In the last posts we saw how to access query, path and form parameters in MVC Controllers. This post shows how multiple parameters can be mapped to an object using the @BeanParam annotation.

Let’s reuse the simple HTML form from the post about form parameters:

<form action="submit" method="post">
  <label>ID:</label>
  <input type="text" name="id" />

  <label>Name:</label>
  <input type="text" name="name" />

  <label>Role:</label>
  <select name="role">
	<option value="admin">Admin</option>
	<option value="reporter">Reporter</option>
	<option value="accountant">Accountant</option>
  </select>

  <input type="submit"/>
</form>

This defines a simple form containing two text input fields and a select menu with three options.

In the previous post about form parameters, we learned that we can access these parameters by annotating controller parameters with @FormParam.

However, this approach is cumbersome if the form has more than a few parameters. In these situations we typically want to map form parameters to a separate object. @BeanParams helps us with doing exactly this.

With @BeanParam we can write:

@POST
@Path("submit")
@Controller
public String submit(@BeanParam User user) {
 // use user ..
}

The User class looks like this:

public class User {

 @FormParam("id")
 private long id;

 @FormParam("name")
 private String name;

 @FormParam("role")
 private Role role;
 
 // getters and setters
}

When the controller method is called a new instance of User will automatically be created. The fields of the created object will be filled with the passed form parameters.

@BeanParam and other parameter annotations

Classes used with @BeanParam are not limited to form parameters. All parameter annotations shown in previous blog posts (@QueryParam, @PathParam, etc.) can be used inside bean parameters.

For example:

@GET
@Path("/date/{year}/{month}")
public String get(@BeanParam RequestData data) {
 ...
}

public class RequestData {

 @PathParam("year")
 private int year;

 @PathParam("month")
 private int month;

 @QueryParam("name")
 private String name;

 // getters and setters
}

If we now send a HTTP GET request to

/date/2016/02?name=john

the values 2016, 2 and john will be injected to the fields year, month and name of RequestData.

Quick Summary

With @BeanParam you can inject request parameters into beans. This is especially useful if you have more than a few parameters. Inside bean parameters all other parameter annotations can be used.

• You can find the example source code on GitHub.