Debugging the data in java

 If you want to debug and see all data from array/list in Spring Boot, here are the best ways.

Suppose:

List<Student> students = service.getAllStudent();

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1. Print Using forEach (Best)

students.forEach(System.out::println);

But for this your Student class needs toString().

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2. Add toString() in Entity

In Student.java

@Override
public String toString() {
return "Student [id=" + id +
", firstName=" + firstName +
", lastName=" + lastName +
", email=" + Email + "]";
}

Now console output:

Student [id=1, firstName=Lakhan, lastName=Thakur, email=test@gmail.com]

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3. Traditional Loop

for(Student s : students){

System.out.println(s);

}

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4. Print Specific Values

for(Student s : students){

System.out.println(s.getFirstName());

System.out.println(s.getEmail());
}

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5. Debug in Controller

@GetMapping("/index")
public String getAllStudent(Model model) {

List<Student> students = service.getAllStudent();

students.forEach(System.out::println);

model.addAttribute("students", students);

return "studentPage";
}

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6. See Data in IntelliJ/Eclipse Debugger

Add breakpoint

Click left side line number.

Example:

List<Student> students = service.getAllStudent();

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Run Debug Mode

• Eclipse → Debug As → Spring Boot App
• IntelliJ → Debug button

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Inspect Array/List

Hover mouse on:

students

You can expand all objects.

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7. Convert List to JSON (Very Useful)

System.out.println(new ObjectMapper().writeValueAsString(students));

Import:

import com.fasterxml.jackson.databind.ObjectMapper;

Output:

[
{
"id":1,
"firstName":"Lakhan",
"lastName":"Thakur",
"email":"test@gmail.com"
}
]

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8. Print Size

System.out.println(students.size());

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9. Debug Thymeleaf Data

Inside HTML:

<p th:text="${students}"></p>

or

<p th:text="${studentData.firstName}"></p>

inside th:each.