I trying to make a connection to my DDBB in order to print all the columns from a table but I keep getting Null.
I have checked the connection parameters and everything seems correct.
I'm thinking that maybe there is something wrong with my query statement:
public List<Palabra> getTodos() throws SQLException {
SQLConexion con = new SQLConexion();
listaPalabras = new ListaPalabras();
if(con.ConectarBasedeDatos()) {
try{
Statement stmt = con.getConnection().createStatement();
ResultSet rs=stmt.executeQuery("SELECT * FROM PALABRA");
while(rs.next()) {
Palabra pal = new Palabra(rs.getInt("idPalabra"), rs.getString("palabra"), rs.getInt("dificultad")); //These are the columns that I need to print.
listaPalabras.addPalabra(pal); //adding the results to the list
}
}
catch(Exception e)
{
System.out.println(e);
}
}
else {
return null;
}
con.DesconectarBasedeDatos();
return listaPalabras.getListaPalabras();
}
I managed to solve the problem by adding the MySQL Connector to the libraries so indeed there was no connection with the database because of this.
Novice error.
Thanks a lot for your time.
Recently I'm just learning some HTML, JSP and servlets for a university project, the thing is that I made a database into MySQL Workbench with id primary key, auto increment , then some fields like username, password, firstname, lastname, and so on.
The goal is to make a login page and register page, for some reason if I push data with MySQL Workbench into the database it will let me retrieve it with my login form and my select statment, but for some reason I'm doing the same thing with register but in this case with the query INSERT.
So, after research, I did preparestatment and changed the executeQuery to executeUpdate and everything, but my log says a nullPointerException somewhere, I know it may be a simple and silly error that I'm not seeing, but I'm new at this. This is what U have made so far to insert data into my database:
public static UserBean registarUsuario(UserBean bean){
//preparing some objects for connection
Statement stmt = null;
ResultSet rs = null;
try {
Class.forName("com.mysql.jdbc.Driver");
} catch (ClassNotFoundException ex) {
System.out.println("Error al cargar el driver");
System.out.println(ex.getMessage());
}
String firstname = bean.getFirstName();
String lastname = bean.getLastName();
String username = bean.getUsername();
String password = bean.getPassword();
boolean admin = bean.isAdmin();
int tipo = bean.getType();
String insertQuery =
"insert into idusuario (firstname,lastname,username,password,admin,tipo) values ('"+firstname+"','"+lastname+"','"+username+"','"+password+"','"+admin+"','"+tipo+"')";
System.out.println("Firstname is " + firstname);
System.out.println("Surname is " + lastname);
System.out.println("Query: "+insertQuery);
try
{
//connect to DB
currentCon = DriverManager.getConnection("jdbc:mysql://localhost:3306/usuarios", "root", "admin");
rs = stmt.executeQuery(insertQuery);
...
My output:
Info: Query: insert into idusuario
(firstname,lastname,username,password,admin,tipo) values
('jhon','marston','jmar','123','true','0') Info: Error :
java.lang.NullPointerException
The thing is that Netbeans doesn't even tell me where the NPE is happening so I'm kind of confused, I don't know if the query is wrong or if something else is, because as I can see in my output, the query seems ok.
I leave you here my database structure
You are assigining the stmt as null and never initializing it.
Statement stmt = null;
ResultSet rs = null;
Then you are trying to use it:
rs = stmt.executeQuery(insertQuery);
You will need to do something like this before you use it:
PreparedStatement stmt=currentCon.prepareStatement(yourQuery);
So, after research, i did preparestatment and changed the executeQuery
to executeUpdate and everything, but my log says a
nullPointerException somewhere, i know it may be a simple and silly
error that im not seeing, but understand that im new at this. this is
what i have made so far to insert data into my database
When we use insert,update or delete we need to use executeUpdate.
When we use select we need to use executeQuery.
In your example you are doing executeQuery for an insert. This is wrong. You need to use this:
rs = stmt.executeUpdate(insertQuery);
You're getting a NPE because you are trying to retrieve the results where there are none.
