ResultSet & ResultSetMetaData Guide

A ResultSet is an interface in Java used to represent the result of a database query, allowing access and manipulation of the query results. ResultSetMetaData is the metadata interface of ResultSet, used to retrieve information about the columns in the ResultSet.

The ResultSetMetaData interface offers several commonly used methods:

1. getColumnCount(): Obtain the number of columns in the ResultSet.
2. Obtain the name of the specified column.
3. Get the label of the specified column.
4. Obtain the data type of the specified column.
5. Get the data type name of the specified column.
6. Check if the specified column is nullable.
7. The function isSigned(int column) is used to determine if the specified column’s data type supports being signed.
8. Obtain the display length of the specified column.
9. Retrieve the precision of the specified column.
10. Retrieve the number of decimal places for the specified column.

ResultSetMetaData can be used to easily obtain information about the columns in a query result, such as generating headers for a table dynamically or processing data based on column data types. Here is an example code using ResultSetMetaData:

ResultSetMetaData rsmd = resultSet.getMetaData();
int columnCount = rsmd.getColumnCount();
for (int i = 1; i <= columnCount; i++) {
    String columnName = rsmd.getColumnName(i);
    String columnType = rsmd.getColumnTypeName(i);
    System.out.println("Column Name: " + columnName);
    System.out.println("Column Type: " + columnType);
}

In the code above, we first use the getMetaData() method to retrieve the metadata object of the ResultSet, then use the getColumnCount() method to get the number of columns. Next, we loop through each column, using the getColumnName() and getColumnTypeName() methods to get the name and data type of each column, and print them out.

It is important to note that column indexes in ResultSetMetaData start from 1, not 0.