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I'm working on a JSF database management system project using Primefaces and I'm currently trying to create a page that has two data selection tables. There will be two different data tables in the page, from one of them user will be able to select multiple data while from the other one user can only select one. After the selection backing bean takes the needed values from both of the selected rows and creates a new data for a third different table. The third different table is also available in the page as a data table with no selection. Unfortunately in my design the backing bean cannot take the value of the selected row of the second data table while it successfully takes multiple selected rows from the first table. Here is my code:

This is the xhtml code for the page:

 <html xmlns="http://www.w3.org/1999/xhtml"
    xmlns:h="http://java.sun.com/jsf/html"
    xmlns:f="http://java.sun.com/jsf/core"
    xmlns:p="http://primefaces.org/ui">
    <h:head>

    <title>Ogrenci-Ders Atama Sayfasi</title>
    </h:head>

    <h:body>
    <h:form id="form">
        <h:outputText id="msgcomponent" binding="#{msgBean.component}" />
        <p:messages showDetail="true" showSummary="true" autoUpdate="true" />

        <p:dataTable id="lessonTable" var="lesson"
            value="#{lessonView.lessons}" selectionMode="multiple"
            selection="#{StudentLessonBean.selectedLessons}"
            rowKey="#{lesson.lessonId}" scrollable="true" scrollHeight="150">



            <f:facet name="header">
            Dersler
        </f:facet>
            <p:column headerText="Id">
                <h:outputText value="#{lesson.lessonId}" />
            </p:column>
            <p:column headerText="Name">
                <h:outputText value="#{lesson.lessonName}" />
            </p:column>
        </p:dataTable>
    </h:form>

    <h:form id="studentTableForm">
        <p:dataTable id="studentTable" var="student"
            value="#{studentView.students}" selectionMode="single"
            selection="#{StudentLessonBean.selectedStudent}"
            rowKey="#{student.studentId}" scrollable="true" scrollHeight="150">

            <f:facet name="header">
            Öğrenciler
        </f:facet>
            <p:column headerText="Id">
                <h:outputText value="#{student.studentId}" />
            </p:column>
            <p:column headerText="Number">
                <h:outputText value="#{student.studentNumber}" />
            </p:column>
            <p:column headerText="Name">
                <h:outputText value="#{student.studentName}" />
            </p:column>
            <p:column headerText="Class">
                <h:outputText value="#{student.studentClass}" />
            </p:column>

        </p:dataTable>
    </h:form>

    <p:commandButton icon="ui-icon-arrowthick-2-e-w"
        action="#{StudentLessonBean.InsertStudentLesson()}">
    </p:commandButton>

    <h:form id="kullanilmayan">
        <p:dataTable var="studentLesson"
            value="#{StudentLessonBean.studentLessons}"
            widgetVar="studentLessonsTable"
            emptyMessage="No students found with given criteria"
            filteredValue="#{StudentLessonBean.filteredStudentLessons}">

            <f:facet name="header">
                <p:outputPanel>
                    <h:outputText value="Search all fields:" />
                    <p:inputText id="globalFilter"
                        onkeyup="PF('studentLessonsTable').filter()" 
           style="width:150px"
                        placeholder="Enter keyword" />
                </p:outputPanel>
            </f:facet>

            <p:column filterBy="#{studentLesson.studentLessonId}"
                headerText="Student-Lesson Id" footerText="contains"
                filterMatchMode="contains">
                <h:outputText value="#{studentLesson.studentLessonId}" />
            </p:column>

            <p:column filterBy="#{studentLesson.studentId}"
                headerText="Student Id" footerText="contains"
                filterMatchMode="contains">
                <h:outputText value="#{studentLesson.studentId}" />
            </p:column>

            <p:column filterBy="#{studentLesson.lessonId}" headerText="Lesson Id"
                footerText="contains" filterMatchMode="contains">
                <h:outputText value="#{studentLesson.lessonId}" />
            </p:column>

            <p:column filterBy="#{studentLesson.score}" headerText="Score"
                footerText="contains" filterMatchMode="contains">
                <h:outputText value="#{studentLesson.score}" />
            </p:column>

        </p:dataTable>
    </h:form>
</h:body>
</html>

Here is the bean for getting the selected rows and use them to insert a new data to a third different table (the problem is right here, the program never runs the setSelectedStudent() function eventually leaving it null and throwing a nullpointerexception when it tries to get the selected row's id):

package bean;

import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.ArrayList;
import java.util.List;

import javax.faces.bean.ManagedBean;
import javax.faces.bean.RequestScoped;

import dao.StudentLessonInsertion;
import egeproject.ConnectionClass;
import model.Lesson;
import model.Student;
import model.StudentLesson;