Here is a nice thing to do to help you reduce boilerplate code... (so you don't have to keep repeating yourself with db initialization values)
Create a class for your database connection:
public class DBConnection {
private static String url = null;
private static Connection conn = null;
public static Connection getConnection(){
try{
Class.forName("com.mysql.jdbc.Driver");
url = "jdbc:mysql://localhost:3306/usuarios";
conn = DriverManager.getConnection(url,"root","admin");
} catch (Exception e) {
System.out.println(e);
}
return conn;
}
}
Now you can use this in all your other classes like this:
public static UserBean registarUsuario(UserBean bean){
try(Connection conn= DBConnection.getConnection()){
PreparedStatement pst = conn.prepareStatement("insert into idusuario (firstname,lastname,username,password,admin,tipo) values (?,?,?,?,?,?);");
pst.setString(1, bean.getFirstName());
pst.setString(2, bean.getLastName());
pst.setString(3, bean.getUserName());
pst.setString(4, bean.getPassword());
pst.setBoolean(5, bean.isAdmin());
pst.setInt(6, bean.getType());
pst.executeUpdate();
}catch (SQLException e) {
e.printStackTrace();
}
}
Code snippet:
On a button click, actionevent will be called
public void actionPerformed(ActionEvent e)
{
Function f = new Function();
Function is a nested class which i have used to establish the connection with the database.
The code snippet for function class is also provided in the end.
ResultSet rs = null;
String Cid ="cust_id";
String Pno="cust_phone";
String cat="cust_cat";
String start_date="st_date";
String Adv_amt="adv";
String Adv_end="end_date";
String Address="addr";
t2 is the Textfield name which i have used to get entry of customer name. I want to use this customer name as a PK to fetch all the other data about that customer from DB.
rs=f.find(t2.getText());
try{
if(rs.next())
{
t1.setText(rs.getString("cust_id"));
t3.setText(rs.getString("cust_phone"));
t4.setText(rs.getString("cust_cat"));
t5.setText(rs.getString("st_date"));
t6.setText(rs.getString("adv"));
t7.setText(rs.getString("end_date"));
t8.setText(rs.getString("addr"));
}
else
JOptionPane.showMessageDialog(null,"No data for this name");
}
catch(Exception ex)
{
JOptionPane.showMessageDialog(null,ex.getMessage());
}
}
Here is the code snippet for nested class Function which is inside the main class:
class Function{
Connection con=null;
ResultSet rs= null;
PreparedStatement ps = null;
public ResultSet find(String s)
{
try
{
DriverManager.registerDriver(new oracle.jdbc.driver.OracleDriver());
con = DriverManager.getConnection("jdbc:oracle:thin:#Localhost:1521:xe","system","qwerty");
ps= con.prepareStatement("Select * from gkkdb where cust_name='?'");
ps.setString(1,s);
rs= ps.executeQuery();
}
catch(Exception ex)
{
JOptionPane.showMessageDialog(null, ex.getMessage());
}
return rs;
}
}
Please help figure out the problem.
Don't put the parameter placeholder ? in single quotes.
This:
ps = con.prepareStatement("Select * from gkkdb where cust_name='?'");
should be
ps = con.prepareStatement("Select * from gkkdb where cust_name = ?");
The ? is not recognized as a placeholder if you enclose it in single quotes.
Sorting out the bind variable will fix your immediate issue.
You should explicitly specify what columns you want selected and that way you'll only get what you need (someone might add a BLOB column later) and you'll get them in the right order (someone might change the table create script before running on another DB instance, although you are looking up the columns by name, a different order would only impact if you were using positional indexes).
Ditto on the other answer re: bind variables (i.e. no quotes)
Plus, "select * from" is never a good idea, ask your DBA.
Obviously your code is for example, but you should make sure you free up any resources (Connection, Statement, ResultSet) as soon as they are done with. Use Java 7 try-with-resources.
I try to put some Data in my H2 database but I'm a total noob in databases so it throws error over error since more than a hour.
Normaly I can fix it somehow but now I got a new problem I try to use
getGeneratedKeys() first I tried to use AUTO_INCREMENT(1,1) but that didn't works too function but it won't work rigth.
