Validating HTTP data with Play

Validations ensure that the data has certain values or meets specific requirements. You can use validation to verify that your models are correct before saving them to the database, or use them directly on HTTP parameters to validate a simple form.

How validation works in Play

Each request has it own Validation object which collects errors. There are three ways to define validations.

1. In a controller method, call methods on the controller’s validation field directly. You can also access a subset of the API using the play.data.validation.Validation class’ static methods.
2. Add validation annotations to the controller method’s parameter declarations.
3. Add the @Valid annotation to action methods’ POJO parameters, and add validation annotations to the POJO properties.

The validation object maintains a collection of play.data.validation.Error objects. Each error has two properties:

• The key. This helps you to determine which data element caused the error. The key value can be set arbitrarily but when Play generates errors, it uses default conventions that follow the Java variables’ names.

• The message. This contains the error’s textual description. The message can be a plain message or refer to a key from a message bundle (typically for internationalization support).

Using the first approach, let’s see how to validate a simple HTTP parameter:

public static void hello(String name) {
     validation.required(name);
     …
}

This code checks that the name variable is correctly set. If not, the corresponding error is added to the current errors collection.

You can repeat this operation for each validation you need:

public static void hello(String name, Integer age) {
     validation.required(name);
     validation.required(age);
     validation.min(age, 0);
     …
}

Validation error messages

At the end of the validation you can check if any errors have been created and display them:

public static void hello(String name, Integer age) {
     validation.required(name);
     validation.required(age);
     validation.min(age, 0);

     if(validation.hasErrors()) {
         for(Error error : validation.errors()) {
             System.out.println(error.message());
         }
     }
}

Assuming that name and age are null, this would display:

Required
Required

This is because the default message, defined in $PLAY_HOME/resources/messages, is:

validation.required=Required

There are three ways to customise the validation message.

1. Override the default message, by redefining the message in your application’s messages file.
2. Provide a custom message as an additional validation parameter.
3. Provide a message key for a localised message as an additional validation parameter.

Localised validation messages

The simplest way to override these messages is to use the same message key for a message in your application’s conf/messages file. For example:

validation.required = Please enter a value

You can also provide localisations in other languages, as described in Internationalization.

Validation message parameters

You can use a placeholder in the message for the error key:

validation.required=%s is required

This changes the output to:

name is required
age is required

This error key defaults to the parameter name, and is itself used to look up a message. For example, the name parameter in the hello action method above could be localised with:

name = Customer name

This would result in the output:

Customer name is required
age is required

You can change also override the error key using the error.message(String key) method. For example:

Error error = validation.required(name).error;
if(error != null) {
    System.out.println(error.message("Customer name"));
}

Several of the built-in validations define additional message parameters that correspond to the validation parameters. For example, the ‘match’ validation defines a second String parameter for the specified regular expression, which differs from the %s placeholder above in that it specifies the parameter index ‘2’:

validation.match=Must match %2$s

Similarly, the ‘range’ validation defines two additional numeric parameters, with indices 2 and 3:

validation.range=Not in the range %2$d through %3$d

Look in the file $PLAY_HOME/resources/messages to see which other validations have parameters.

Custom localised validation messages

The validation messages in $PLAY_HOME/resources/messages use the default message key for each of Play’s built-in validations. You can specify a different message key. For example:

validation.required.em = You must enter the %s!

Use this new message key for the message, for manual validation in the action method:

validation.required(manualKey).message("validation.required.em");

Alternatively, use the key in the annotation’s message parameter:

public static void hello(@Required(message="validation.required.em") String name) {
   …
}

You can use the same technique with validation annotations on JavaBean properties:

public static void hello(@Valid Person person) {
   …
} 

public class Person extends Model {
   @Required(message = "validation.required.emphasis")
   public String name;
   …
}

Custom literal (non-localised) validation messages

The Play message look-up just returns the message key if there is no message defined for the key, which means you can also just use a literal message instead of the message key if you prefer. Using the same examples as above, for manual validation:

validation.required(manualKey).message("Give us a name!");

For action method parameter annotations:

public static void save(@Required(message = "Give us a name!") String name) {
   …
}

For JavaBean property annotations:

public static void save(@Valid Person person) {
   …
}

public class Person extends Model {
   @Required(message = "Give us a name!")
   public String name;
   …
}

Displaying validation errors in the template

In most cases you want to display the error messages in the view template. You can access them in the template using the errors object. Some tags help you to display the errors:

Let’s see a sample:

public static void hello(String name, Integer age) {
   validation.required(name);
   validation.required(age);
   validation.min(age, 0);
   render(name, age);
}

and now the template:

#{ifErrors}

   <h1>Oops…</h1>

   #{errors}
       <li>${error}</li>
   #{/errors}

#{/ifErrors}
#{else}

   Hello ${name}, you are ${age}.

