{"id":392,"date":"2014-06-29T12:06:07","date_gmt":"2014-06-29T04:06:07","guid":{"rendered":"https:\/\/www.techcoil.com\/blog\/?p=392"},"modified":"2018-09-04T13:26:28","modified_gmt":"2018-09-04T05:26:28","slug":"how-to-send-http-get-request-with-java-without-using-any-external-libraries","status":"publish","type":"post","link":"https:\/\/www.techcoil.com\/blog\/how-to-send-http-get-request-with-java-without-using-any-external-libraries\/","title":{"rendered":"How to send HTTP GET request with Java without using any external libraries"},"content":{"rendered":"

There was this time when I need to build a program to check whether my web server is running fine. To determine that my web server is running fine, I wrote a Java applet that sends a HTTP GET to one of my web resources when the applet runs for the first time. And to keep the applet light, I look into Java in-built features for sending HTTP GETs to my server. This post documents a proof of concept that I did to communicate with my server endpoint via HTTP GET using Java in-built features.<\/p>\n

Defining the server endpoint to connect to<\/h3>\n

I chose to use my robots.txt<\/code> for probing whether my server is running fine. To probe my server, I write the following codes:<\/p>\n

\r\nURL robotsUrl = new URL("http:\/\/www.techcoil.com\/robots.txt");\r\nHttpURLConnection urlConnection = (HttpURLConnection) robotsUrl.openConnection();  \r\n<\/pre>\n
I first create a java.net.URL<\/code> object to my robots.txt<\/code>. I then call robotsUrl.openConnection()<\/code> to get a java.net.HttpURLConnection<\/code> object that will allow me to send a HTTP request to my server to get robots.txt<\/code> as a HTTP response.<\/p>\n
Configuring the HttpURLConnection<\/h3>\n
Unlike sending a HTTP POST to the server endpoint<\/a>, no additional configurations is needed for the HttpURLConnection<\/code> object as the default request method is set to HTTP GET and we do not need to write anything as the HTTP request body.<\/p>\n
Sending the HTTP request and verifying the HTTP response<\/h3>\n
The HTTP request will be sent to the server when we read from our HttpURLConnection<\/code> object. As such, the next step will be to read the HTTP response body from urlConnection<\/code> and verify the contents. The contents should contain the string \"Sitemap: http:\/\/www.techcoil.com\/sitemap-index.xml\". <\/p>\n
To do so, I wrote the following codes:<\/p>\n
\r\nScanner httpResponseBodyScanner = new Scanner(urlConnection.getInputStream());\r\n\r\n\/\/ Use a ByteArrayOutputStream to store the contents of the HTTP response body\r\nByteArrayOutputStream responseBodyBaos = new ByteArrayOutputStream();\r\nwhile(httpResponseBodyScanner.hasNextLine()) {\r\n\tresponseBodyBaos.write(httpResponseBodyScanner.nextLine().getBytes());\r\n}\r\nresponseBodyBaos.close();\r\nhttpResponseBodyScanner.close();\r\n\r\n\/\/ Verify contents of robots.txt\r\nString robotsContent = responseBodyBaos.toString();\r\nif (robotsContent.trim().equals("Sitemap: http:\/\/www.techcoil.com\/sitemap-index.xml")) {\r\n\tSystem.out.println("Able to retrieve robots.txt from server. Server is running fine.");\r\n}\r\nelse {\r\n\tSystem.out.println("Not able to retrive robots.txt from server.");\r\n}\r\n<\/pre>\n
I first layered a java.util.Scanner<\/code> object to the input stream of urlConnection<\/code> to allow my codes to read the HTTP response body that my server sends back to me. I then use a java.io.ByteArrayOutputStream<\/code> object to record the contents of the HTTP response body. <\/p>\n
After all the contents of my HTTP response body is recorded in the java.io.ByteArrayOutputStream<\/code> object, I proceed to verify the contents, trimming any leading or trailing white spaces. If the trimmed contents is the string \"Sitemap: http:\/\/www.techcoil.com\/sitemap-index.xml\", I output \"Able to retrieve robots.txt from server. Server is running fine.\" to console. If not, I output \"Not able to retrive robots.txt from server.\" to console.<\/p>\n
A simple console application that sends a HTTP GET request to a server endpoint at Techcoil to check whether Techcoil is running fine<\/h3>\n
To sum up the points covered in this post, I put together the following class which can be used to build a console application that checks the content of http:\/\/www.techcoil.com\/robots.txt to determine whether Techcoil is running fine:<\/p>\n
\r\nimport java.io.BufferedWriter;\r\nimport java.io.ByteArrayOutputStream;\r\nimport java.io.IOException;\r\nimport java.io.OutputStreamWriter;\r\nimport java.net.HttpURLConnection;\r\nimport java.net.URL;\r\nimport java.util.Scanner;\r\n\r\npublic class Program {\r\n\r\n\tpublic static void main(String[] args) {\r\n\t\t\r\n\t\tByteArrayOutputStream responseBodyBaos = null;\r\n        Scanner httpResponseBodyScanner = null;\r\n        try {\r\n            \/\/ Define server endpoint\r\n            URL robotsUrl = new URL("http:\/\/www.techcoil.com\/robots.txt");\r\n            HttpURLConnection urlConnection = (HttpURLConnection) robotsUrl.openConnection(); \r\n \r\n            httpResponseBodyScanner = new Scanner(urlConnection.getInputStream());\r\n \r\n            \/\/ Use a ByteArrayOutputStream to store the contents of the HTTP response body\r\n            responseBodyBaos = new ByteArrayOutputStream();\r\n            while(httpResponseBodyScanner.hasNextLine()) {\r\n                responseBodyBaos.write(httpResponseBodyScanner.nextLine().getBytes());\r\n            }\r\n            responseBodyBaos.close();\r\n            httpResponseBodyScanner.close();\r\n \r\n            \/\/ Verify contents of robots.txt\r\n            String robotsContent = responseBodyBaos.toString();\r\n            if (robotsContent.trim().equals("Sitemap: http:\/\/www.techcoil.com\/sitemap-index.xml")) {\r\n                System.out.println("Able to retrieve robots.txt from server. Server is running fine.");\r\n            }\r\n            else {\r\n                System.out.println("Not able to retrive robots.txt from server.");\r\n            }\r\n \r\n        } catch(IOException ioException) {\r\n            System.out.println("IOException occurred while contacting server.");\r\n        } finally {\r\n            if (responseBodyBaos != null) {\r\n            \ttry {\r\n                responseBodyBaos.close();\r\n            \t} catch (IOException ioe) {\r\n            \t\tSystem.out.println("Error while closing response body stream");\r\n            \t}\r\n            }\r\n            if (httpResponseBodyScanner != null) {\r\n                httpResponseBodyScanner.close();\r\n            }\r\n        }\r\n}\r\n<\/pre>\n\n