[FIXED] DropDownlist how to load the data using Spring boot Mysql

Issue

i am beginner of spring boot and mysql. i need to load DropDownList. i don't know how to load them.what tried so far i attached below.i want load the student name on the dropdown.

index.html- DropDown load

 <select class="form-control" name="example" id="example">
         <option value="0">ALL</option>
         <option th:each="Student : ${allStudents}"
                 th:value="${Student.id}"
                 th:selected="${Student.isSelected(lastselected)}"
                 th:text="${Student.studentname}">
         </option>
    </select>

Student Class

package com.example.StudentCrud.domain;

import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;

@Entity
public class Student {
    @Id
    @GeneratedValue(strategy= GenerationType.IDENTITY)
    private Long id;
    private String studentname;
    private String course;
    private int fee;
    public Student() {

    }
    public Student(Long id, String studentname, String course, int fee) {
    
        this.id = id;
        this.studentname = studentname;
        this.course = course;
        this.fee = fee;
    }
    public Long getId() {
        return id;
    }
    public void setId(Long id) {
        this.id = id;
    }
    public String getStudentname() {
        return studentname;
    }
    public void setStudentname(String studentname) {
        this.studentname = studentname;
    }
    public String getCourse() {
        return course;
    }
    public void setCourse(String course) {
        this.course = course;
    }
    public int getFee() {
        return fee;
    }
    public void setFee(int fee) {
        this.fee = fee;
    }

}

Contorller i wrote like this. i stuck with this area how to get the Student names only

 @ModelAttribute("allStudent")
        public List<Student> allUsers() {
            List<Student> userList= service.listAll();
            return userList;
        }

Solution

Here, I'm using <form:select /> , <form:option /> and <form:options /> tags to render HTML dropdown box. And <c:forEach /> for loop each student.

Don't forget to import below taglib to jsp.

<%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c"%>
<%@ taglib uri="http://www.springframework.org/tags/form" prefix="form"%>

For example, POST request path is /students. And modelAttribute="studentForm" will be used to bind Student POJO.

Index.jsp

<form:form modelAttribute="studentForm"
            action="${pageContext.request.contextPath}/students" method="POST">
            <form:select path="studentName">
                <form:option value="NONE" label="Select" />
                <c:forEach var="student" items="${allStudents}">
                    <form:option value="${student.id}" label="${student.studentName}"/>
                </c:forEach>
            </form:select>
</form:form>

By the way, I used camelCase for studentName.

Supposed service.listAll() works fine. When GET request /students is called -

Controller be like

@ModelAttribute(name = "studentForm")
public Student setUp() {
     return new Student();
}

@GetMapping
public String list(Model model) {
    List<Student> students = service.listAll();
    // add to model
   model.addAttribute("allStudent", students);
   // view
   return "index";
}

Method level @ModelAttribute will be invoked before any other method in controller. To use studentForm model attribute in form, we need to initialize first. You can do it without using method level @ModelAttribute.

Answered By - Byaku