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java.net.URL/URI consider an invalid URL as valid

Not all invalid urls will be consider as invalid by java.net.URL/URI
An example: http:www.google.com
Is it a bug or is it a feature?
Or is maybe the string above a valid url?

Without //, the URL is treated as a relative URL, that needs a context to be useful.
If you try using it, you'll get this error:
IllegalArgumentException: protocol = http host = null

How to fix the URI does not specify a valid host name in ClientProtocolException:

When I execute the elastic search java API using jest client, I face the following error
org.apache.http.client.ClientProtocolException: URI does not specify a valid host name:localhost:9200/index/type/_search
I tries various possibilities to fix this error, but I am stuck. How can I fix this?

You just need to add http:// at the beginning of the URI.

If you are seeing the same error in JMeter while you want to use a response Json key value in another variable(by creating a new HTTP Request) then use JSON Extractor instead of Regular Expression extractor. Thread Group->Right click and Add->Post Processor->JSON Extractor)
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how to get URL from address bar in JSP

Lets say I hit
http://localhost/webapp/wcs/stores/servlet/en/marksandspencer/l/women/dresses/party-and-cocktail-dresses
and this internally redirects me to custom 404.jsp page, But URL remain same in address bar.
I tried this code - <%= request.getAttribute("javax.servlet.forward.request_uri") %>; and it's returning me the path of 404.jsp
How can I get the entered URL which is there in address bar?

Use request.getAttribute("javax.servlet.error.request_uri") to get URI of requested page that not found (404 error). Check this: https://tomcat.apache.org/tomcat-7.0-doc/servletapi/constant-values.html
When error raised (because of some reason such as page not found (404), Internal Server Error (500), ...), the servlet engine will FORWARD the request to corresponding error page (configured in web.xml) using ERROR dispatcher type, NOT FORWARD dispatcher type so that is the reason we must use javax.servlet.error.request_uri, NOT use javax.servlet.forward.request_uri

I think you were close. javax.servlet.forward.request_uri is for normal forwarding, but for 404, you need javax.servlet.error.request_uri.

You can use :
String url = request.getRequestURL().toString();
but this doesn't hold Query String. So, to get query string, you may call
request.getQueryString()

You can do this to get the whole URL including parameters.
request.getRequestURL()+""+request.getQueryString();

use request.getHeader("Referer").
referer gives a url from where you redirected.

Android java - Regex to check whether the url starts with https or http

I am getting some urls from server that contains some images. Some urls start with http and some start with https. I need to check if the url string contain http, then put an s in that string after p, and if it contains https then do nothing.

if (urlString.startsWith("http://")) {
urlString = urlString.replaceFirst("http", "https");
}

Http request returning different response in browser

I'm getting a JSON object from a server, When I enter the following generated URL into my browser I get a response with "num_match": 18, however when running in my app I get a JSON object with "num_matches": 2.
The URL object is created like this
URL request;
request = new URL(url);
and connection like this:
HttpURLConnection connection = (HttpURLConnection) request.openConnection();
connection.setConnectTimeout(MAX_TIME);
connection.setReadTimeout(MAX_TIME);
url is a String and I am copying the string contents into my browser to test.
The string is:
http://search.3taps.com/?auth_token=xxxxxxxxxxxxxxxxxx&retvals=heading,body,timestamp,external_url,images,price&rpp=100&source=BKPGE|CRAIG|EBAYC|INDEE|KIJIJ&category=PWSM&radius=200mi&lat=26.244&long=-80.2&annotations={age:18 OR age:19 OR age:20 OR age:21 OR age:22}
The URL object has the following fields
query:
auth_token=xxxxxxxxxxxxxxxxxx&retvals=heading,body,timestamp,external_url,images,price&rpp=100&source=BKPGE|CRAIG|EBAYC|INDEE|KIJIJ&category=PWSM&radius=200mi&lat=26.244&long=-80.2&annotations={age:18 OR age:19 OR age:20 OR age:21 OR age:22}
file:
/?auth_token=xxxxxxxxxxxxxxxxxx&retvals=heading,body,timestamp,external_url,images,price&rpp=100&source=BKPGE|CRAIG|EBAYC|INDEE|KIJIJ&category=PWSM&radius=200mi&lat=26.244&long=-80.2&annotations={age:18 OR age:19 OR age:20 OR age:21 OR age:22}
host:
search.3taps.com
The response comes back as "success":true on both but with a discrepancy in the object returned. I don't know much about http, what could be causing this?
UPDATE: On further testing it seems like there is only a problem when the annotations entry is present
annotations={age:18 OR age:19 OR age:20 OR age:21 OR age:22}
seems to be causing the problem.

Make sure you are encoding the URL request correctly when you are setting the URL for the server. The spaces, braces, and colons all need to be appropriately escaped. Spaces should be %20, etc. This may help: HTTP URL Address Encoding in Java
Old Answer.... Comments indicate this does not affect the result... so moving down.
It is quite possible that the server is changing it's behaviour based on the type of 'browser' you are reporting yourself to be. When connecting to an HTTP server you tell the server what your UserAgent is (typically for a browser it is something like "Internet Explorer ...." or "Mozilla ..." or "Google Chome ...". The Server will often tailor the results of a request to suite the User Agent (different javascript files and HTML codes go to IE, etc.). This is also how servers re-direct mobile devices to a mobile-friendly version of a site.
It is quite possible that the server is changing it's response to match your UserAgent exposed by your Java code, (which by decault is something like "Java/1.7.0". You can change this value a few ways. Have a look at this question Setting user agent of a java URLConnection and try to run your program with the Mozilla agent, and see if you get different results.