@ManagedBean(name = "StudentLessonBean")
@RequestScoped

public class StudentLessonBean {

    StudentLessonInsertion studentLessonInsertion;
    List<Lesson> selectedLessons;
    List<StudentLesson> studentLessons;
    List<StudentLesson> filteredStudentLessons;
    Student selectedStudent;

    public List<Lesson> getSelectedLessons() {
        return selectedLessons;
    }

    public void setSelectedLessons(List<Lesson> selectedLessons) {
        this.selectedLessons = selectedLessons;
    }

    public Student getSelectedStudent() {
        return selectedStudent;
    }

    public void setSelectedStudent(Student selectedStudent) {
        this.selectedStudent = selectedStudent;
    }

    public void InsertStudentLesson() throws SQLException {
        studentLessonInsertion = new StudentLessonInsertion();
        StudentLesson studentLesson = new StudentLesson();
        for (int i = 0; i < selectedLessons.size(); i++) {
            studentLesson.setLessonId(selectedLessons.get(i).getLessonId());
            studentLesson.setStudentId(selectedStudent.getStudentId());
            studentLessonInsertion.InsertStudentLesson(studentLesson);
            studentLesson.clear();
        }

    }

    public List<StudentLesson> getFilteredStudentLessons() {
        return filteredStudentLessons;
    }

    public void setFilteredStudentLessons(List<StudentLesson> filteredStudentLessons) {
        this.filteredStudentLessons = filteredStudentLessons;
    }

    public List<StudentLesson> getStudentLessons() throws SQLException {
        studentLessons = new ArrayList<StudentLesson>();
        ConnectionClass connectionClass = new ConnectionClass();
        Connection connection = connectionClass.getDBConnection();

        String selectionSql = "SELECT \"Student_Id\", \"Lesson_Id\", \"Score\", \"Student_Lesson_Id\"\r\n"
                + "  FROM public.\"Student_Lesson_Table\";\r\n" + "";
        try {
            PreparedStatement preparedStatement = connection.prepareStatement(selectionSql);
            ResultSet results = preparedStatement.executeQuery();
            while (results.next()) {
                StudentLesson newStudentLesson = new StudentLesson();
                newStudentLesson.setStudentId(results.getInt("Student_Id"));
                newStudentLesson.setLessonId(results.getInt("Lesson_Id"));
                newStudentLesson.setScore(results.getInt("Score"));
                newStudentLesson.setStudentLessonId(results.getInt("Student_Lesson_Id"));
                studentLessons.add(newStudentLesson);
            }
        } catch (SQLException e) {

            e.printStackTrace();
            System.out.println(e);
        } finally {
            connection.close();
        }

        return studentLessons;

    }


}

Here are the models of the used classes:

Student Model:

package model;

import javax.faces.bean.ManagedBean;
import javax.faces.bean.RequestScoped;

import egeproject.StudentView;

@ManagedBean(name = "Student")
@RequestScoped

public class Student {

    private Integer studentId;
    private Integer studentNumber;
    private String studentName;
    private String studentClass;

    public Integer getStudentNumber() {
        return studentNumber;
    }
    public void setStudentNumber(Integer studentNumber) {
        this.studentNumber = studentNumber;
    }
    public String getStudentName() {
        return studentName;
    }
    public void setStudentName(String studentName) {
        this.studentName = studentName;
    }
    public String getStudentClass() {
        return studentClass;
    }
    public void setStudentClass(String studentClass) {
        this.studentClass = studentClass;
    }

    public Student createStudent(int studentNumber, String studentName, String studentClass)
    {
        this.setStudentNumber(studentNumber);
        this.setStudentName(studentName);
        this.setStudentClass(studentClass);
        return this;
    }

    public Student returnStudent()
    {
        return this;
    }

    public Integer getStudentId() {
        return studentId;
    }
    public void setStudentId(Integer studentId) {
        this.studentId = studentId;
    }

    public void clear()
    {
        this.studentId = null;
        this.studentClass = null;
        this.studentName = null;
        this.studentNumber = null;
    }
}

Lesson Model:

package model;

import javax.faces.bean.ManagedBean;
import javax.faces.bean.RequestScoped;

@ManagedBean(name = "Lesson")
@RequestScoped

public class Lesson {

    private Integer lessonId;
    private String lessonName;


    public String getLessonName() {
        return lessonName;
    }
    public void setLessonName(String lessonName) {
        this.lessonName = lessonName;
    }

    public Lesson createLesson(String lessonName) {
        this.setLessonName(lessonName);
        return this;
    }
    public Integer getLessonId() {
        return lessonId;
    }
    public void setLessonId(int lessonId) {
        this.lessonId = lessonId;
    }

    public Lesson returnLesson()
    {
        return this;
    }

    public void clear()
    {
        lessonId = null;
        lessonName = null;
    }
}

Student Lesson Model:

package model;
import javax.faces.bean.ManagedBean;
import javax.faces.bean.RequestScoped;

@ManagedBean(name = "StudentLesson")
@RequestScoped

public class StudentLesson {

    private Integer studentLessonId;
    private Integer studentId;
    private Integer lessonId;
    private Integer score;


    public Integer getStudentLessonId() {
        return studentLessonId;
    }
    public void setStudentLessonId(Integer studentLessonId) {
        this.studentLessonId = studentLessonId;
    }
    public Integer getStudentId() {
        return studentId;
    }
    public void setStudentId(Integer studentId) {
        this.studentId = studentId;
    }
    public Integer getLessonId() {
        return lessonId;
    }
    public void setLessonId(Integer lessonId) {
        this.lessonId = lessonId;
    }
    public Integer getScore() {
        return score;
    }
    public void setScore(Integer score) {
        this.score = score;
    }

    public StudentLesson createReturn(Student student, Lesson lesson)
    {
        this.lessonId = lesson.getLessonId();
        this.studentId = student.getStudentId();
        return this;
    }

    public void clear()
    {
        this.lessonId=null;
        this.score=null;
        this.studentId=null;
        this.studentLessonId=null;
    }

