URLEncoder not able to translate space character

This behaves as expected. The URLEncoder implements the HTML Specifications for how to encode URLs in HTML forms.

From the javadocs:

This class contains static methods for converting a String to the application/x-www-form-urlencoded MIME format.

and from the HTML Specification:

application/x-www-form-urlencoded

Forms submitted with this content type must be encoded as follows:

1. Control names and values are escaped. Space characters are replaced by `+'

You will have to replace it, e.g.:

System.out.println(java.net.URLEncoder.encode("Hello World", "UTF-8").replace("+", "%20"));

A space is encoded to %20 in URLs, and to + in forms submitted data (content type application/x-www-form-urlencoded). You need the former.

Using Guava:

dependencies {     compile 'com.google.guava:guava:23.0'     // or, for Android:     compile 'com.google.guava:guava:23.0-android'}

You can use UrlEscapers:

String encodedString = UrlEscapers.urlFragmentEscaper().escape(inputString);

Don't use String.replace, this would only encode the space. Use a library instead.

This class perform application/x-www-form-urlencoded-type encoding rather than percent encoding, therefore replacing with + is a correct behaviour.

From javadoc:

When encoding a String, the following rules apply:

• The alphanumeric characters "a" through "z", "A" through "Z" and "0" through "9" remain the same.
• The special characters ".", "-", "*", and "_" remain the same.
• The space character " " is converted into a plus sign "+".
• All other characters are unsafe and are first converted into one or more bytes using some encoding scheme. Then each byte is represented by the 3-character string "%xy", where xy is the two-digit hexadecimal representation of the byte. The recommended encoding scheme to use is UTF-8. However, for compatibility reasons, if an encoding is not specified, then the default encoding of the platform is used.