§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(new Long(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 = new Integer(data.get("from")[0]);
to = new Integer(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();
}Next: Extending Play
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