java.lang.StackOverflowError occurs when I try add another product to customer

Question

Welcome, I'am using a SPRING MVC, SPRING DATA, HIBERNATE, Maven

As in title. When I added first product, everything was okay but the problem occurs when I would like to add next product to customer.

My Entities

@Entity
@Table(name="customer")
public class Customer {

    @Id
    @GeneratedValue(strategy=GenerationType.IDENTITY)
    @Column(name="customer_id")
    private int id;

    @Column(name="name")
    private String name;

    @Column(name="email")
    private String email;

    @Column(name="address")
    private String address;

    @OneToOne(cascade=CascadeType.ALL)
    private CustomerDetails customerDetails;

    @ManyToMany(mappedBy="customers",cascade=CascadeType.ALL, fetch=FetchType.EAGER)
    private List<Products>products;

    public Customer() {
    }

    public Customer(CustomerDetails customerDetails)
    {
        this.customerDetails=customerDetails;
    }

    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getEmail() {
        return email;
    }

    public void setEmail(String email) {
        this.email = email;
    }

    public String getAddress() {
        return address;
    }

    public void setAddress(String address) {
        this.address = address;
    }



    public CustomerDetails getCustomerDetails() {
        return customerDetails;
    }

    public void setCustomerDetails(CustomerDetails customerDetails) {
        this.customerDetails = customerDetails;
    }




    public void addCustomerDetails(CustomerDetails cd)
    {
        cd.setCustomer(this);
    }


    @Override
    public String toString() {
        return "Customer [id=" + id + ", name=" + name + ", email=" + email + ", address=" + address
                + ", customerDetails=" + customerDetails + "]";
    }



    //new added
    public List<Products> getProducts() {
        return products;
    }

    public void setProducts(List<Products> products) {
        this.products = products;
    }


    public void addProduct(Products product)
    {
        if(products==null)
        {
            products=new ArrayList<>();
        }   
        products.add(product);
        product.addCustomer(this);
    }

}

@Entity
@Table(name="Produkty")
public class Products {

    @Id
    @GeneratedValue(strategy=GenerationType.IDENTITY)
    @Column
    private int id;

    @Column
    private String name;

    @Column
    private String type;

    @Column
    private String expiryDate;


    @ManyToMany(cascade= {CascadeType.DETACH,CascadeType.MERGE,CascadeType.PERSIST,CascadeType.REFRESH}, fetch=FetchType.EAGER)
    private List<Customer> customers;


    public int getId() {
        return id;
    }


    public void setId(int id) {
        this.id = id;
    }


    public String getName() {
        return name;
    }


    public void setName(String name) {
        this.name = name;
    }


    public String getType() {
        return type;
    }


    public void setType(String type) {
        this.type = type;
    }


    public String getExpiryDate() {
        return expiryDate;
    }


    public void setExpiryDate(String expiryDate) {
        this.expiryDate = expiryDate;
    }


    public List<Customer> getCustomers() {
        return customers;
    }


    public void setCustomers(List<Customer> customers) {
        this.customers = customers;
    }


    @Override
    public String toString() {
        return "Products [id=" + id + ", name=" + name + ", type=" + type + ", expiryDate=" + expiryDate
                + ", customers=" + customers + "]";
    }

    public void addCustomer(Customer customer)
    {
        if(customers==null)
        {
            customers=new ArrayList<>();
        }
        customers.add(customer);
    }
}

MyControllers:

@Controller
@RequestMapping("/customer")
public class CustomerController {

    @Autowired
    private CustomerService service;



    @GetMapping("/home")
public String home(Model model)
    {       
        List<Customer>customers=service.getCustomers();
        model.addAttribute("message","Hello from Spring MVC");model.addAttribute("customers",customers);
        return "home-page";
    }

    @GetMapping("/showForm")
    public String showForm(Map<String,Object>model)
    {
        Customer customer=new Customer();

        model.put("customer",customer);
        return "new-customer";
    }

    @PostMapping("/add")
    public String addCustomer(@ModelAttribute("customer") Customer customer)
    {
        CustomerDetails cd=new CustomerDetails();
        customer.setCustomerDetails(cd);
        cd.setCustomer(customer);

        service.saveCustomer(customer);
        return "redirect:/customer/home";
    }

    /*
    @RequestMapping("/showCustomerDetailsForm")
    public String showCustomerDetailsForm(@RequestParam int id ,Model model)
    {
        Customer customer=service.getCustomer(id);
        model.addAttribute("customer",customer);
        return "details-form";
    }

