General purpose Table structure in Java (like ResultSet)

Question

Does anyone know if there's a good general-purpose Table-based structure that I can use for manipulating data? ResultSet is an interface, so am I stuck having to fully implement something if I want similar functionality without a database? Apache Commons Collections does not seem to have anything immediately suitable.

Answer 1

Usually you use a List or Set of Javabeans for this. Each Javabean in turn represents one real world entity, like a row in a database. For example an User:

public class User {
    private Long id;
    private String name;
    private Integer age;
    // Add/generate getters+setters.
}

with

List<User> users = new ArrayList<User>();
users.add(new User(1L, "foo", 30));
users.add(new User(2L, "bar", 20));
//...

The List provides methods for fast access by index.

For an undetermined amount of properties (columns) you may consider to use a Map<String, Object> instead where the key represents the property (column) name.

List<Map<String, Object>> table = new ArrayList<Map<String, Object>>();
Map<String, Object> row = new HashMap<String, Object>();
row.put("id", 1L);
row.put("name", "foo");
row.put("age", 30);
table.add(row);
// ...

It only adds a bit more overhead than a simple Javabean since those string keys needs to be stored in the heap as well.

If you don't care about column names, then you can also just go ahead with a List<List<Object>> or maybe even a less flexible Object[][]. With both you can easily access elements by x and y.

Answer 2

Maybe something like the DefaultTableModel will meet your requirements. It is generally used with a JTable to display data but it can be used stand alone.

Or the Bean Table Model based on the RowTableModel has a few more dynamic features that allows you to access rows of data easier.

Answer 3

Why not use an In-Memory Database, such as HSQLDB or H2. They are very lightweight and fast, provide the JDBC interface you seem to want and also provide the JOIN functionality you mention.

Answer 4

Java 6 has a CachedRowSet interface and comes with a Sun class, CachedRowSetImpl. This probably is the closest thing stock out of the box to what you're looking for. It's designed to be populated by a ResultSet.

If that suits you it's probably exactly what you're looking for.

If not, you may have issues populating it properly.