Dropwizard Forms

Multipart Forms

Multi-part forms are one of the most popular enctype(it specifies how the form should be encoded with submitting) or content types. Each field to be sent in multipart has its content type, name, and data. Boundaries separate all the fields from other fields. Multipart forms are mainly used for uploading files because of their large size.   

The encoding process converts all the spaces to the plus (+) symbol. All non-alphanumerical are converted to hexadecimal values. To send data over the Internet, it follows ASCII characters format. There are two other types of forms: Bound and Unbound. 

Bound forms are those which are linked directly to the table. Any change in the form will be reflected in the table. When you open a bound form it will display the first record of the table. And, any change in this data will be saved in the table directly. 

Unbound forms are not connected to any table. These are blank forms. For example - the login form is an unbound form. When you open these forms no earlier data is visible to you. 

Jersey

Java Jersey helps in creating restful web services in Java. It is an open-source framework that provides support for JAX-RS. JAX-RS provides a set of annotations and interfaces.

JAX-RS only defines while Jersey provides the implementation. And there can be many implementations of a specification. Jersey provides multiple features mentioned below.

• Jersey also provides a servlet that scans pre-defined classes that identify restful resources. 
• It provides support to work with Atom.
• Jersey integrates with Apache HTTP client-server.
• Provide implementation for non-blocking clients.
• Integrate with other java frameworks like Spring, Guice, etc.
• Provide support for declarative servers.
• Ease the development of restful web services.

Adding Bundle

To add a new forms bundle, you must add the following code in the 'initialize' method.

@Override
public void initialize(Bootstrap<Configure> b) {
    b.addBundle(new MultiPartBundle());
}

• The ‘initialize()’ method is a method that initializes a new interface bundle.
   
• The ‘MultiPartBundle()’ class object is passed in the ‘addBundle()’ method. This class extends the object class and implements the bundle interface. The 'object' class is the root of all the classes. And this 'bundle' interface enables the processing of multi-part forms.
   
• The 'addBundle()' method adds the given bundle to the bootstrap. This bootstrap is a pre-start environment for your application. It contains everything required to run the dropwizard command.  

Testing

Add the 'MultiPartFeature' class to 'ResrouseExtension' to test the utilization of multipart forms resources. First, add this class as a provider and then register it on the client using the below code. 

@ExtendWith(DropwizardExtensionsSupport.class)
public class MultiPartTest {
    public static final ResourceExtension re = ResourceExtension.builder()
            .addProvider(MultiPartFeature.class)
            .addResource(new TestResource())
            .build();

    @Test
    public void testClient() {
        final FormDataMultiPart mp = new FormDataMultiPart().field("test-data", "Multipart Form");
        final String response = re.target("/test")
                .register(MultiPartFeature.class)
                .request()
                .post(Entity.entity(mp, mp.getMediaType()), String.class);
        assertThat(response).isEqualTo("Return Multipart Form");
    }

    @Path("test")
    public static class TestResource {
        @POST
        @Consumes(MediaType.MULTIPART_FORM_DATA)
        public String post(@FormDataParam("test-data") String testData) {
            return testData;
        }
    }
}

Explanation:

1. Create a ResourceExtension and name it as 're'.
2. Add the provider using the 'addProvider' method.
3. Add the resource by passing the 'TestResource' object to the 'addResource' method.
4. Call the 'build()' function to start the build process.
5. Create ‘testClient()’ method to add form data.
6. Register the 'MultiPartFeature' class using the above-created method.
7. Compare the test result with the string 'Return Multipart Form.' And return the result accordingly.
8. Finally, create a 'TestResource' class and return test data.
    

This was all about Dropwizard Forms. Let's now discuss some of the frequently asked questions related to our topic. 

Frequently Asked Questions

What is Dropwizard? 

Dropwizard is an open-source framework of Java. It is used for the fast development of high-performance RESTful web services. 

What are the two different types of forms?

Forms are of two types - bound and unbound. The bound forms are directly connected to the data source. Alternatively, the unbound forms do not direct link to the data source. 

What are Multipart-forms data?

Multi-part forms are one of the most used enctype/content type. In multipart, each of the fields to be sent has its content type, file name, and data separated by boundary from other fields.

What is Jersey?

Jersey is an open-source framework that supports JAX-RS. It provides a set of annotations and interfaces that helps in creating restful web services. 

What is bootstrap in Dropwizard?

The bootstrap is a pre-start (temporary) application environment. It contains all of the components needed to bootstrap a Dropwizard command.

Conclusion 

This article contains basic information about the Dropwizard Forms module. In this article, we have discussed how to add and test forms. Along with that, we did the discussion of what multipart forms are and how to work on them via Jersey. The reader can carry out a thorough understanding of the topic by referring to the Official Documentation. For more information, Refer-

• Dropwizard JDBI3
• Dropwizard Migrations
• Dropwizard Example
   

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