    @RequestMapping("/addDetails")
    public String addCustomerDetails(@ModelAttribute("customerDetails") CustomerDetails customerDt)
    {
        serviceCD.saveCustomer(customerDt);
        return "redirect:/customer/home";
    }
    */


    @GetMapping("/edit")
    public String editCustomer(@RequestParam int id, Model model)
    {
        Customer customer=service.getCustomer(id);
        model.addAttribute("customer",customer);
        return "edit-customer";
    }


    @GetMapping("/delete")
    public String deleteCustomer(@RequestParam int id)
    {
        service.deleteCustomer(id);
        return "redirect:/customer/home";
    }

    @GetMapping("/search")
    public String search(@RequestParam String keyword,Model model)
    {
        List<Customer>customers=service.search(keyword);
        model.addAttribute("customers",customers);
        return "search-page";
    }
}  

@Controller
@RequestMapping("/customer/product")
public class ProductController {

    @Autowired
    private CustomerService service;

    @RequestMapping("/showForm")
    public String showProductsForm(@RequestParam int id,Model model)
    {
        Customer customer=service.getCustomer(id);
        Products product=new Products();
        model.addAttribute("customer",customer);
        model.addAttribute("product",product);
        return "product-form";
    }

    @RequestMapping("/add")
    public String addProductToCustomer(@RequestParam int id, @ModelAttribute("product")Products product)
    {
        Customer customer=service.getCustomer(id);
        customer.addProduct(product);
        service.saveCustomer(customer);

        return "redirect:/customer/home";   
    }

}

Body of my product-form JSP:

<body>

<div align="center">
<table>
<form:form action="add?id=${customer.id}" modelAttribute="product">

<tr>
<td>${customer.id}</td>
</tr>

<tr>
<td>Name:</td>
<td><form:input path="name"/>
</td>
</tr>

<tr>
<td>Type:</td>
<td><form:input path="type"/>
</td>
</tr>

<tr>
<td>Expiry date:</td>
<td><form:input path="expiryDate"/>
</td>
</tr>

<tr>
<td><input type="submit" value="Submit" /></td>
</tr>

</form:form>
</table>
</div>


</body>

body of my home-page.jsp

    <div align="center">

        <h1>Customer Manager</h1>
        <form method="get" action="search">
            <input type="text" name="keyword" />
             <input type="submit" value="Search" />
        </form>

        <h3> <a href="showForm">new customer</a></h3>


        <table border="1" padding="5">
            <tr>
                <th>ID</th>
                <th>Name</th>
                <th>E-mail</th>
                <th>Address</th>
                <th>Action</th>


            </tr>
            <c:forEach items="${customers}" var="customer">
            <tr>
                <td>${customer.id}</td>
                <td>${customer.name}</td>
                <td>${customer.email}</td>
                <td>${customer.address}</td>
                <td><a href ="edit?id=${customer.id}">Edit</a> <a href ="delete?id=${customer.id}">Delete</a></td>
                <td> <a href="product/showForm?id=${customer.id}" >Add product</a>
            </tr>
            </c:forEach>
        </table>

Stacktrace:

