This page provides examples that show how DbUtils may be used.
DbUtils is a very small library of classes so it won't take long
to go through the javadocs
for each class.
The core classes/interfaces in DbUtils are
QueryRunner
and
ResultSetHandler
.
You don't need to know about any other DbUtils classes to benefit from using the
library. The following example demonstrates how these classes are used together.
// Create a ResultSetHandler implementation to convert the // first row into an Object[]. ResultSetHandler h = new ResultSetHandler() { public Object handle(ResultSet rs) throws SQLException { if (!rs.next()) { return null; } ResultSetMetaData meta = rs.getMetaData(); int cols = meta.getColumnCount(); Object[] result = new Object[cols]; for (int i = 0; i < cols; i++) { result[i] = rs.getObject(i + 1); } return result; } }; // Create a QueryRunner that will use connections from // the given DataSource QueryRunner run = new QueryRunner(dataSource); // Execute the query and get the results back from the handler Object[] result = (Object[]) run.query( "SELECT * FROM Person WHERE name=?", "John Doe", h);
You could also perform the previous query using a java.sql.Connection
object
instead of a DataSource
. Notice that you are responsible for closing the
Connection
in this example.
ResultSetHandler h = ... // Define a handler the same as above example // No DataSource so we must handle Connections manually QueryRunner run = new QueryRunner(); Connection conn = ... // open a connection try{ Object[] result = (Object[]) run.query( conn, "SELECT * FROM Person WHERE name=?", "John Doe", h); // do something with the result } finally { // Use this helper method so we don't have to check for null DbUtils.close(conn); }
You can not only fetch data from the database - you can also insert or update data. The following example will first insert a person into the database and after that change the person's height.
QueryRunner run = new QueryRunner( dataSource ); try { // Create an object array to hold the values to insert Object[] insertParams = {"John Doe", new Double( 1.82 )}; // Execute the SQL update statement and return the number of // inserts that were made int inserts = run.update( "INSERT INTO Person (name,height) VALUES (?,?)", insertParams ); // Now it's time to rise to the occation... Object[] updateParams = {new Double( 2.05 ), "John Doe"}; int updates = run.update( "UPDATE Person SET height=? WHERE name=?", updateParams ); } catch(SQLException sqle) { // Handle it }
In the examples above we implemented the ResultSetHandler
interface
to turn the first row of the ResultSet
into an Object[]. This is a
fairly generic implementation that can be reused across many projects.
In recognition of this DbUtils provides a set of ResultSetHandler
implementations in the
org.apache.commons.dbutils.handlers
package that perform common transformations into arrays, Maps, and JavaBeans.
There is a version of each implementation that converts just the first row and
another that converts all rows in the ResultSet
.
We'll start with an example using the BeanHandler
to fetch one
row from the ResultSet
and turn it into a JavaBean.
QueryRunner run = new QueryRunner(dataSource); // Use the BeanHandler implementation to convert the first // ResultSet row into a Person JavaBean. ResultSetHandler h = new BeanHandler(Person.class); // Execute the SQL statement with one replacement parameter and // return the results in a new Person object generated by the BeanHandler. Person p = (Person) run.query( "SELECT * FROM Person WHERE name=?", "John Doe", h);
This time we will use the BeanListHandler to fetch all rows from the
ResultSet
and turn them into a List
of JavaBeans.
QueryRunner run = new QueryRunner(dataSource); // Use the BeanListHandler implementation to convert all // ResultSet rows into a List of Person JavaBeans. ResultSetHandler h = new BeanListHandler(Person.class); // Execute the SQL statement and return the results in a List of // Person objects generated by the BeanListHandler. List persons = (List) run.query("SELECT * FROM Person", h);
Each of the provided ResultSetHandler
implementations accept a
RowProcessor
to do the actual conversion of rows into objects. By default the handlers
use the BasicRowProcessor
implementation but you can implement a custom version to plug in.
Probably the most common customization is to implement the toBean()
method to handle custom database datatype issues.
BasicRowProcessor
uses a BeanProcessor
to convert ResultSet
columns into JavaBean properties. You can
subclass and override processing steps to handle datatype mapping specific to
your application. The provided implementation delegates datatype conversion to
the JDBC driver.
BeanProcessor maps columns to bean properties as documented in the
BeanProcessor.toBean()
javadoc.
Column names must match the bean's property names case insensitively.
For example, the firstname
column would be stored in the bean
by calling its setFirstName()
method. However, many database
column names include characters that either can't be used or are not typically
used in Java method names. You can do one of the following to map
these columns to bean properties:
select social_sec# as socialSecurityNumber from person