What's good practice of creating input validation method in Java?

Question

If I want to validate my input, should I make validation code as private helper methods or create a separate static helper class? Does the validation code increase the size of the object?

More Information

Let's say I have a class

import java.util.Vector;


public class Place {
    private final double    longitude;
    private final double    latitude;
    private final String    id;

    private       String           address;
    private       String           name;
    private       String           types;
    private       String           icon;
    private       String           phoneNumber;
    private       String           websiteUrl;
    private       int              rating;
    private       Vector<Integer>  challenges;

    public static class Builder {
        // required parameter
        private final double    longitude;
        private final double    latitude;
        private final String    id;
        // optional parameter
        private       String           address = "n/a";
        private       String           name = "n/a";
        private       String           icon = "n/a";
        private       String           phoneNumber = "n/a";
        private       String           websiteUrl = "n/a";
        private       String           types = "n/a";
        private       Vector<Integer>  challenges = new Vector<Integer>();
        private       int              rating = 0;

        public Builder(double longitude, double latitude, String id) {
            assert(longitude >= -180.0 && longitude <= 180.0);
            assert(latitude >= -90.0 && longitude <= 90.0);
            this.longitude = longitude;
            this.latitude = latitude;
            this.id = id;
        }

        public Builder address(String address) {
            this.address = address;
            return this;
        }

        public Builder types(String types) {
            this.types = types;
            return this;
        }

        public Builder name(String name) {
            this.name = name;
            return this;
        }

        public Builder icon(String icon) {
            this.icon = icon;
            return this;
        }

        public Builder phoneNumber(String phoneNumber) {
            this.phoneNumber = phoneNumber;
            return this;
        }

        public Builder websiteUrl(String websiteUrl) {
            this.websiteUrl = websiteUrl;
            return this;
        }

        public Builder builder(int rating) {
            this.rating = rating;
            return this;
        }

        public Place build() {
            return new Place(this);
        }
    }

    public Place(Builder builder) {
        // required parameters
        longitude = builder.longitude;
        latitude = builder.latitude;
        id = builder.id;

        // optional parameters
        address = builder.address;
        types = builder.types;
        name = builder.name;
        icon = builder.icon;
        phoneNumber = builder.phoneNumber;
        websiteUrl = builder.websiteUrl;
        rating = builder.rating;
        challenges = builder.challenges;
    }

    public double getLongitude() {
        return longitude;
    }

    public double getLatitude() {
        return latitude;
    }

    public String getId() {
        return id;
    }

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

    public String getAddress() {
        return address;
    }

    public String getTypes() {
        return types;
    }

    public void setTypes(String types) {
        this.types = types;
    }

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

    public String getName() {
        return name;
    }

    public void setIconUrl(String icon) {
        this.icon = icon;
    }

    public String getIcon() {
        return icon;
    }

    public void setPhoneNumber(String phoneNumber) {
        this.phoneNumber = phoneNumber;
    }

    public String getPhoneNumber() {
        return phoneNumber;
    }


    public void setWebsiteUrl(String websiteUrl) {
        this.websiteUrl = websiteUrl;
    }

    public String getWebsiteUrl() {
        return websiteUrl;
    }

    public void setRating(int rating) {
        this.rating = rating;
    }

    public int getRating() {
        return rating;
    }

    @Override
    public String toString() {
        return "(" + Double.toString(longitude) + ", " +  Double.toString(latitude) + ")";
    }

    @Override
    public int hashCode() {
        final int prime = 31;
        int result = 1;
        result = prime * result + ((id == null) ? 0 : id.hashCode());
        return result;
    }

    @Override
    public boolean equals(Object obj) {
        if (this == obj)
            return true;
        if (obj == null)
            return false;
        if (getClass() != obj.getClass())
            return false;
        Place other = (Place) obj;
        if (id == null) {
            if (other.id != null)
                return false;
        }
        else if (!id.equals(other.id))
            return false;
        return true;
    }

    public Vector<Integer> getChallenges() {
        return new Vector<Integer>(challenges);
    }

    public void addChallenges(Integer i) {
        this.challenges.add(i);
    }

    public void showChallenges() {
        for (Integer i : challenges) {
            System.out.print(i + ", ");
        }
    }
}

If I have to validate address argument before setting it, where should I put the code for validating address in this case?

What do you mean by input? method arguments? Provide more context, so folks can address your needs. — Michał Šrajer
– Michał Šrajer, Commented Dec 23, 2011 at 22:59
You probably want to use List<Integer> instead of Vector<Integer>. You are C++ developer aren't you? — Michał Šrajer
– Michał Šrajer, Commented Dec 23, 2011 at 23:15
Yeah, I come from C++ background! Why is List<> better in this case though? Could you elaborate a bit? — roxrook
– roxrook, Commented Dec 23, 2011 at 23:17
It's a longer story, but easy to find on SO or google. In short, a List<> is an interface, and you can pick an optimal implementation like ArrayList, LinkedList or some concurrent list. Vector is synchronized which in most cases makes it unnecessary slower. — Michał Šrajer
– Michał Šrajer, Commented Dec 23, 2011 at 23:30
@MichałŠrajer: Just do a bit Google search, thanks for pointing that out. — roxrook
– roxrook, Commented Dec 23, 2011 at 23:33

Toby Mellor · Accepted Answer · 2017-03-24 12:16:13Z

If you are talking just seeing if the entered String is formatted correctly or if the length is right, then you would use a private method. If you would on the other hand check if the address is correct (look it up on a map) or any more advanced stuff, it would make sense to create a AddressValidator interface and call it from that private method.