gru 16, 2019 10:22:47 AM org.apache.catalina.core.StandardWrapperValve invoke
SEVERE: Servlet.service() for servlet [dispatcher] in context with path [/spring_hib_config_web] threw exception [Handler dispatch failed; nested exception is java.lang.StackOverflowError] with root cause
java.lang.StackOverflowError
    at java.lang.AbstractStringBuilder.append(Unknown Source)
    at java.lang.StringBuilder.append(Unknown Source)
    at java.lang.StringBuilder.<init>(Unknown Source)
    at com.firstapp.entity.CustomerDetails.toString(CustomerDetails.java:78)
    at java.lang.String.valueOf(Unknown Source)
    at java.lang.StringBuilder.append(Unknown Source)
    at com.firstapp.entity.Customer.toString(Customer.java:104)
    at java.lang.String.valueOf(Unknown Source)
    at java.lang.StringBuilder.append(Unknown Source)
    at com.firstapp.entity.CustomerDetails.toString(CustomerDetails.java:78)
    at java.lang.String.valueOf(Unknown Source)
    at java.lang.StringBuilder.append(Unknown Source)
    at com.firstapp.entity.Customer.toString(Customer.java:104)
    at java.lang.String.valueOf(Unknown Source)
    at java.lang.StringBuilder.append(Unknown Source)
    at com.firstapp.entity.CustomerDetails.toString(CustomerDetails.java:78)
    at java.lang.String.valueOf(Unknown Source)
    at java.lang.StringBuilder.append(Unknown Source)
    at com.firstapp.entity.Customer.toString(Customer.java:104)
    at java.lang.String.valueOf(Unknown Source)
    at java.lang.StringBuilder.append(Unknown Source)
    at com.firstapp.entity.CustomerDetails.toString(CustomerDetails.java:78)
    at java.lang.String.valueOf(Unknown Source)
    at java.lang.StringBuilder.append(Unknown Source)
    at com.firstapp.entity.Customer.toString(Customer.java:104)
    at java.lang.String.valueOf(Unknown Source)
    at java.lang.StringBuilder.append(Unknown Source)
    at com.firstapp.entity.CustomerDetails.toString(CustomerDetails.java:78)
    at java.lang.String.valueOf(Unknown Source)
    at java.lang.StringBuilder.append(Unknown Source)
    at com.firstapp.entity.Customer.toString(Customer.java:104)
    at java.lang.String.valueOf(Unknown Source)
    at java.lang.StringBuilder.append(Unknown Source)
    at com.firstapp.entity.CustomerDetails.toString(CustomerDetails.java:78)
    at java.lang.String.valueOf(Unknown Source)
    at java.lang.StringBuilder.append(Unknown Source)
    at com.firstapp.entity.Customer.toString(Customer.java:104)
    at java.lang.String.valueOf(Unknown Source)
    at java.lang.StringBuilder.append(Unknown Source)
    at com.firstapp.entity.CustomerDetails.toString(CustomerDetails.java:78)
    at java.lang.String.valueOf(Unknown Source)
    at java.lang.StringBuilder.append(Unknown Source)
    at com.firstapp.entity.Customer.toString(Customer.java:104)
    at java.lang.String.valueOf(Unknown Source)
    at java.lang.StringBuilder.append(Unknown Source)
    at com.firstapp.entity.CustomerDetails.toString(CustomerDetails.java:78)
    at java.lang.String.valueOf(Unknown Source)
    at java.lang.StringBuilder.append(Unknown Source)
    at com.firstapp.entity.Customer.toString(Customer.java:104)
    at java.lang.String.valueOf(Unknown Source)
    at java.lang.StringBuilder.append(Unknown Source)
    at com.firstapp.entity.CustomerDetails.toString(CustomerDetails.java:78)
    at java.lang.String.valueOf(Unknown Source)
    at java.lang.StringBuilder.append(Unknown Source)
    at com.firstapp.entity.Customer.toString(Customer.java:104)
    at java.lang.String.valueOf(Unknown Source)
    at java.lang.StringBuilder.append(Unknown Source)
    at com.firstapp.entity.CustomerDetails.toString(CustomerDetails.java:78)
    at java.lang.String.valueOf(Unknown Source)
    at java.lang.StringBuilder.append(Unknown Source)
    at com.firstapp.entity.Customer.toString(Customer.java:104)
    at java.lang.String.valueOf(Unknown Source)
    at java.lang.StringBuilder.append(Unknown Source)
    at com.firstapp.entity.CustomerDetails.toString(CustomerDetails.java:78)
