How to Use cURL in Java

1. cURL in Java
2. Different Ways to Use cURL in Java

Today, we will learn about cURL in Java. We will also learn how to use cURL with ProcessBuilder and Runtime.getRuntime.

cURL in Java

The cURL is a networking tool that transfers the data between the cURL client and server. The cURL uses the protocols like HTTP, FTP, TELNET, and SCP.

The cURL works similar to the core java’s java.net.URLConnection package or Apache’s ApacheHttpClient. However, the cURL works in commands, so we may need to use ProcessBuilder or Runtime.getRuntime() in Java.

Different Ways to Use cURL in Java

First, make sure the cURL is installed on your system. Then, download the cURL installer from these links and install it on your system.

• cURL for Windows
• cURL for Windows

Method 1: Use cURL With ProcessBuilder

Once cURL is installed on the system, we can use it in Java. Here is a simple example of how to use cURL in Java:

String Demo_Command = "curl -X GET https://localhost/get?delft1=stack1&delft2=stack2";
ProcessBuilder Process_Builder = new ProcessBuilder(Demo_Command.split(" "));

The above code executes the cURL command with a get request on the given server link. We also need to provide the system path for cURL; otherwise, it will not work.

String Demo_Command = "curl -X GET https://localhost/get?delft1=stack1&delft2=stack2";
ProcessBuilder Process_Builder = new ProcessBuilder(Demo_Command.split(" "));
Process_Builder.directory(new File("/home/"));
Process Demo_process = Process_Builder.start();

Now we can get the input stream from the process, and after the processing is complete, we can get the exit code and destroy the process instance.

String Demo_Command = "curl -X GET https://localhost/get?delft1=stack1&delft2=stack2";
ProcessBuilder Process_Builder = new ProcessBuilder(Demo_Command.split(" "));
Process_Builder.directory(new File("/home/"));
Process Demo_process = Process_Builder.start();

InputStream Input_Stream = Demo_process.getInputStream();
int Exit_Code = Demo_process.exitValue();
System.out.println(Exit_Code);
Demo_process.destroy();

For additional cURL commands, we can reuse the ProcessBuilder or pass the commands as an array.

Method 2: Use cURL With Runtime.getRuntime

Another method to run commands in Java is Runtime.getRuntime() to get the instance of the process class. The Runtime.getRuntime() is good alternative to use cURL in Java.

Let’s try to execute cURL using Runtime.getRuntime in Java:

String Demo_Command = "curl -X POST https://localhost/post --data delft1=stack1&delft2=stack2";
Process Demo_process = Runtime.getRuntime().exec(Demo_Command);

The code above sends a post request using the cURL and Runtime.getRuntime methods. Now we can get the InputStream with the same method described above.

String Demo_Command = "curl -X POST https://localhost/post --data delft1=stack1&delft2=stack2";
Process Demo_process = Runtime.getRuntime().exec(Demo_Command);
InputStream Input_Stream = Demo_process.getInputStream();
Demo_process.destroy();

Remember, if the instances are no longer required, the system resources should be released using the destroy() method on the process instances.