I'm trying to connect to my DB using JDBC. I wanted to make a method for connection and another method for selecting data. I am getting a red line in Eclipse on the 'Connection con = connectDB();' part. ( See also attached) Cany anyone give me advice?
public class DBJdbc {
//Statement stmt = null;
// connecting to DB
public void connectDB() {
//Connection con = null;
try {
Class.forName("com.mysql.cj.jdbc.Driver");
Connection con = DriverManager.getConnection("jdbc:mysql://****/SAC?useSSL=false&serverTimezone=UTC", "***", "***");
}
catch(SQLException e) {
e.printStackTrace();
}
catch(ClassNotFoundException e) {
e.printStackTrace();
}
}
// a method for selecting DB
public static void select() {
//connectDB();
String sql = "SELECT * from SAC_SUR";
try(Connection con = connectDB(); // I'm getting a red line here)
PreparedStatement pstmt = con.prepareStatement(sql)){
Statement stmt = con.createStatement();
ResultSet rs = stmt.executeQuery(sql);
while(rs.next()) {
int id = rs.getInt(1);
String name = rs.getString(2);
System.out.println("Id = " + id + "name = " + name);
} //while
} catch(SQLException e) {
System.out.println(e.getMessage());
}
}
red line here!!!
connectDB() method is of void type and not returning anything but when you are calling the method, you are assigning it to variable con. So you need to change the return type of connectDb to the Connection type.
public Connection connectDB() {
Connection con = null;
try {
Class.forName("com.mysql.cj.jdbc.Driver");
con = DriverManager.getConnection("jdbc:mysql://****/SAC?useSSL=false&serverTimezone=UTC", "***", "***");
}
catch(SQLException e) {
e.printStackTrace();
}
catch(ClassNotFoundException e) {
e.printStackTrace();
}
return con;
}
You are trying to call non-static method into the static area, which is not allowed in Java. So I made this method static and returning the database connection.
Please update the below method into your code. It will resolve your problem.
public static Connection connectDB() {
Connection con = null;
try {
Class.forName("com.mysql.cj.jdbc.Driver");
con = DriverManager.getConnection("jdbc:mysql://****/SAC?useSSL=false&serverTimezone=UTC", "", "");
} catch(SQLException e) {
e.printStackTrace();
} catch(ClassNotFoundException e) {
e.printStackTrace();
}
return con;
}
Related
How to Close Statements and Connection in This Method
public static ResultSet getData (String query){
try {
Connection con = ConnectionProvider.connect();
Statement st = con.createStatement();
ResultSet rs = st.executeQuery(query);
return rs;
} catch (Exception e) {
JOptionPane.showMessageDialog(null, e);
System.out.println(e);
return null;
}
You need to close connections in finally block:
try {
...
}
catch {
...
}
finally {
try { st.close(); } catch (Exception e) { /* Ignored */ }
try { con.close(); } catch (Exception e) { /* Ignored */ }
}
In Java 7 and higher you can define all your connections and statements as a part of try block:
try(Connection con = ConnectionProvider.connect();
Statement st = con.createStatement();
ResultSet rs = st.executeQuery(query);
) {
// Statements
}
catch(....){}
One should use try-with-resources to automatically close all.
Then there is the p
public static void processData (String query, Consumer<ResultSet> processor){
try (Connection con = ConnectionProvider.connect();
Statement st = con.createStatement();
ResultSet rs = st.executeQuery(query)) {
processor.accept(rs);
} catch (SQLException e) {
JOptionPane.showMessageDialog(null, e);
System.getLogger(getClass().getName()).log(Level.Error, e);
}
}
processData("SELECT * FROM USERS", rs -> System.out.println(rs.getString("NAME")));
Or
public static <T> List<T> getData (String query, UnaryOperator<ResultSet, T> convert){
try (Connection con = ConnectionProvider.connect();
Statement st = con.createStatement();
ResultSet rs = st.executeQuery(query)) {
List<T> result = new ArrayList<>();
while (rs.next()) {
result.add(convert.apply(rs));
}
return result;
} catch (SQLException e) {
System.getLogger(getClass().getName()).log(Level.Error, e);
throw new IllegalArgumentException("Error in " + query, e);
}
}
Then there is the danger with this function, that users will compose query strings like:
String query = "SELECT * FROM USERS WHERE NAME = '" + name + "'";
Which does not escape the apostrophes like in d'Alembert. It opens the gates to SQL injection, a large security breach. One needs a PreparedStatement, and then can use type-safe parameters.
As with try-with-resources the code already is reduced (no explicit closes), you should drop this kind of function. But almost most programmers make this mistake.
App looks like this
In my Database class I have a method connect() and generateCSV(),
First one looks like this:
public void connect() throws Exception {
System.out.println("Begining of connect method");
try {
Class.forName("com.microsoft.sqlserver.jdbc.SQLServerDriver");
} catch (ClassNotFoundException e) {
throw new Exception("Driver not found");
}
String ser = "<ser name>";
String user = "<user name>";
String pass = "<password>";
String dbURL = "jdbc:sqlserver://" + ser + ";user=" + user + ";password=" + pass;
con = (Connection) DriverManager.getConnection(dbURL);
System.out.println("Connected! " + con);
}
and the second one generateCSV() like this
public void generate_CSV(String db,String tbl,String date, String out) {
try {
connect();
} catch (Exception e1) {
// TODO Auto-generated catch block
e1.printStackTrace();
}
ResultSet rs = null;
try {
CallableStatement st = con
.prepareCall("{call dbo.generate_CSV(?,?,?,?)}");
st.setEscapeProcessing(true);
st.setString(1, db);
st.setString(2, tbl);
st.setString(3, date);
st.setString(4, out);
rs= st.executeQuery();
} catch (SQLException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
When I fire event and call generateCSV method, method will call connect() and connect to the server and afterwards call my procedure written in mssql.