    at java.lang.String.valueOf(Unknown Source)
    at java.lang.StringBuilder.append(Unknown Source)
    at com.firstapp.entity.Customer.toString(Customer.java:104)
    at java.lang.String.valueOf(Unknown Source)
    at java.lang.StringBuilder.append(Unknown Source)
    at com.firstapp.entity.CustomerDetails.toString(CustomerDetails.java:78)
    at java.lang.String.valueOf(Unknown Source)
    at java.lang.StringBuilder.append(Unknown Source)
    at com.firstapp.entity.Customer.toString(Customer.java:104)
    at java.lang.String.valueOf(Unknown Source)
    at java.lang.StringBuilder.append(Unknown Source)
    at com.firstapp.entity.CustomerDetails.toString(CustomerDetails.java:78)
    at java.lang.String.valueOf(Unknown Source)
    at java.lang.StringBuilder.append(Unknown Source)
    at com.firstapp.entity.Customer.toString(Customer.java:104)
    at java.lang.String.valueOf(Unknown Source)
    at java.lang.StringBuilder.append(Unknown Source)
    at com.firstapp.entity.CustomerDetails.toString(CustomerDetails.java:78)
    at java.lang.String.valueOf(Unknown Source)
    at java.lang.StringBuilder.append(Unknown Source)
    at com.firstapp.entity.Customer.toString(Customer.java:104)
    at java.lang.String.valueOf(Unknown Source)
    at java.lang.StringBuilder.append(Unknown Source)
    at com.firstapp.entity.CustomerDetails.toString(CustomerDetails.java:78)
    at java.lang.String.valueOf(Unknown Source)
    at java.lang.StringBuilder.append(Unknown Source)
    at com.firstapp.entity.Customer.toString(Customer.java:104)
    at java.lang.String.valueOf(Unknown Source)
    at java.lang.StringBuilder.append(Unknown Source)
    at com.firstapp.entity.CustomerDetails.toString(CustomerDetails.java:78)
    at java.lang.String.valueOf(Unknown Source)
    at java.lang.StringBuilder.append(Unknown Source)
    at com.firstapp.entity.Customer.toString(Customer.java:104)
    at java.lang.String.valueOf(Unknown Source)
    at java.lang.StringBuilder.append(Unknown Source)
    at com.firstapp.entity.CustomerDetails.toString(CustomerDetails.java:78)
    at java.lang.String.valueOf(Unknown Source)
    at java.lang.StringBuilder.append(Unknown Source)
    at com.firstapp.entity.Customer.toString(Customer.java:104)
    at java.lang.String.valueOf(Unknown Source)
    at java.lang.StringBuilder.append(Unknown Source)
    at com.firstapp.entity.CustomerDetails.toString(CustomerDetails.java:78)
    at java.lang.String.valueOf(Unknown Source)
    at java.lang.StringBuilder.append(Unknown Source)
    at com.firstapp.entity.Customer.toString(Customer.java:104)
    at java.lang.String.valueOf(Unknown Source)
    at java.lang.StringBuilder.append(Unknown Source)
    at com.firstapp.entity.CustomerDetails.toString(CustomerDetails.java:78)
    at java.lang.String.valueOf(Unknown Source)
    at java.lang.StringBuilder.append(Unknown Source)
    at com.firstapp.entity.Customer.toString(Customer.java:104)
    at java.lang.String.valueOf(Unknown Source)
    at java.lang.StringBuilder.append(Unknown Source)
    at com.firstapp.entity.CustomerDetails.toString(CustomerDetails.java:78)
    at java.lang.String.valueOf(Unknown Source)
    at java.lang.StringBuilder.append(Unknown Source)
    at com.firstapp.entity.Customer.toString(Customer.java:104)
    at java.lang.String.valueOf(Unknown Source)
    at java.lang.StringBuilder.append(Unknown Source)
    at com.firstapp.entity.CustomerDetails.toString(CustomerDetails.java:78)
    at java.lang.String.valueOf(Unknown Source)
    at java.lang.StringBuilder.append(Unknown Source)
    at com.firstapp.entity.Customer.toString(Customer.java:104)
    at java.lang.String.valueOf(Unknown Source)
    at java.lang.StringBuilder.append(Unknown Source)
    at com.firstapp.entity.CustomerDetails.toString(CustomerDetails.java:78)
    at java.lang.String.valueOf(Unknown Source)
    at java.lang.StringBuilder.append(Unknown Source)
    at com.firstapp.entity.Customer.toString(Customer.java:104)
    at java.lang.String.valueOf(Unknown Source)
