Learn Java: Java JDBC FAQ: How do I determine the number of columns in a ResultSet?

When you send a SELECT statement to a database using JDBC, you'll read the query results into a ResultSet object. We demonstrated how to do this in our article on Creating and Executing an SQL Query.

In many database programs you'll need to go a bit further, and dynamically determine the number of columns that are in a ResultSet object. As an example, I've been working on a Contact Management servlet-based Intranet application. Because I can dynamically determine the number of columns returned from my queries, I can write one QueryServlet to handle all of my database query needs. This makes it very easy to create a simple report writer for my Intranet app!

You can get information about your ResultSet object, including the number of columns of data in the ResultSet, by creating a ResultSetMetaData object, and using it's methods to extract the desired information from the ResultSet object. Here's how to determine the number of columns in a ResultSet object:

    //------------------------------------------------------//
    //  Here's the code to determine the number of columns  //
    //  in the ResultSet.                                   //
    //------------------------------------------------------//
    Statement st = conn.createStatement();
    ResultSet rs = st.executeQuery("SELECT * from Customer");
    ResultSetMetaData rsmd = rs.getMetaData();

    int numCols = rsmd.getColumnCount();

In this example, the variable numCols contains the number of columns of data that are in the ResultSet.

As a final note, once you know the number of columns that are in a ResultSet, you can use the next() method of the ResultSet object to cycle through the columns and the ResultSet data.

Question:	How do I determine the number of columns in a ResultSet?
Answer:

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