I have a connection manager code as follows:
public class ConnectionManager {
private final String driverName = "com.mysql.jdbc.Driver";
private final String connectionUrl = "jdbc:mysql://localhost:3306/student";
private final String userName = "root";
private final String userPass = "root";
private Connection con = null;
public ConnectionManager() {
try {
Class.forName(driverName);
} catch (ClassNotFoundException e) {
System.out.println(e.toString());
}
}
public Connection createConnection() {
try {
con = DriverManager.getConnection(connectionUrl, userName, userPass);
} catch (SQLException e) {
e.printStackTrace();
}
return con;
}
public void closeConnection() {
try {
this.con.close();
} catch (SQLException e) {
e.printStackTrace();
}
}
}
How can I improve this? I am thinking the following improvement:
) create a connection.properties. What is the best way to implement this? Should I put it the call of the property file on a singleton?
) Make the connection singleton.
Thank you.
If it's for a real application you'd better use a connection pool like this http://commons.apache.org/proper/commons-dbcp/.
Related
this is my connection string for connection postgresql database .And using this code I am able to connect the db
connection = DriverManager.getConnection(
"jdbc:postgresql://127.0.0.1:5433/Test", "youtube",
"1");
Then I am using the same code to retrieve some data .And I get this exception
org.postgresql.util.PSQLException: ERROR: "userdetail" NOT EXIST
Position: 27
which referr this line
con=GetDbConn();
So mytable name is UserDetail not userdetail I dont understand why am i getting this exception message
And this is my code
public class DbUtils {
private static final String DB_DRIVER="org.postgresql.Driver";
private static final String DB_CONN="jdbc:postgresql://127.0.0.1:5433/Test";
private static final String DB_USER="youtube";
private static final String DB_PASS="1";
public void SelectUserDetails() {
Connection con=null;
Statement statement;
String query="select isim,soyisim from UserDetail";
try {
con=GetDbConn();
statement= con.createStatement();
ResultSet resultSet=statement.executeQuery(query);
while(resultSet.next()){
String isimM=resultSet.getString("isim");
String soyisimM=resultSet.getString("soyisim");
System.out.println("isim :"+soyisimM+" soyisim: "+soyisimM);
}
} catch (SQLException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
private static Connection GetDbConn() {
Connection con = null;
try {
Class.forName(DB_DRIVER);
con=DriverManager.getConnection(DB_CONN, DB_USER, DB_PASS);
} catch (ClassNotFoundException e) {
e.printStackTrace();
} catch (SQLException e) {
e.printStackTrace();
}
return con;
}
}
private static String dbURL = "jdbc:mysql://localhost:3306/mydb";
private static String username = "secret";
private static String password = "secret";
private static Connection conn = null;
public static void initDbConnection(){
try {
conn = DriverManager.getConnection(dbURL, username, password);
Class.forName("com.mysql.jdbc.Driver");
} catch (SQLException e1) {
e1.printStackTrace();
}
catch (ClassNotFoundException e) {
e.printStackTrace();
}
}
public static void test3(){
initDbConnection();
try{
String sql = "SELECT * FROM Products";
Statement statement = conn.createStatement();
ResultSet result = statement.executeQuery(sql);
while (result.next()){
String name = result.getString("name");
System.out.println(name);
}
}
catch (SQLException ex) {
ex.printStackTrace();
}
}
Why I'm getting null pointer exception on conn even though I called the initDbConnection() on test3() ? How will I elimate this problem?
Class.forName("com.mysql.jdbc.Driver");
should be the first line. As this load the mysql driver in the memory. Then you will acquire the connection.
So it should be
try {
Class.forName("com.mysql.jdbc.Driver");
conn = DriverManager.getConnection(dbURL, username, password);
} catch (SQLException e1) {
e1.printStackTrace();
}
catch (ClassNotFoundException e) {
e.printStackTrace();
}
i'm trying to establish connection with mysql database through file properties and then run the information from servlet. my Connection class looks like this:
public class pageDao {
private Connection connection;
private Statement statement;
private pageDao() {
Properties prop = new Properties();
try {
//Class.forName("oracle.jdbc.driver.OracleDriver");
//Class.forName("org.gjt.mm.mysql.Driver");
Class.forName("com.mysql.jdbc.Driver");
} catch (ClassNotFoundException cnfe) {
System.out.println("Error loading driver: " +cnfe);
}
try {
try {
//load a properties file
prop.load(new FileInputStream("config.properties"));
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
String db = prop.getProperty("database");
String dbuser = prop.getProperty("dbuser");
String dbpassword = prop.getProperty("dbpassword");
connection = DriverManager.getConnection(db,dbuser,dbpassword);
} catch (SQLException e) {
e.printStackTrace();
}
}
private static pageDao thisDao;
public static pageDao gedDao()
{
if(thisDao == null)
thisDao = new pageDao();
return thisDao;
}
public PageData getPage(String id)
{
PageData data = new PageData();
try {
statement = connection.createStatement();
ResultSet rs = statement.executeQuery("select * from pages where id='"+id+"'");
if(rs.next())
{
data.setId(rs.getString("id"));
data.setParentid(rs.getString("parentid"));
data.setTitle(rs.getString("title"));
data.setTitle4menu(rs.getString("title4menu"));
data.setKeywords(rs.getString("keywords"));
data.setDescription(rs.getString("description"));
data.setMaintext(rs.getString("maintext"));
}
else
return null;
} catch (SQLException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
return data;
}
when i run it, it doesn't show the mistake that connection wasn't established, but when it gets to the
public PageData getPage(String id) {
PageData data = new PageData();
try {
statement = connection.createStatement();
it throws java.lang.NullPointerException.
can anybody help me out with that?
there is no issue with code.
check your passing parameter ...
check sample
private Connection getConnection() {
try {
String dbUrl = "jdbc:mysql://localhost:3306/projectmining";
Class.forName("com.mysql.jdbc.Driver");
return DriverManager.getConnection(dbUrl, "root", "admin");
} catch (Exception ex) {
ex.printStackTrace();
}
return null;
}
I am getting this message in unit test expected:<interface java.sql.Connection> but was:<class com.mysql.jdbc.JDBC4Connection>
from my code:
#Test
public void connectionTest() throws SQLException{
Connection conn = ConnectionManager.createConnection();
assertEquals(Connection.class, conn.getClass());
conn.close();
}
My mock class for getting connection:
public class ConnectionManager {
#SuppressWarnings("unused")
public static Connection createConnection() throws SQLException {
String url = "jdbc:mysql://localhost:3306/library";
String name = "root";
String password = "root";
Connection connection = null;
try {
Class.forName("com.mysql.jdbc.Driver");
connection = DriverManager.getConnection(url, name, password);
} catch (ClassNotFoundException e) {
if (connection != null){
connection.close();
}
throw new SQLException(e);
}
return connection;
}
}
What is wrong with my code?
Your assert is fundamentally wrong.
Connection.class is an interface.
conn.getClass() will return a concrete class that implements that interface.
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;
}
}
}