The reason for the private method being that you call this both from a constructor, setter or any other method that could suppy an address. The reason for the interface being that you might want to have e.g. an online / offline AddressValidator (MockAddressValidator, or one that calls a different class for each country etc).

As an AddressValidator could be reused in other classes, and to keep your code clean, I would create it as a top level interface + OnlineAddressValidator. This makes your class better readable as well. For full configurability, you might want to think about how you are going to supply the AddressValidator instance, e.g. through the constructor or one defined as a static final validator.

public interface AddressValidator {
    static class AddressValidatorResult {
        // some results, you might want to return some useful feedback (if not valid)

        boolean isValid() {
            throw new IllegalStateException("Method not implemented yet");
        }
    }

    public static class AddressValidationException extends Exception {
        private AddressValidationException(AddressValidatorResult result) {
            // add some implementation
        }
    }


    // don't throw ValidateException here, invalid addresses are normal for
    // validators, even if they aren't for the application that uses them
    AddressValidatorResult validateAddress(String address);
        // don't throw ValidateException here, invalid addresses are normal for
        // validators, even if they aren't for the application that uses them
}

public class DefaultAddressValidator implements AddressValidator {

    public static class Params {
        // some parameters for this specific validator
    }

    private final Params params;

    public DefaultAddressValidator(Params params) {
        // creates this validator
        this.params = params;
    }

    @Override
    public AddressValidatorResult validateAddress(String address) {
        // perform your code here

        // I don't like "return null" as it may lead to bugs
        throw new IllegalStateException("Method not implemented yet");
    }
}


// and use it like this
private void validateAddress(String address) throws AddressValidationException {
    // e.g. field AddressValidator set in constructor 
    AddressValidatorResult result = addressValidator.validateAddress(address);
    if (!result.isValid()) {
        throw new AddressValidationException(result);
    }
}

Community · Accepted Answer · 2020-06-20 09:12:55Z

Should I make validation code as private helper methods or create a separate static helper class?

This totally depends on your context. It's impossible to say what should be the best design, without knowing what you are trying to realise.

After you edit: IMO, it is still not easy to tell you. If you only have to validate the address in one single point of your application (id: the setter method), I would validate it inside the setter method. If the input was invalid, I whould throw an IllegalArgumentException.

Does the validation code increase the size of the object?

However, the answer to your second question is No. To understand why, you have to know what Object Oriented Programming is.

Some references:

aleroot · Accepted Answer · 2011-12-23 23:17:26Z

1

Should I make validation code as private helper methods or create a separate static helper class?

It depends if you think that you'll need to reuse the same method also in another class for the same purpose(input validation) it is better write the method in a separate static helper class so you can reuse the method and maintain it easily. If you write the same private helper method in several class each time that you need to make a changes you have to edit each method in each class, with a static helper class you change the code in one place only ...

answered Dec 23, 2011 at 23:17

aleroot

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1 Comment

roxrook Over a year ago

Nice thought! And I guess it will also be much easier to test my method since I don't have to expose everything as public.

Michał Šrajer · Accepted Answer · 2011-12-23 23:25:22Z

0

Read about PropertyChangeListener and Bean Validation.

answered Dec 23, 2011 at 23:25

Michał Šrajer

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Comments

Jon Story · Accepted Answer · 2011-12-23 23:58:02Z

0

I tend to validate within the get() and set() methods wherever possible - calling external static methods for common tasks such as checking dates or cleaning input (i.e. to avoid sql injection)

If you only use (and are only ever going to use) the validation within one class, keep it as a private helper method. If in doubt, I tend to pull the functionality out into a static helper class. It makes very little difference to the amount of code, is no more effort to implement, and is much more flexible.

answered Dec 23, 2011 at 23:58

Jon Story

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Comments

Arjan Tijms · Accepted Answer · 2013-07-12 10:11:44Z

The short answer is: you should implement your validation code the way that your framework tells you to. Typically, this is a public method or an annotation. An interface could work too. If you add code, your class size will increase.

Data validation should be automatically called by your software's infrastructure. This helps to prevent programmers from forgetting to call the appropriate code. So, the methods should be public (an interface would work too).

Frameworks like Struts, Spring, Hibernate and have their own validation systems. Java EE leverages bean validation.

I recommend bean validation, because it performs validation regardless of the input source. When most people think of input validation, they think of data coming from the user e.g. HTTP Request, command console, Swing text field. Spring and Struts validation is often fine for those situations. But in long lived programs developed for enterprises, other data feeds often get introduced e.g. SQL database updates from another programs, database restoration after a crash, enterprise service bus, JMS.

That is why I prefer bean validation. The downside is that "safe sources" (data that you know is untainted) are validated unnecessarily. But with today's processing power, that should rarely be a significant concern. Java EE Tutorial

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