#{/else}

But in a real application you want to redisplay the original form. So you will have two actions: one to display the form and another one to handle the POST.

Of course the validation will occur in the second action and if some error occurs you will have to redirect to the first action. In this case you need a special trick to keep your errors during the redirect. Use the validation.keep() method. This will save the errors collection for the next action.

Let’s see a real sample:

public class Application extends Controller {

   public static void index() {
      render();
   }

   public static void hello(String name, Integer age) {
      validation.required(name);
      validation.required(age);
      validation.min(age, 0);
      if(validation.hasErrors()) {
          params.flash(); // add http parameters to the flash scope
          validation.keep(); // keep the errors for the next request
          index();
      }
      render(name, age);
   }

}

And the view/Application/index.html template:

#{ifErrors}
   <h1>Oops…</h1>

   #{errors}
       <li>${error}</li>
   #{/errors}
#{/ifErrors}

#{form @Application.hello()}
   <div>
      Name: <input type="text" name="name" value="${flash.name}" />
   </div>
   <div>
      Age: <input type="text" name="age" value="${flash.age}" />
   </div>
   <div>
      <input type="submit" value="Say hello" />
   </div>
#{/form}

You can create a better user experience by displaying each error message next to the field that generated the error:

#{ifErrors}
   <h1>Oops…</h1>
#{/ifErrors}

#{form @Application.hello()}
   <div>
      Name: <input type="text" name="name" value="${flash.name}" />
      <span class="error">#{error 'name' /}</span>
   </div>
   <div>
      Age: <input type="text" name="age" value="${flash.age}" />
      <span class="error">#{error 'age' /}</span>
   </div>
   <div>
      <input type="submit" value="Say hello" />
   </div>
#{/form}

Validation annotations

The annotations in the play.data.validation package provide an alternative and more concise way to specify validation constraints, with an annotation that corresponds to each Validation object method. To use the validation annotations, just annotate the controller method parameters:

public static void hello(@Required String name, @Required @Min(0) Integer age) {
   if(validation.hasErrors()) {
       params.flash(); // add http parameters to the flash scope
       validation.keep(); // keep the errors for the next request
       index();
   }
   render(name, age);
}

Validating complex objects

You can also use the validation annotations to easily add constraints to your model object’s properties, and then in the controller specify that all properties must be valid. Let’s rewrite the previous example using a User class.

First the User class, with validation annotations on the properties:

package models;

public class User {

    @Required
    public String name;

    @Required
    @Min(0)
    public Integer age;
}

Then the modified hello action, which uses the @Valid annotation to specify that all of the Userobject’s properties must be valid:

public static void hello(@Valid User user) {
   if(validation.hasErrors()) {
       params.flash(); // add http parameters to the flash scope
       validation.keep(); // keep the errors for the next request
       index();
   }
   render(name, age);
}

And finally the modified form:

#{ifErrors}
   <h1>Oops…</h1>
#{/ifErrors}

#{form @Application.hello()}
   <div>
      Name: <input type="text" name="user.name" value="${flash['user.name']}" />
      <span class="error">#{error 'user.name' /}</span>
   </div>
   <div>
      Age: <input type="text" name="user.age" value="${flash['user.age']}" />
      <span class="error">#{error 'user.age' /}</span>
   </div>
   <div>
      <input type="submit" value="Say hello" />
   </div>
#{/form}

Built-in validations

The play.data.validation package contains several built-in validations that you can use on theValidation object or with annotations.

Custom validation

Can’t find the validator you need in the play.data.validation package? Write your own. You can use the generic @CheckWith annotation to bind your own Check implementation.

For example:

public class User {

    @Required
    @CheckWith(MyPasswordCheck.class)
    public String password;

    static class MyPasswordCheck extends Check {

        public boolean isSatisfied(Object user, Object password) {
            return notMatchPreviousPasswords(password);
        }

    }
}

Continuing the discussion

The last layer of a Play application: Domain object model.