    at java.lang.StringBuilder.append(Unknown Source)
    at com.firstapp.entity.CustomerDetails.toString(CustomerDetails.java:78)
    at java.lang.String.valueOf(Unknown Source)
    at java.lang.StringBuilder.append(Unknown Source)
    at com.firstapp.entity.Customer.toString(Customer.java:104)
    at java.lang.String.valueOf(Unknown Source)
    at java.lang.StringBuilder.append(Unknown Source)
    at com.firstapp.entity.CustomerDetails.toString(CustomerDetails.java:78)
    at java.lang.String.valueOf(Unknown Source)
    at java.lang.StringBuilder.append(Unknown Source)
    at com.firstapp.entity.Customer.toString(Customer.java:104)
    at java.lang.String.valueOf(Unknown Source)
    at java.lang.StringBuilder.append(Unknown Source)
    at com.firstapp.entity.CustomerDetails.toString(CustomerDetails.java:78)
    at java.lang.String.valueOf(Unknown Source)
    at java.lang.StringBuilder.append(Unknown Source)
    at com.firstapp.entity.Customer.toString(Customer.java:104)
    at java.lang.String.valueOf(Unknown Source)
    at java.lang.StringBuilder.append(Unknown Source)
    at com.firstapp.entity.CustomerDetails.toString(CustomerDetails.java:78)
    at java.lang.String.valueOf(Unknown Source)
    at java.lang.StringBuilder.append(Unknown Source)
    at com.firstapp.entity.Customer.toString(Customer.java:104)
    at java.lang.String.valueOf(Unknown Source)
    at java.lang.StringBuilder.append(Unknown Source)
    at com.firstapp.entity.CustomerDetails.toString(CustomerDetails.java:78)
    at java.lang.String.valueOf(Unknown Source)
    at java.lang.StringBuilder.append(Unknown Source)
    at com.firstapp.entity.Customer.toString(Customer.java:104)
    at java.lang.String.valueOf(Unknown Source)
    at java.lang.StringBuilder.append(Unknown Source)
    at com.firstapp.entity.CustomerDetails.toString(CustomerDetails.java:78)
    at java.lang.String.valueOf(Unknown Source)
    at java.lang.StringBuilder.append(Unknown Source)
    at com.firstapp.entity.Customer.toString(Customer.java:104)
    at java.lang.String.valueOf(Unknown Source)
    at java.lang.StringBuilder.append(Unknown Source)
    at com.firstapp.entity.CustomerDetails.toString(CustomerDetails.java:78)
    at java.lang.String.valueOf(Unknown Source)
    at java.lang.StringBuilder.append(Unknown Source)
    at com.firstapp.entity.Customer.toString(Customer.java:104)
    at java.lang.String.valueOf(Unknown Source)
    at java.lang.StringBuilder.append(Unknown Source)
    at com.firstapp.entity.CustomerDetails.toString(CustomerDetails.java:78)
    at java.lang.String.valueOf(Unknown Source)
    at java.lang.StringBuilder.append(Unknown Source)
    at com.firstapp.entity.Customer.toString(Customer.java:104)
    at java.lang.String.valueOf(Unknown Source)
    at java.lang.StringBuilder.append(Unknown Source)
    at com.firstapp.entity.CustomerDetails.toString(CustomerDetails.java:78)
    at java.lang.String.valueOf(Unknown Source)
    at java.lang.StringBuilder.append(Unknown Source)
    at com.firstapp.entity.Customer.toString(Customer.java:104)
    at java.lang.String.valueOf(Unknown Source)
    at java.lang.StringBuilder.append(Unknown Source)
    at com.firstapp.entity.CustomerDetails.toString(CustomerDetails.java:78)
    at java.lang.String.valueOf(Unknown Source)
    at java.lang.StringBuilder.append(Unknown Source)
    at com.firstapp.entity.Customer.toString(Customer.java:104)
    at java.lang.String.valueOf(Unknown Source)
    at java.lang.StringBuilder.append(Unknown Source)
    at com.firstapp.entity.CustomerDetails.toString(CustomerDetails.java:78)
    at java.lang.String.valueOf(Unknown Source)
    at java.lang.StringBuilder.append(Unknown Source)
    at com.firstapp.entity.Customer.toString(Customer.java:104)
    at java.lang.String.valueOf(Unknown Source)
    at java.lang.StringBuilder.append(Unknown Source)
    at com.firstapp.entity.CustomerDetails.toString(CustomerDetails.java:78)
    at java.lang.String.valueOf(Unknown Source)
    at java.lang.StringBuilder.append(Unknown Source)
