Documentation

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§Custom Routing

Play provides a mechanism to bind types from path or query string parameters.

§PathBindable

PathBindable allows to bind business objects from the URL path; this means we’ll be able to define routes like /user/3 to call an action such as the following:

§controller

public Result user(User user) {
  return ok(user.name);
}

The user parameter will automatically be retrieved using the id extracted from the URL path, e.g. with the following route definition:

§/conf/routes

GET     /user/:user            controllers.BinderApplication.user(user: javaguide.binder.models.User)

Any type T that implements PathBindable can be bound to/from a path parameter.
It defines abstract methods bind (build a value from the path) and unbind (build a path fragment from a value).

For a class like:

public class User implements PathBindable<User> {

  public Long id;
  public String name;

A simple example of the binder’s use binding the :id path parameter:

@Override
public User bind(String key, String id) {

  // findById meant to be lightweight operation
  User user = findById(Long.valueOf(id));
  if (user == null) {
    throw new IllegalArgumentException("User with id " + id + " not found");
  }
  return user;
}

@Override
public String unbind(String key) {
  return String.valueOf(id);
}

In this example findById method is invoked to retrieve User instance.

Note: in a real application such method should be lightweight and not involve e.g. DB access, because the code is called on the server IO thread and must be totally non-blocking. You would therefore for example use simple objects identifier as path bindable, and retrieve the real values using action composition.

§QueryStringBindable

A similar mechanism is used for query string parameters; a route like /age can be defined to call an action such as:

§controller

public Result age(AgeRange ageRange) {
  return ok(String.valueOf(ageRange.from));
}

The age parameter will automatically be retrieved using parameters extracted from the query string e.g. /age?from=1&to=10

Any type T that implements QueryStringBindable can be bound to/from query one or more query string parameters. Similar to PathBindable, it defines abstract methods bind and unbind.

For a class like:

public class AgeRange implements QueryStringBindable<AgeRange> {

  public Integer from;
  public Integer to;

A simple example of the binder’s use binding the :from and :to query string parameters:

@Override
public Optional<AgeRange> bind(String key, Map<String, String[]> data) {

  try {
    from = Integer.valueOf(data.get("from")[0]);
    to = Integer.valueOf(data.get("to")[0]);
    return Optional.of(this);

  } catch (Exception e) { // no parameter match return None
    return Optional.empty();
  }
}

@Override
public String unbind(String key) {
  return new StringBuilder().append("from=").append(from).append("&to=").append(to).toString();
}

All binders Play provides automatically apply form URL encoding in their unbind methods, so all special characters are safely URL encoded. This doesn’t happen automatically however when implementing custom binders, therefore make sure to encode key/value parts if necessary:

@Override
public String unbind(String key) {
  String identifierEncoded;
  try {
    identifierEncoded = URLEncoder.encode(identifier, "utf-8");
  } catch (Exception e) {
    // Should never happen
    identifierEncoded = identifier;
  }

  return new StringBuilder()
      // Key string doesn't contain special characters and doesn't need form URL encoding:
      .append("identifier")
      .append('=')
      // Value string may contain special characters, do encode:
      .append(identifierEncoded)
      .toString();
}

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