The exception my programm throws is
org.h2.jdbc.JdbcSQLException: Funktion "GETGENERATEDKEYS" nicht gefunden
Function "GETGENERATEDKEYS" not found; SQL statement:
insert into logTbl values( getGeneratedKeys(),Webservice->startThread0: Thread0) [90022-173]
an my database function looks like this
public void createTable(String Log) {
try {
Class.forName("org.h2.Driver");
} catch (ClassNotFoundException e) {
System.err.println("TREIBER FEHLER");
e.printStackTrace();
}
Connection conn = null;
try {
conn = DriverManager.getConnection("jdbc:h2:~/DBtest/Logs");
Statement stat = conn.createStatement();
stat.execute("CREATE TABLE IF NOT EXISTS logTbl(ID INT PRIMARY KEY, LOG VARCHAR(255))");
//stat.execute("insert into test values(1, 'Hello')");
for (int i = 0; i < 20; i++) {
stat.execute("insert into logTbl values( getGeneratedKeys()," + Log + ")");
}
stat.close();
conn.close();
} catch (SQLException e) {
System.err.println("SQL FEHLER");
e.printStackTrace();
}
}
hope you can help me to fix my error as I said I'm totaly new and just had some code example as "tutorial" because I don't found a good tutorial
If you want to automatically generate primary key values, you need to first change the definition of your table:
CREATE TABLE IF NOT EXISTS logTbl
(
ID integer AUTO_INCREMENT PRIMARY KEY,
LOG VARCHAR(255)
);
You should also use a PreparedStatement rather than concatenating values.
So your Java code would look something like this:
String insert = "insert into logTbl (log) values(?)";
PreparedStatement pstmt = connection.prepareStatement(insert, Statement.RETURN_GENERATED_KEYS);
pstmt.executeUpdate();
ResultSet rs = pstmt.getGeneratedKeys();
long id = -1;
while (rs.next())
{
rs.getLong(1);
}
It might be that you need to use the overloaded version of prepareStatement() where you supply the column to be returned. Not sure which one works with H2:
prepareStatement(insert, new String[] {"ID"});
Btw: there is nothing "magic" about 255 as the length of a varchar column. There is no performance difference between varchar(500), varchar(20)or varchar(255). You should use the length that you expect you need, not some "magic" limit you think performs better.
Here is my stored procedure:
CREATE OR REPLACE PROCEDURE VIEWBROKERS
(o_username OUT USERS.USERNAME%TYPE)
AS
BEGIN
SELECT USERNAME
INTO o_username
FROM USERS
WHERE Role_ID = 3 ;
END VIEWBROKERS;
Here is my method calling the stored procedure:
public ResultSet pullBrokers() {
ResultSet rs = null;
try {
DriverManager.registerDriver(new oracle.jdbc.driver.OracleDriver());
con = DriverManager.getConnection(Messages.getString("OracleUserManagement.0"), Messages.getString("OracleUserManagement.1"), Messages.getString("OracleUserManagement.2")); //$NON-NLS-1$ //$NON-NLS-2$ //$NON-NLS-3$
String storedProcedure = "{call VIEWBROKERS(?)}";
CallableStatement statement = con.prepareCall(storedProcedure);
statement.registerOutParameter(1, java.sql.Types.VARCHAR);
rs = statement.executeQuery();
con.commit();
con.close();
} catch (SQLException e) {
e.printStackTrace();
}
return rs;
}
And lastly when I tried to print out the results:
public class TEST {
public static void main(String[] args) throws SQLException{
OraclePullListOfUsers pull = new OraclePullListOfUsers();
ResultSet rs = pull.pullBrokers();
try {
while (rs.next()){
System.out.println(rs.getString(1));
}
} catch (SQLException e) {
e.printStackTrace();
}
}
}
I get the error message ORA-01422: exact fetch returns more than requested number of rows
Which is strange ,because there are only two rows of data in the table...
If someone could point me in the right the direction, that would be awesome!
Looks like you're problem is not related to Java, just on the SQL side. Could it be that both those two rows in the table have Role_ID=3?
The root cause for your problem:
ORA-01422: exact fetch returns more than requested number of rows
is that PL/SQL select into statement expects a query to match to exactly one row. If the query returns no rows or if the query return more than one row (as in your case) it will throw an exception.
You can't use select into to save the results to a single out variable if the query can return more than one row. Instead your subprogram should return a cursor (that is a pointer to a record set) that your Java component can query. Note that returning a cursor is not the only option, but in your case it looks like a good starting point.
This issue has been addressed several times in StackExchange universe. Please take a look e.g.
Return many rows on a plsql Oracle10g
How to return multiple rows from the stored procedure? (Oracle PL/SQL)
Calling Oracle PL/SQL stored procedure from java middle tier using JDBC on Linux?
A Java example Using Ref Cursors To Return Recordsets.