General purpose Table structure in Java (like ResultSet) [duplicate]

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Table like java data structure

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 implem开发者_JAVA技巧ent something if I want similar functionality without a database? Apache Commons Collections does not seem to have anything immediately suitable.

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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.

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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.

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Google Guava libraries offer several general purpose Table implementations - HashBasedTable, TreeBasedTable. The classes are generic so any class can act as a row/column key.

Example from the docs:

Table<Vertex, Vertex, Double> weightedGraph = HashBasedTable.create();
weightedGraph.put(v1, v2, 4.0);
weightedGraph.put(v1, v3, 20.0);
weightedGraph.put(v2, v3, 5.0);

weightedGraph.row(v1); // returns a Map mapping v2 to 4, v3 to 20
weightedGraph.column(v3); // returns a Map mapping v1 to 20, v2 to 5

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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.

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