如何在Java中以通用方式处理null检查？

Question

I have to check null condition for too many methods. how can i do it in generic way rather than repeating the same steps or Is it possible to write?

Here's my code:

<Student>
 <Name></Name>
 <RollNumber></RollNumber>
</Student>

I should throw an exception If user gives null value for Name or RollNumber field. I have already written code below. which is working correctly but i need to write generic method for both scenario and it should work the same as below,

if(student.getName() == null) {
 System.out.println("Name is required to create Student Data");
}

if(student.getRollNumber() == null) {
 System.out.println("RollNumber is required to create Student Data");
}

Note : Name is String and RollNumber is an Integer

Can you please give me an IDEA?

This question may already have an answer here: Avoiding “!= null” statements in Java? 44 answers

My Question is "I don't want avoiding null statement. If user gives null value How Can we throw an exception in generic way?"

Answer 1

If your Student bean always requires non-null values how about constructing the student object with non-null values inside a constructor. As you are doing the validation inside the constructor only no need to the do the same whenever you are using that object

public class Student
{
private String name;
private String rollNumber;

    public Student(String name, String rollNumber)
    {
        setName(name);
        setRollNumber(rollNumber);
    }   

    public String getName()
    {
        return name;
    }

    public String getRollNumber()
    {
        return rollNumber;
    }

    public String setName(String name)
    {
        if(isNull(name))
       {
         throw new NullPointerException("Name is required to create Student Data");
       }
       this.name= name;
    }

    public String setRollNumber(String rollNumber)
    {
        if(isNull(rollNumber))
       {
         throw new NullPointerException("Roll Number is required to create Student Data");
       }
       this.rollNumber = rollNumber 
    }

    private void isNull(String str)
    {
       if(str == null || str.trim().isEmpty())
          return true;
       return false;
    }

}

Answer 2

You should probably take a look at Hibernate Validation . Then you can simply annotate the fields of your bean with @NotNull .

As a bonus you can handle other validations as well.

Answer 3

You can use the Apache Commons String Utils API , which defines operations on String that are null safe.

You can do something like this:-

if (StringUtils.isEmpty(student.getName()) { //this check for both empty String and null and prevents null pointer exceptions

     System.out.println("Name is required to create Student Data");

}

Besides null comparison for just Strings, Assertions are good way to handle nulls you can check here for more info. Make sure to pass -ea argument to JVM as by default it ignores Assertions