How to map a ResultSet with unknown amount of columns to a List and display it in a HTML table?

Question

I have created a Database Application using Netbeans, GlassFish and JavaDB. Now my controller Servlet code executes some dynamic SQL queries and get back a Result Set (or I can ahange toString). Now, how can I show the returned Result Set in a tabular format ( I have no idea about structure of result set). Can anybody help me about this ?

Solution 1

You can use Map<String, Object> to represent a "dynamic" row, which is iterable in <c:forEach>. You can use ResultSetMetaData to collect information about the columns such as the column count and the column labels.

So, this mapping should do:

List<Map<String, Object>> rows = new ArrayList<Map<String, Object>>();
ResultSetMetaData metaData = resultSet.getMetaData();
int columnCount = metaData.getColumnCount();

while (resultSet.next()) {
    Map<String, Object> columns = new LinkedHashMap<String, Object>();

    for (int i = 1; i <= columnCount; i++) {
        columns.put(metaData.getColumnLabel(i), resultSet.getObject(i));
    }

    rows.add(columns);
}

You can display it in JSP as follows:

<table>
  <thead>
    <tr>
      <c:forEach items="${rows[0]}" var="column">
        <td><c:out value="${column.key}" /></td>
      </c:forEach>
    </tr>
  </thead>
  <tbody>
    <c:forEach items="${rows}" var="columns">
      <tr>
        <c:forEach items="${columns}" var="column">
          <td><c:out value="${column.value}" /></td>
        </c:forEach>
      </tr>
    </c:forEach>
  </tbody>
</table>

Solution 2

Use the resultset metadata to know the number of columns returned by the query, the type of these columns, etc.

See the javadoc, which also has an example.

Comments

[alessandro]

Thanks. However, in JSP page I can't see the result set. What I did is as follows: request.setAttribute("als",rows) in my servlet and in JSP, rows = session.getAttribute("als"); - Is anything missing ?

[BalusC]

Just use ${als}. Don't write Java code in JSP file. Your mistake is by the way that you tried to get it as a session attribtue instead of as a request attribute. Read on stackoverflow.com/questions/3177733/… and stackoverflow.com/questions/3106452/…

[alessandro]

Sorry but I add Object rows = request.getAttribute("${als}"). however it showing rows variable not used. And problem remains same.

[BalusC]

That's a warning, not an error. You seem to be not using the scriptlet variable anywhere at all. Just remove those nonsensicial scriptlet <% ... %> lines altogether and use ${als} instead of ${rows} as in <c:forEach items="${als}">, as said in previous comment (and please take some time to read the given links as well before you make more unnecessary mistakes in the future).