Can't understand updating process

Question

I have following xhtml document:

  <h:body>
   <ui:composition template="templates/layout.xhtml">
      <ui:define name="content">
        <c:if test="#{sessionBean.userCode > 0}">
          <h:form id="findStudentForm">
            <p:outputPanel id="resultsPanel">
              <c:if test="#{studentsBean.student != null}">
                <h2><h:outputText value="#{studentsBean.student.fullName}"/></h2>
                <h3>Personal data</h3>
                  . . .
                <p align="center">
                <p:commandButton value="Search students" update="@form">
                  <f:setPropertyActionListener value="#{null}" 
                    target="#{studentsBean.student}"/>
                </p:commandButton>
                </p>
              </c:if>
              <c:if test="#{studentsBean.student == null}">
                <h2>Student search</h2>
                  . . .
                <p align="justify">
                  First name
                  <h:inputText value="#{studentsBean.pattern}"/>
                  <p:commandButton value="Поиск" update="resultsPanel"/>                  
                </p>
                <p:dataTable id="resultsTable" var="student" 
                   value="#{studentsBean.studentsList}" 
                             widgetVar="studentsTable" emptyMessage="No records found">
                  . . . 
                  </p:column>
                  <p:column headerText="Actions">
                    <p:commandButton value="Details" update="@form">
                      <f:setPropertyActionListener value="#{student}" 
                        target="#{studentsBean.student}"/>
                    </p:commandButton>
                  </p:column>  
                </p:dataTable>
              </c:if>
            </p:outputPanel>
          </h:form>
        </c:if>
        <c:if test="#{sessionBean.userCode == 0}">
          <ui:include src="templates/include/error.xhtml"/>
        </c:if>
      </ui:define>  
    </ui:composition>
  </h:body>

Also I have following Managed Bean (StudentsBean): . . .

@Named(value = "studentsBean")
@RequestScoped
public class StudentsBean {

  @Inject
  SessionBean session;
  private Student student = null;
  private String pattern = "";
  private String groupName = "";
  @Inject
  private StudentInterface studentProvider;

  . . .

  public String getPattern() {
    return pattern;
  }

  public void setPattern(String pattern) {
    this.pattern = pattern;
  }

  public List<Student> getStudentsList() {
    List<Student> result = new ArrayList<Student>();
    if (studentProvider != null) {
      try {
        result = studentProvider.findStudents(pattern);
      } catch (StudentException e) {
        session.printError(e.getMessage());
      }
    }
    return result;
  }
  . . .

And finally, I have a class StudentsProvider:

public class StudentProvider implements StudentInterface {

  private Connection connection = null;

   . . .

  @Override
  public List<Student> findStudents(String pattern) throws StudentException {
    List<Student> result = new ArrayList<Student>();
    String addon = "";
    if (pattern.trim().isEmpty()) {
      addon = "TOP 10 ";
    }
    try {
      PreparedStatement statement = connection.prepareStatement(
              "SELECT " + addon + "st_pcode, gr_Name, st_FullName "
              + "FROM students, groups WHERE (st_grcode = gr_pcode) AND (st_FullName LIKE ?) "
              + "ORDER BY gr_Name, st_FullName;", ResultSet.TYPE_SCROLL_INSENSITIVE, ResultSet.CONCUR_READ_ONLY);
      statement.setString(1, pattern + "%");
      ResultSet rs = statement.executeQuery();
      while (rs.next()) {
        result.add(getStudent(rs.getString("st_pcode")));
      }
      rs.close();
      statement.close();
    } catch (Exception e) {
      throw new StudentException("Error reading list: " + e.getMessage());
    }
    return result;
  }

  public StudentProvider() throws StudentException {
    try {
    ConnectionProvider provider = new ConnectionProvider();
    connection = provider.getConnection();
    } catch (ConnectionException e) {
      throw new StudentException("Connect error: " + e.getMessage());
    }
  }

  @Override
  public void finalize() throws Throwable {
    connection.close();
    super.finalize();
  }
}

If variable "pattern" an empty string, PreparedStatement returns 10 "first" records. But if the "pattern" has a content - PreparedStatement finds some records. During debug, seems like PreparedStatement works well and returns result set, but no records shows in the re"sultsTable". In additional, I found, that while updating process method

studentProvider.findStudent(pattern)

calling many times. I think, that number of method calls depends of number of records in the "resultsTable".

Before injection, with hard linked objects everything works fine. What's wrong?

By the way, I can't understand one thing. Say, I have a button

<p:commandButton value="Details" update="@form">
    <f:setPropertyActionListener value="#{student}" 
        target="#{studentsBean.student}"/>
</p:commandButton>

in the each record of "resultsTable" (see xhtml listing before for more details). I found, that this button sometimes doesn't work. If resultsTable is empty at the beginning - button doesn't work, but if resultsTable is NOT empty - button work. So how can I make button always working?

Withou reading the whole q' ,datable better be placed inside view or session scope, otherwise it will ne much harder to get it working the right way — Daniel, Oct 16 '12 at 06:32
I solve problem of data missing in the search result. It was an exception, that was badly handeled. I only need to know now - why getter method for dataTable data calls several times? What number of calls depends of and how can I minimize number of calls. — gooamoko, Oct 16 '12 at 08:16
@BalusC Thanks! It's hard for me to think in JSF style yet. I'll remember this golden rule. — gooamoko, Oct 17 '12 at 00:34

score 2 · Accepted Answer · edited May 23 '17 at 12:27

A better way to do this would be (just a sketch):

// an action method in your backing bean.
// This will call your search method and set the values behid your dataTable
public void searchStudents(String pattern) {
    setStudentsList(findStudent(pattern));
}

After the call finished update your dataTable:

<p:commandButton update="resultsTable" action=#{studentProvider.findStudent(pattern)}"

To answer your second question: Why JSF calls getters multiple times, which implies that putting your business logic methods into getters (without lazy loading) seems to be a bad idea (another related question: JSF calling setter & getter multiple times).

Can't understand updating process

1 Answers1