    at com.firstapp.entity.Customer.toString(Customer.java:104)
    at java.lang.String.valueOf(Unknown Source)
    at java.lang.StringBuilder.append(Unknown Source)
    at com.firstapp.entity.CustomerDetails.toString(CustomerDetails.java:78)
    at java.lang.String.valueOf(Unknown Source)
    at java.lang.StringBuilder.append(Unknown Source)
    at com.firstapp.entity.Customer.toString(Customer.java:104)
    at java.lang.String.valueOf(Unknown Source)
    at java.lang.StringBuilder.append(Unknown Source)
    at com.firstapp.entity.CustomerDetails.toString(CustomerDetails.java:78)
    at java.lang.String.valueOf(Unknown Source)
    at java.lang.StringBuilder.append(Unknown Source)
    at com.firstapp.entity.Customer.toString(Customer.java:104)
    at java.lang.String.valueOf(Unknown Source)
    at java.lang.StringBuilder.append(Unknown Source)
    at com.firstapp.entity.CustomerDetails.toString(CustomerDetails.java:78)
    at java.lang.String.valueOf(Unknown Source)
    at java.lang.StringBuilder.append(Unknown Source)
    at com.firstapp.entity.Customer.toString(Customer.java:104)
    at java.lang.String.valueOf(Unknown Source)
    at java.lang.StringBuilder.append(Unknown Source)
    at com.firstapp.entity.CustomerDetails.toString(CustomerDetails.java:78)
    at java.lang.String.valueOf(Unknown Source)
    at java.lang.StringBuilder.append(Unknown Source)
    at com.firstapp.entity.Customer.toString(Customer.java:104)
    at java.lang.String.valueOf(Unknown Source)
    at java.lang.StringBuilder.append(Unknown Source)
    at com.firstapp.entity.CustomerDetails.toString(CustomerDetails.java:78)
    at java.lang.String.valueOf(Unknown Source)
    at java.lang.StringBuilder.append(Unknown Source)
    at com.firstapp.entity.Customer.toString(Customer.java:104)
    at java.lang.String.valueOf(Unknown Source)
    at java.lang.StringBuilder.append(Unknown Source)
    at com.firstapp.entity.CustomerDetails.toString(CustomerDetails.java:78)
    at java.lang.String.valueOf(Unknown Source)
    at java.lang.StringBuilder.append(Unknown Source)
    at com.firstapp.entity.Customer.toString(Customer.java:104)
    at java.lang.String.valueOf(Unknown Source)
    at java.lang.StringBuilder.append(Unknown Source)
    at com.firstapp.entity.CustomerDetails.toString(CustomerDetails.java:78)
    at java.lang.String.valueOf(Unknown Source)
    at java.lang.StringBuilder.append(Unknown Source)
    at com.firstapp.entity.Customer.toString(Customer.java:104)
    at java.lang.String.valueOf(Unknown Source)
    at java.lang.StringBuilder.append(Unknown Source)
    at com.firstapp.entity.CustomerDetails.toString(CustomerDetails.java:78)
    at java.lang.String.valueOf(Unknown Source)
    at java.lang.StringBuilder.append(Unknown Source)
    at com.firstapp.entity.Customer.toString(Customer.java:104)
    at java.lang.String.valueOf(Unknown Source)
    at java.lang.StringBuilder.append(Unknown Source)
    at com.firstapp.entity.CustomerDetails.toString(CustomerDetails.java:78)
    at java.lang.String.valueOf(Unknown Source)
    at java.lang.StringBuilder.append(Unknown Source)
    at com.firstapp.entity.Customer.toString(Customer.java:104)
    at java.lang.String.valueOf(Unknown Source)
    at java.lang.StringBuilder.append(Unknown Source)
    at com.firstapp.entity.CustomerDetails.toString(CustomerDetails.java:78)
    at java.lang.String.valueOf(Unknown Source)
    at java.lang.StringBuilder.append(Unknown Source)
    at com.firstapp.entity.Customer.toString(Customer.java:104)
    at java.lang.String.valueOf(Unknown Source)
    at java.lang.StringBuilder.append(Unknown Source)
    at com.firstapp.entity.CustomerDetails.toString(CustomerDetails.java:78)

Anyone has any idea? I will be grateful. Thanks

Answer 1

As you can see in the StackTrace the to Customer and CustomerDetails toString methods are causing the StackoverflowError.

You have to take care with bi-directional references and make sure that calling toString on one side will not result in a circular call.