Parse a Database Result Set into an Object List

Question

I am trying to get all data from a table contained in a database, and parse it into a List. I have tried a few different techniques and can't get it working. I am trying to serialize the ResultSet so I can send it over a socket. The code I have got so far is:

public Object readJavaObject(String query, Connection con) throws Exception
{        
    PreparedStatement stmt = con.prepareStatement(query);
    //stmt.setString(1, id);
    query_results = stmt.executeQuery();
    while (query_results.next())
    {
        dataObject = query_results.getObject(1);
    }
    query_results.close();
    stmt.close();

    return dataObject;
}

public void run()
{
    try
    {
        Class.forName(dbClass);
        con = DriverManager.getConnection (dbUrl, user, pass);
        query = "SELECT * FROM Bench_table";
        dataList = (List) this.readJavaObject(query, con);
        con.close();
    }
}

I'm not sure what code to write around readJavaObject . Can anyone help to point out where the issue is?

Thanks for any help.

Answer 1

Take a look at DbUtils (from apache-commons).

If you need a more complex solution for mapping sql results to java objects, take a look at object-relational mapping . In Java the standard is JPA (Java Persistence API), with Hibernate, EclipseLink and OpenJPA as the most famous implementors.

Answer 2

There are several issues with your code.

1. You loop through the results but only return data from the last row. Instead create a List in the readJavaObject method and add an element each pass through the loop.
2. Instead of getting the item in the first column, I assume you want all the data. You are going to have to be more specific with which "get" methods you use to pull data off the ResultSet. Possibly create a POJO to represent a row of data, then inside the loop populate it and store it in the list.
3. Assuming you use a POJO, you might want to use generics with your list to make it easier to get items out of it without having to cast.

Answer 3

I recently discovered the CachedRowSet , which does exactly what OP needs. It notably allows to serialize a ResultSet , and to restore the original when needed.

Answer 4

我不确定您要实现的目标，但是我可以向您介绍DAO（数据访问对象）模式吗？