Java EE 8 MVC: Working with bean parameters

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.