTURE" not found; SQL
statement: SELECT NAME FROM Lecture [42102-192]
and I'm 100% sure i'm connected to the database and the table is definitely there, any suggestions on why this is?
hear is my connection code and the code i am running just so you can see
public class ConnectionFactory {
//static reference to itself
private static ConnectionFactory instance = new ConnectionFactory();
public static final String URL = "jdbc:h2:file:~/db\\.";
public static final String USER = "notepad";
public static final String PASSWORD = "password";
public static final String DRIVER_CLASS = "org.h2.Driver";
//private constructor
private ConnectionFactory() {
try {
Class.forName(DRIVER_CLASS);
} catch (ClassNotFoundException e) {
e.printStackTrace();
}
}
private Connection createConnection() {
Connection connection = null;
try {
connection = DriverManager.getConnection(URL, USER, PASSWORD);
} catch (SQLException e) {
System.out.println("ERROR: Unable to Connect to Database.");
}
return connection;
}
public static Connection getConnection() {
return instance.createConnection();
}
}
And the query being run
private void onLoadYearSelect() {
try {
Connection con = ConnectionFactory.getConnection();
Statement stat = con.createStatement();
String query = "SELECT NAME FROM Lecture";
ResultSet years = stat.executeQuery(query);
while(years.next()){
yearSelect.setValue(years.getString("NAME"));
System.out.println(years.getString("NAME"));
}
} catch (SQLException e) {
e.printStackTrace();
}
}
public void initialize(){
onLoadYearSelect();
}
If it says the table doesn't exist, then it really doesn't exist.
Most likely, you are not actually connecting to the correct database. In fact, by default, if the connection string points to a non-existent database, it just creates an empty database on the fly, which would explain your error.
It's probably too late now (because there is probably a 2nd database created already somewhere), but to avoid this confusion, it's not a bad idea to include IFEXISTS=TRUE in the connection string so that it fails if the database doesn't exist, rather than creating an empty one that will mask the true problem.
public static final String URL = "jdbc:h2:file:~/db\\.;IFEXISTS=TRUE";
However, one thing you can still try to debug the problem, is to add IFEXISTS=TRUE to the connection string. Then move or rename the database you think it should be connecting to so as to make the connection string invalid. Basically, force it to fail. If the code still connects to the database successfully, then you'll know the connection string is not pointing to the location you think it is.
import java.sql.*;
class ConnectSql
{
static Connection cont(String db)throws Exception
{
Class.forName("com.mysql.jdbc.Driver");
Connection con=DriverManager.getConnection("jdbc:mysql://localhost:3306/"+db+","root","xyz" );
return(con);
}
}
I am facing a problem in compiling this function and this 7th line is i suppose a problem is there an syntax error.If so please tell me.Here i want to take the name of database as parameter received from calling function.When i gave the exact name of database instead of parameter it worked,but not after i passed parameter in connection line.
it should be
Connection con=DriverManager.getConnection("jdbc:mysql://localhost:3306/"+db,"root","xyz" );
problem is
"+db+"
you have extra " mark
Connection con=null;
String DB_URL = "jdbc:mysql://localhost:3306/";
String USER = "abc";//db user name
String PASS = "abc";//db password
public synchronized Connection getConnection(String dbname)
{
try
{
Class.forName("com.mysql.jdbc.Driver");//loading mysql driver
con = DriverManager.getConnection(DB_URL+dbname,USER,PASS);//connecting to mysql
}
catch(Exception e)
{
e.printStackTrace();
}
return con;
}
i have a java application which connects to mysql database using MYSQL connector. problem is when application started, MYSQL process list shows many connections than i requested in process list (attached image).
i have two threads running which connects to database within 5 seconds and 11 seconds. but, when i refresh mysql process list, it shows server's host ports are changing rapidely than threads are running. normally its changing 3-5 ports per second. can someone please guide me any optimizing issues or any changes to test with this?
thanks
P.S.
I have created a class which connects to DB at initialization and that class's object is in a places where needs DB connectivity. and that class having all methods which using to query from DB.
