Use one of the constructors with more than one argument, like:
URI uri = new URI(
"http",
"search.barnesandnoble.com",
"/booksearch/first book.pdf",
null);
URL url = uri.toURL();
//or String request = uri.toString();
(the single-argument constructor of URI does NOT escape illegal characters)
Only illegal characters get escaped by above code - it does NOT escape non-ASCII characters (see fatih's comment).
The toASCIIString method can be used to get a String only with US-ASCII characters:
URI uri = new URI(
"http",
"search.barnesandnoble.com",
"/booksearch/é",
null);
String request = uri.toASCIIString();
For an URL with a query like http://www.google.com/ig/api?weather=São Paulo, use the 5-parameter version of the constructor:
URI uri = new URI(
"http",
"www.google.com",
"/ig/api",
"weather=São Paulo",
null);
String request = uri.toASCIIString();
