1. Overview
In this article, we’re reviewing the JDBC RowSet interface. A JDBC RowSet object holds tabular data in a style that makes it more adaptable and simpler to use than a result set.
Oracle has defined five RowSet interfaces for the most frequent uses of a RowSet:
- JdbcRowSet
- CachedRowSet
- WebRowSet
- JoinRowSet
- FilteredRowSet
In this tutorial, we’ll review how to use these RowSet interfaces.
2. JdbcRowSet
Let’s start with the JdbcRowSet – we’ll simply create one setting up the URL, username and the password for the connection to the database:
JdbcRowSet jdbcRS = RowSetProvider.newFactory().createJdbcRowSet();
jdbcRS.setUrl("jdbc:h2:mem:testdb");
jdbcRS.setUsername("sa");
jdbcRS.setPassword("");
jdbcRS.setType(ResultSet.TYPE_SCROLL_INSENSITIVE);
String sql = "SELECT * FROM customers";
jdbcRS.setCommand(sql);
jdbcRS.execute();
jdbcRS.addRowSetListener(new ExampleListener());
while (jdbcRS.next()) {
// each call to next, generates a cursorMoved event
System.out.println("id = " + jdbcRS.getString(1));
System.out.println("name = " + jdbcRS.getString(2));
}
In the above example, jdbcRs contained no data until we defined the SQL statement with the method setCommand and then ran the method execute.
Also notice how, in order to perform event handling, we added a RowSetListener into the JdbcRowSet.
JdbcRowSet is different than the other four RowSet implementations – because it’s always connected to the database and because of this it’s most similar to the ResultSet object.
3. CachedRowSet
A CachedRowSet object is unique because it can operate without being connected to its data source. We call this a “disconnected RowSet object”.
CachedRowSet gets its name due to the fact it caches its data in memory so that it can operate on its own data instead of the data stored in a database.
As CachedRowSet interface is the super interface for all disconnected RowSet objects, the code we review below is also applicable to a WebRowSet, JoinRowSet, or FilteredRowSet just as well:
CachedRowSet crs = RowSetProvider.newFactory().createCachedRowSet();
crs.setUsername(username);
crs.setPassword(password);
crs.setUrl(url);
crs.setCommand(sql);
crs.execute();
crs.addRowSetListener(new ExampleListener());
while (crs.next()) {
if (crs.getInt("id") == 1) {
System.out.println("CRS found customer1 and will remove the record.");
crs.deleteRow();
break;
}
}
4. WebRowSet
Next, let’s have a look at the WebRowSet.
This is also unique because, in addition to offering the capabilities of a CachedRowSet object, it can write itself to an XML document and can also read that XML document to convert itself back to a WebRowSet:
WebRowSet wrs = RowSetProvider.newFactory().createWebRowSet();
wrs.setUsername(username);
wrs.setPassword(password);
wrs.setUrl(url);
wrs.setCommand(sql);
wrs.execute();
FileOutputStream ostream = new FileOutputStream("customers.xml");
wrs.writeXml(ostream);
Using the writeXml method, we write the current state of a WebRowSet object to an XML document.
By passing the writeXml method an OutputStream object, we write in bytes instead of characters, which can be quite helpful to handle all forms of data.
5. JoinRowSet
JoinRowSet lets us create a SQL JOIN between RowSet objects when these are in memory. This is significant because it saves us the overhead of having to create one or more connections:
CachedRowSet customers = RowSetProvider.newFactory().createCachedRowSet();
// configuration of settings for CachedRowSet
CachedRowSetImpl associates = new CachedRowSetImpl();
// configuration of settings for this CachedRowSet
JoinRowSet jrs = new JoinRowSetImpl();
jrs.addRowSet(customers,ID);
jrs.addRowSet(associates,ID);
Because each RowSet object added to a JoinRowSet object needs a match column, the column on which the SQL JOIN is based, we specify “id” in the addRowSet method.
Note that, rather than using the column name, we could have also used the column number.
6. FilteredRowSet
Finally, the FilteredRowSet lets us cut down the number of rows that are visible in a RowSet object so that we can work with only the data that is relevant to what we are doing.
We decide how we want to “filter” the data using an implementation of the Predicate interface:
public class FilterExample implements Predicate {
private Pattern pattern;
public FilterExample(String regexQuery) {
if (regexQuery != null && !regexQuery.isEmpty()) {
pattern = Pattern.compile(regexQuery);
}
}
public boolean evaluate(RowSet rs) {
try {
if (!rs.isAfterLast()) {
String name = rs.getString("name");
System.out.println(String.format(
"Searching for pattern '%s' in %s", pattern.toString(),
name));
Matcher matcher = pattern.matcher(name);
return matcher.matches();
} else
return false;
} catch (Exception e) {
e.printStackTrace();
return false;
}
}
// methods for handling errors
}
Now we apply that filter to a FilteredRowSet object:
RowSetFactory rsf = RowSetProvider.newFactory();
FilteredRowSet frs = rsf.createFilteredRowSet();
frs.setCommand("select * from customers");
frs.execute(conn);
frs.setFilter(new FilterExample("^[A-C].*"));
ResultSetMetaData rsmd = frs.getMetaData();
int columncount = rsmd.getColumnCount();
while (frs.next()) {
for (int i = 1; i <= columncount; i++) {
System.out.println(
rsmd.getColumnLabel(i)
+ " = "
+ frs.getObject(i) + " ");
}
}
7. Conclusion
This quick tutorial covered the five standard implementations of the RowSet interface available in the JDK.
We discussed the configuration of each implementation and mentioned the differences between them.
As we pointed out, only one of the RowSet implementations is a connected RowSet object – the JdbcRowSet. The other four are disconnected RowSet objects.
And, as always, the full code for this article can be found over on Github.