EDIT
my database connectivity class code is
public class Data{
static Connection con; //create connection
static Statement stmt; //create statement
static ResultSet rs; //create result set
static HostRead hr = new HostRead();
static int db_port = 3306;
static String db_root = "127.0.0.1";
static String db_name = "chsneranew";
static String db_user = "root";
static String db_pass = "";
/**Constructer method*/
public Data(){
this(db_root,db_port,db_name,db_user,db_pass);
if(getConnection()==null){
System.out.println("error in database connection");
}
else{
con = getConnection();
}
}
protected void finalize() throws Throwable {
try {
System.out.println("desctroyed");
con.close();
} finally {
super.finalize();
}
}
public static Connection getConnection(){
try{
Class.forName("com.mysql.jdbc.Driver").newInstance();
Connection conn = DriverManager.getConnection("jdbc:mysql://"+db_root+":"+db_port+"/"+db_name, db_user, db_pass);
stmt = conn.createStatement();
return conn;
}
catch(ClassNotFoundException er){
JOptionPane.showMessageDialog(null,"Error found ...\nDataBase Driver error (Invalid Drivers)\nUsers Cant login to system without database\n\nContact System Administrator","Error",JOptionPane.ERROR_MESSAGE);
return null;
}
catch(Exception er){
JOptionPane.showMessageDialog(null,"Error found ...\nDataBase Access error (Invalid Authentication)\nOr\nDataBase not found. Details are not be loaded \n\nUsers Cant login to system without database\n\nContact System Administrator","Error",JOptionPane.ERROR_MESSAGE);
return null;
}
}
public String getUserName(){
try{
Statement stmt2 = getConnection().createStatement();
ResultSet rss2;
String sql = "SELECT name FROM gen";
rss2 = stmt2.executeQuery(sql);
if(rss2.next()){
return rss2.getString("name");
}
}
catch(Exception er){
er.printStackTrace();
}
return null;
}
}
i am calling getUserName()method in my threads. using
Data d = new Data();
d.getUserName();
conn.close();
You need to close the connection, the connection is not closed that is why it is still there in the list. You need to Connection conn above so that it may be visible to rest of the code.
You are calling the getConnection() method three times when you want to read the data via the getUserName() method. Two times in the constructor when your constructor of the Data class is called (one for the if(...) check, one for the con = getConnection() line) and one time when you actually want to read the data at the getConnection().createStatement() line. So you have three connections to the database, and that is just the getUserName method...
Rewrite your code that only one connection is established and this connection is reused for any further execution.
I have started trying out some stuff so that I can use mysql database together with Java. First of all I have some questions about it.
I have used mysql a lot with PHP development but never with Java. Can I use the MySQL that MAMP brings or do I have to install it stand alone or something?
and second.. I have created this code with the help of a tutorial but the only output I get is
com.mysql.jdbc.Driver
The code that I have used for this you can find below:
package Databases;
import java.sql.*;
public class MysqlConnect{
/* These variable values are used to setup
the Connection object */
static final String URL = "jdbc:mysql://localhost:3306/test";
static final String USER = "root";
static final String PASSWORD = "root";
static final String DRIVER = "com.mysql.jdbc.Driver";
public Connection getConnection() throws SQLException {
Connection con = null;
try {
Class.forName(DRIVER);
con = DriverManager.getConnection(URL, USER, PASSWORD);
}
catch(ClassNotFoundException e) {
System.out.println(e.getMessage());
System.exit(-1);
}
return con;
}
public void getEmployees() {
ResultSet rs = null;
try {
Statement s = getConnection().createStatement();
rs = s.executeQuery("SELECT id, name, job_id, location FROM person");
System.out.format("%3s %-15s %-7s %-7s%n",
"ID", "NAME", "JOB ID",
"LOCATION");
System.out.format("%3s %15s %7s %7s%n",
"---", "---------------",
"-------", "--------");
while(rs.next()) {
long id = rs.getLong("id");
String name = rs.getString("name");
long job = rs.getLong("job_id");
String location = rs.getString("location");
System.out.format("%-3d %-15s %7d %5s%n",
id, name, job, location);
}
}
catch(SQLException e) {
System.out.println(e.getMessage());
System.exit(-1);
}
}
}
It's coming from the following block:
catch(ClassNotFoundException e) {
System.out.println(e.getMessage());
System.exit(-1);
}
That's a pretty poor way of handling exceptions. You're just printing the exception message. You have no clue what's going on. Rather just throw it (which will end up with a nice stacktrace), or print a more descriptive message along alone the exception message, e.g.
catch(ClassNotFoundException e) {
System.out.println("JDBC driver class not found in runtime classpath: " + e.getMessage());
System.exit(-1);
}
How to fix the particular exception is in turn actually a second question (with a pretty obvious answer: just put JAR file containing JDBC driver class in runtime classpath), but ala, you may find this mini-tutorial helpful then: Connect Java to a MySQL database.
Unrelated to the concrete problem, I'm not sure which tutorial you're reading there, but I'd take it with a grain of salt. Apart from poor exception handling, it's also leaking DB resources in getEmployees() method by never closing the result set, statement and connection. This is absolutely not a good practice either. How to do it is also already covered in the aforelinked mini-tutorial. See further also: How often should Connection, Statement and ResultSet be closed in JDBC?
Yes, you need to install MySQL server locally or remotely.
The code will be usable if you also downloaded jdbc Driver jar from MySQL download pages. and you configured your MySQL instance with the proper username and password.