用Java连接Java(Connect Java with Mysql)

我试图连接一个Neteans Java项目与Mysql数据库，我无法建立连接，我不知道什么可能出错

我的Java代码：

private void setupLoginEventListener() {

loginBtn.addActionListener(new ActionListener() {

@Override

public void actionPerformed(ActionEvent e) {

rightFirstText = userName.getText();

rightText = password.getPassword();

if (rightFirstText.isEmpty() && rightText.length == 0) {

JOptionPane.showMessageDialog(JavaApplication6.this, "All fields are required", "Error", JOptionPane.ERROR_MESSAGE);

} else if (rightText.length == 0) {

JOptionPane.showMessageDialog(JavaApplication6.this, "Password is required", "Error", JOptionPane.ERROR_MESSAGE);

} else {

try {

conn = getDBConnection();

pst = conn.prepareStatement("select * from pdie where username =? and password=?");

pst.setString(1, rightFirstText);

pst.setString(2, new String(rightText));

rs = pst.executeQuery();

while (rs.next()) {

JOptionPane.showMessageDialog(JavaApplication6.this, "Login Successfull");

}

} catch (SQLException ex) {

JOptionPane.showMessageDialog(JavaApplication6.this, "Login Failed");

}

}

}

});

}

public Connection getDBConnection() {

Connection con = null;

String url = "jdbc:mysql://localhost:3536/";

String dbName = "projectdb";

String driver = "com.mysql.jdbc.Driver";

String connectUserName = "root";

String connectPassword = "";

try {

Class.forName(driver);

con = DriverManager.getConnection(url + dbName, connectUserName, connectPassword);

System.out.println("CONNECTION ESTABLISHED.");

} catch (ClassNotFoundException | SQLException e) {

System.out.println("CONNECTION COULD NOT BE ESTABLISHED.");

}

return con;

}

有任何想法吗？

它给了我这行中空指针异常的错误

pst = conn.prepareStatement("select * from pdie where username =? and password=?");

I am trying to connect a Neteans Java project with Mysql database and i cannot establish a connection and i do not know what could possibly go wrong

My Java code:

private void setupLoginEventListener() {

loginBtn.addActionListener(new ActionListener() {

@Override

public void actionPerformed(ActionEvent e) {

rightFirstText = userName.getText();

rightText = password.getPassword();

if (rightFirstText.isEmpty() && rightText.length == 0) {

JOptionPane.showMessageDialog(JavaApplication6.this, "All fields are required", "Error", JOptionPane.ERROR_MESSAGE);

} else if (rightText.length == 0) {

JOptionPane.showMessageDialog(JavaApplication6.this, "Password is required", "Error", JOptionPane.ERROR_MESSAGE);

} else {

try {

conn = getDBConnection();

pst = conn.prepareStatement("select * from pdie where username =? and password=?");

pst.setString(1, rightFirstText);

pst.setString(2, new String(rightText));

rs = pst.executeQuery();

while (rs.next()) {

JOptionPane.showMessageDialog(JavaApplication6.this, "Login Successfull");

}

} catch (SQLException ex) {

JOptionPane.showMessageDialog(JavaApplication6.this, "Login Failed");

}

}

}

});

}

public Connection getDBConnection() {

Connection con = null;

String url = "jdbc:mysql://localhost:3536/";

String dbName = "projectdb";

String driver = "com.mysql.jdbc.Driver";

String connectUserName = "root";

String connectPassword = "";

try {

Class.forName(driver);

con = DriverManager.getConnection(url + dbName, connectUserName, connectPassword);

System.out.println("CONNECTION ESTABLISHED.");

} catch (ClassNotFoundException | SQLException e) {

System.out.println("CONNECTION COULD NOT BE ESTABLISHED.");

}

return con;

}

any ideas?

it gives me an error for null pointer exception in this line

pst = conn.prepareStatement("select * from pdie where username =? and password=?");

原文：https://stackoverflow.com/questions/27557504

更新时间：2019-12-11 10:06

最满意答案

输入这些行

st=con.createStatement();

String sql="SELECT * FROM TAB";

rs=st.executeQuery(sql);

并尝试打印一个字段; 快速测试问题是否在你准备好的声明中，但可能是在你的conn对象中。

type these lines

st=con.createStatement();

String sql="SELECT * FROM TAB";

rs=st.executeQuery(sql);

and try to print a a field; to test quickly if the problem is in you prepared statement but probably it's in your conn object.

2014-12-19

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