tut_sources.apt

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                                    ------------------------------
                                            Data sources
                                    ------------------------------
                                          Fabrizio Giustina
                                    ------------------------------
                                              11-11-2005
                                    ------------------------------

Data sources

* Expressions

   Up until this point, we have simply had a List object available to
   us under the name "list" in the request scope that has driven the
   display of the tables shown. We have been setting up that bean with
   the following scriptlet, but presumably you would be doing something
   similar in your Action class rather then raw on this jsp page.

+-------------------------------------------------------------------+
<% request.setAttribute( "test", new TestList( 10 ) ); %>
+-------------------------------------------------------------------+

   This table is called with the following attributes:

+-------------------------------------------------------------------+
<display:table name="test">
+-------------------------------------------------------------------+

   You can also acquire a handle to the list you want to display by
   specifying not only a bean name, but also a bean property (a getter
   method), and the table tag will call that property to fetch the list
   to display.

   Actually there are two "flavors" of displaytag: an EL version, which
   requires j2ee 1.3 and a jsp 1.1 (j2ee 1.2 compatible) version

   In the EL version you can obviously use an EL expression, like
   name="${pageScope.name.property}"

   In the non-EL version you can define the "name" attribute using a
   really similar sintax, just without the ${}:

   You can define the scope of the bean adding one of the following
   suffix:

     * pageScope

     * requestScope (default)

     * sessionScope

     * applicationScope

     []

   You can also access javabean style properties, mapped properties or
   indexed properties in the bean, also nested. The syntax for
   accessing a javabean property is .property . You can read a mapped
   property specifying it between () and an indexed property using [].

   So the following:

----------------------------------------------------------------------
   sessionScope.list.value.attribute(name).item[1]
----------------------------------------------------------------------

   is equivalent to:

----------------------------------------------------------------------
   session.getAttribute("list").getValue().getAttribute("name").getItem(1)
----------------------------------------------------------------------

* Supported data

   The table tag actually supports the following kind of objects:

     * a Collection

     * an Enumeration

     * a Map (values are displayed in row)

     * a Dictionary (values are displayed in row)

     * an array

     * an Iterator

     * any Object with an iterator() method

     * ... any other object will be displayed on a single row

     []


* From a db?

   Displaytag will never support retrieving data from a db directly.
   Displaytag is here to help you in displaying data, not to retrieve
   them.

   Anyway, there are a couple of easy methods to get records from a db
   and display them using displaytag:

   1) Using jstl:

   just use the sql:query tag and pass the result to the table tag in
   this way

+-------------------------------------------------------------------+
        <sql:query var="results">
          select * from table
        </sql:query>

        <display:table name="${results.rows}" />

        (or
        <display:table name="pageScope.results.rows" />
        if not using the EL version)
+-------------------------------------------------------------------+

   2) Using dynabeans

   see {{{http://jakarta.apache.org/commons/beanutils/api/org/apache/commons/beanutils/RowSetDynaClass.html}}}

+-------------------------------------------------------------------+
<%
      Connection con = ...; // just open a connection

      Statement stmt = con.createStatement();
      ResultSet rs = stmt.executeQuery("SELECT * from table");
      RowSetDynaClass resultSet = new RowSetDynaClass(rs, false);
      stmt.close();
      con.close();
      request.setAttribute("results", resultSet);
%>

      <display:table name="requestScope.results.rows" />
+-------------------------------------------------------------------+