}

Here is the full stack trace:

WARNING: #{StudentLessonBean.InsertStudentLesson()}: java.lang.NullPointerException
javax.faces.FacesException: #{StudentLessonBean.InsertStudentLesson()}: java.lang.NullPointerException
    at com.sun.faces.application.ActionListenerImpl.processAction(ActionListenerImpl.java:118)
    at javax.faces.component.UICommand.broadcast(UICommand.java:315)
    at javax.faces.component.UIViewRoot.broadcastEvents(UIViewRoot.java:794)
    at javax.faces.component.UIViewRoot.processApplication(UIViewRoot.java:1259)
    at com.sun.faces.lifecycle.InvokeApplicationPhase.execute(InvokeApplicationPhase.java:81)
    at com.sun.faces.lifecycle.Phase.doPhase(Phase.java:101)
    at com.sun.faces.lifecycle.LifecycleImpl.execute(LifecycleImpl.java:118)
    at javax.faces.webapp.FacesServlet.service(FacesServlet.java:593)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:231)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
    at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:198)
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:96)
    at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:478)
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:140)
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:80)
    at org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:624)
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:87)
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:342)
    at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:799)
    at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:66)
    at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:868)
    at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1455)
    at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
    at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
    at java.lang.Thread.run(Unknown Source)
Caused by: javax.faces.el.EvaluationException: java.lang.NullPointerException
    at javax.faces.component.MethodBindingMethodExpressionAdapter.invoke(MethodBindingMethodExpressionAdapter.java:102)
    at com.sun.faces.application.ActionListenerImpl.processAction(ActionListenerImpl.java:102)
    ... 29 more
Caused by: java.lang.NullPointerException
    at bean.StudentLessonBean.InsertStudentLesson(StudentLessonBean.java:51)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
    at java.lang.reflect.Method.invoke(Unknown Source)
    at org.apache.el.parser.AstValue.invoke(AstValue.java:247)
    at org.apache.el.MethodExpressionImpl.invoke(MethodExpressionImpl.java:267)
    at com.sun.faces.facelets.el.TagMethodExpression.invoke(TagMethodExpression.java:105)
    at javax.faces.component.MethodBindingMethodExpressionAdapter.invoke(MethodBindingMethodExpressionAdapter.java:88)
    ... 30 more

Thank you, sincerely :) Happy coding

Kukeltje
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BeetleJuice
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  • please add full stack trace – Ori Marko Jul 26 '17 at 06:26
  • Sure, added the full stack trace, thank you – BeetleJuice Jul 26 '17 at 06:39
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    selectedLessons probably null, when do you set it? – Ori Marko Jul 26 '17 at 06:42
  • Start by using a more modern tutorial. SQL in managed beans is **wrong** practice. It (over) simplifies things for tutorials. Use JPA, use entities Read https://stackoverflow.com/questions/30639785/jsf-controller-service-and-dao and https://stackoverflow.com/questions/10301363/jpa-entity-as-jsf-bean – Kukeltje Jul 26 '17 at 06:49
  • selectedLessons get set when the rows are selected, setSelectedLessons get invoked by selection="#{StudentLessonBean.selectedLessons}", however selectedStudent doesn't get set and stays null which throws the exception. – BeetleJuice Jul 26 '17 at 06:52
  • @Kukeltje I currently need to solve this problem, but appreciate your advise, noted. Thank you – BeetleJuice Jul 26 '17 at 06:57
  • https://stackoverflow.com/questions/7031885/how-to-choose-the-right-bean-scope. Looks like you need to take a step back and learn some more basics about jsf, including doing 'new' on 'managed beans'... – Kukeltje Jul 26 '17 at 07:21
  • I really want to learn more basics about jsf and I know my code is full of imperfections but I really need to solve this problem and I can't really understand the reason I'm having this spesific problem or relate it to the bad structure. – BeetleJuice Jul 26 '17 at 08:05
  • Waiting some wizard to spawn and solve the case – BeetleJuice Jul 26 '17 at 10:52
  • Why do have so many in xhtml code? and your is not even inside one of these forms. Try using one and see what happens. – Tonkichi Jul 28 '17 at 06:07
  • @Tonkichi the problem is just solved with this, thank you so much – BeetleJuice Jul 31 '17 at 06:04

1 Answers1

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The problem is solved by collecting all tables and the button in the same form. I actually tried that before but the page wasn't loading apparently because of a "Spring java.lang.IllegalStateException: Cannot create a session after the response has been committed" issue. Many thanks to Tonkitchi (https://stackoverflow.com/users/8079165/tonkichi) for clearing out the problem.

BeetleJuice
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