Java: try-catch MySQL exception

Question

I'm encountering errors when connecting to MySQL from Java, so I'm wrapping the connection establishment in a try statement. However, doing this means that any attempt to use the Connection variable afterwards throws a variable conn might not have been initialized error. What is the proper way to do this? What I have:

Connection conn;
try {
    conn = DriverManager.getConnection("jdbc:mysql://localhost:3306/database", "alexis","pass");
}
catch (SQLException e) {
    System.err.println("SQL exception: " + e.getMessage());
    System.exit(1);
}
if (!conn.isClosed()) {
    conn.close();
}

Error:

> variable conn might not have been initialized

SoftMolina · Accepted Answer · 2017-02-23 22:44:21Z

1

The variable con is accessible outside of the try/catch but the compiler is smart enough to recognize that it is possible that con might never be assigned a value, not even null. Local variables are not automatically null like instance variables. The easiest thing to address that is to change.

Connection con;

to

Connection con = null;

answered Feb 23, 2017 at 22:44

SoftMolina

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Comments

Remy Cilia · Accepted Answer · 2017-02-23 22:37:52Z

0

You should declare your object like this:

Connection conn = null;

And then make sure it's not null before you use it:

if (conn != null && !conn.isClosed()) {
    conn.close();
}

answered Feb 23, 2017 at 22:37

Remy Cilia

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Comments

Haifeng Zhang · Accepted Answer · 2017-02-23 22:53:45Z

Connection conn;  //was declared without initializing any value. You encountered error when try to use an uninitialized connection instance
Connection conn = null; // declared & initialized

Code:

Connection conn = null;  // initialize conn with null value
try {
    conn = DriverManager.getConnection("jdbc:mysql://localhost:3306/database", "alexis","pass");
}
catch (SQLException e) {
    System.err.println("SQL exception: " + e.getMessage());
    System.exit(1);
}
finally{
    if (conn !=null && !conn.isClosed()) { // validate conn whether it is null 
        conn.close();
    }
}

Alternatively, you can use try-with-resources which can close connection automatically.

  try (Connection conn = DriverManager.getConnection(CONNECTION_URL);
PreparedStatement ps = con.prepareStatement(sqlStrQuery);){
        // execution code here..
    }catch(SQLException sqle){
        // do something
    }

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