What's the proper way to escape URL variables with Spring's RestTemplate when calling a Spring RestController?

Question

When calling RestTemplate.exchange to do a get request, such as:

String foo = "fo+o";
String bar = "ba r";
restTemplate.exchange("http://example.com/?foo={foo}&bar={bar}", HttpMethod.GET, null, foo, bar)

what's the proper to have the URL variables correctly escaped for the get request?

Specifically, how do I get pluses (+) correctly escaped because Spring is interpreting as spaces, so, I need to encode them.

I tried using UriComponentsBuilder like this:

String foo = "fo+o";
String bar = "ba r";
UriComponentsBuilder ucb = UriComponentsBuilder.fromUriString("http://example.com/?foo={foo}&bar={bar}");
System.out.println(ucb.build().expand(foo, bar).toUri());
System.out.println(ucb.build().expand(foo, bar).toString());
System.out.println(ucb.build().expand(foo, bar).toUriString());
System.out.println(ucb.build().expand(foo, bar).encode().toUri());
System.out.println(ucb.build().expand(foo, bar).encode().toString());
System.out.println(ucb.build().expand(foo, bar).encode().toUriString());
System.out.println(ucb.buildAndExpand(foo, bar).toUri());
System.out.println(ucb.buildAndExpand(foo, bar).toString());
System.out.println(ucb.buildAndExpand(foo, bar).toUriString());
System.out.println(ucb.buildAndExpand(foo, bar).encode().toUri());
System.out.println(ucb.buildAndExpand(foo, bar).encode().toString());
System.out.println(ucb.buildAndExpand(foo, bar).encode().toUriString());

and that printed:

http://example.com/?foo=fo+o&bar=ba%20r
http://example.com/?foo=fo+o&bar=ba r
http://example.com/?foo=fo+o&bar=ba r
http://example.com/?foo=fo+o&bar=ba%20r
http://example.com/?foo=fo+o&bar=ba%20r
http://example.com/?foo=fo+o&bar=ba%20r
http://example.com/?foo=fo+o&bar=ba%20r
http://example.com/?foo=fo+o&bar=ba r
http://example.com/?foo=fo+o&bar=ba r
http://example.com/?foo=fo+o&bar=ba%20r
http://example.com/?foo=fo+o&bar=ba%20r
http://example.com/?foo=fo+o&bar=ba%20r

The space is correctly escaped in some instances, but the plus is never escaped.

I also tried UriTemplate like this:

String foo = "fo+o";
String bar = "ba r";
UriTemplate uriTemplate = new UriTemplate("http://example.com/?foo={foo}&bar={bar}");
Map<String, String> vars = new HashMap<>();
vars.put("foo", foo);
vars.put("bar", bar);
URI uri = uriTemplate.expand(vars);
System.out.println(uri);

with the exact same result:

http://example.com/?foo=fo+o&bar=ba%20r

Answer 1

Apparently, the correct way of doing this is by defining a factory and changing the encoding mode:

String foo = "fo+o";
String bar = "ba r";
DefaultUriBuilderFactory factory = new DefaultUriBuilderFactory();
factory.setEncodingMode(DefaultUriBuilderFactory.EncodingMode.VALUES_ONLY);
URI uri = factory.uriString("http://example.com/?foo={foo}&bar={bar}").build(foo, bar);
System.out.println(uri);

That prints out:

http://example.com/?foo=fo%2Bo&bar=ba%20r

This is documented here: https://docs.spring.io/spring/docs/current/spring-framework-reference/web.html#web-uri-encoding