Unfortunately I receive this...
com.microsoft.sqlserver.jdbc.SQLServerException: Could not find stored
procedure 'dbo.generate_CSV'.
What am I missing?
I tried it without specifying the schema but nothing changes.
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
When i run my website it on glassfish server everything works fine but after some time its stop responding and I need to restart glassfish.. I think its cause I not closing the connection. Can someone tell me if this is the problem? if yes how to close it? Here is one of my function.
public Album get_album (String title)
{
try{
//creates a connection to the server
Connection cn = getCon().getConnection();
//prepare my sql string
String sql = "SELECT * FROM albums WHERE Title = ?";
//create prepared statement
PreparedStatement pst = cn.prepareStatement(sql);
//set sql parameters
pst.setString(1, title);
//call the statement and retrieve results
ResultSet rs = pst.executeQuery();
if(rs.next()) {
Album a = new Album();
a.setIdAlbum(rs.getInt("idAlbum"));
a.setTitle(rs.getString("Title"));
a.setYear(rs.getInt("Year"));
a.setIdArtist(rs.getInt("idArtist"));
a.setIdUser(rs.getInt("idUser"));
a.setLike(rs.getInt("Like"));
a.setDislike(rs.getInt("Dislike"));
a.setNeutral(rs.getInt("Neutral"));
a.setViews(rs.getInt("Views"));
return a;
}
}
catch (Exception e) {
String msg = e.getMessage();
}
return null;
}
Assumming the unique error in your application is for not closing the resources after using them, your code should change to:
public Album get_album (String title) {
Connection cn = null;
PreparedStatement pst = null;
ResultSet rs = null;
Album a = null;
try{
//creates a connection to the server
cn = getCon().getConnection();
//prepare my sql string
String sql = "SELECT * FROM albums WHERE Title = ?";
//create prepared statement
pst = cn.prepareStatement(sql);
//set sql parameters
pst.setString(1, title);
//call the statement and retrieve results
rs = pst.executeQuery();
if (rs.next()) {
a = new Album();
a.setIdAlbum(rs.getInt("idAlbum"));
a.setTitle(rs.getString("Title"));
a.setYear(rs.getInt("Year"));
a.setIdArtist(rs.getInt("idArtist"));
a.setIdUser(rs.getInt("idUser"));
a.setLike(rs.getInt("Like"));
a.setDislike(rs.getInt("Dislike"));
a.setNeutral(rs.getInt("Neutral"));
a.setViews(rs.getInt("Views"));
//don't return inside try/catch
//return a;
}
} catch (Exception e) {
String msg = e.getMessage();
//handle your exceptions
//e.g. show them in a logger at least
e.printStacktrace(); //this is not the best way
//this will do it if you have configured a logger for your app
//logger.error("Error when retrieving album.", e);
} finally {
closeResultSet(rs);
closeStatement(pst);
closeConnection(cn);
}
return a;
}
public void closeConnection(Connection con) {
if (con != null) {
try {
con.close();
} catch (SQLException e) {
//handle the exception...
}
}
}
public void closeStatement(Statement st) {
if (st!= null) {
try {
st.close();
} catch (SQLException e) {
//handle the exception...
}
}
}
public void closeResultSet(ResultSet rs) {
if (rs!= null) {
try {
rs.close();
} catch (SQLException e) {
//handle the exception...
}
}
}
Hello I have this class that contains a actionPerformed to perform a query it looks like this
MysqlConnect db = new MysqlConnect();
#Override
public void actionPerformed(ActionEvent e) {
if(e.getSource() == openKnop) {
try {
db.connectToAndQueryDatabase("test", "root", "root");
System.out.println("connection established");
Statement st = db.createStatement();
String query = "SELECT id, name, job_id, location FROM person WHERE name = 'Tom Swift'";
st.executeQuery(query);
System.out.println("Selected query succesfull");
} catch (SQLException e1) {
e1.printStackTrace();
}
finally {
db.closeCon();
System.out.println("connection closed");
}
}
and my MysqlConnect(); class looks like this
public class MysqlConnect{
protected Connection con;
public void connectToAndQueryDatabase(String database, String username, String password) throws SQLException {
con = null;
try {
con = DriverManager.getConnection(
"jdbc:mysql://localhost:3306/" + database,
username,
password);
} catch (SQLException e) {
e.printStackTrace();
}
}
public void closeCon() {
con = null;
}
}
but the problem is at the line
Statement st = db.createStatement();
it doesn't work like i've expected. I'm getting a undefined error.. how can I solve this?
The error says that db an reference of 'MysqlConnect ' doesn't have createStatement method. you need a Connection object. Make your connectToAndQueryDatabase to return Connection object
public Connection connectToAndQueryDatabase(String database, String username, String password) throws SQLException {
//your code
return con;
}
and :
Connection conn = db.connectToAndQueryDatabase("test", "root", "root");
System.out.println("connection established");
Statement st = conn.createStatement();
String query = "SELECT id, name, job_id, location FROM person WHERE name = 'Tom Swift'";
st.executeQuery(query);