从PostgreSQL

Question

我在PostgreSQL中创建了这个简单的表：

CREATE TABLE "User"(
 "id" Integer NOT NULL,
 "user_name" Text,
 "first_name" Text,
 "last_name" Text,
 "last_login" Date,
 "date_registered" Date,
 "role" Integer,
 "can_login" Integer
)
;

-- Add keys for table User

ALTER TABLE "User" ADD CONSTRAINT "Key1" PRIMARY KEY ("id")
;

我尝试从Tomcat servlet

创建简单的查询代码

@Resource(name = "jdbc/DefaultDB")
    private DataSource ds;

    public void databaseQuery() throws SQLException
    {
        if (ds == null)
        {
            throw new SQLException("Can't get data source");
        }
        Connection conn = ds.getConnection();

        if (conn == null)
        {
            throw new SQLException("Can't get database connection");
        }

        PreparedStatement ps = null;

        try
        {
            ps = conn.prepareStatement("SELECT * FROM USER");

//            ps.setString(1, user);
            // Get data from Oracle Database
            ResultSet result = ps.executeQuery();
            while (result.next())
            {
                System.out.println(">>>>> value " + result);
            }
        }
        finally
        {
            if (ps != null)
            {
                ps.close();
            }
            conn.close();
        }
    }

但是在插入一些测试数据之后没有任何反应。使用Java代码从PostgreSQL获取数据的正确方法是什么？