You may required to save API response in to an external file like text or JSON etc file for future reference or as a proof. In this post, we will concentrate on saving response in a text file.

Rest Assured provides below methods to get response as:-

1. As byte array :- asByteArray()
2. As input stream :- asInputStream()
3. As string :- asString()

All above methods output can be used to write in to text file.

Rest Assured Code:-

package RestfulBooker.extractResponse;
 
import java.io.File;
import java.io.IOException;
import java.io.InputStream;
import com.google.common.io.Files;
 
import io.restassured.RestAssured;
import io.restassured.http.ContentType;
import io.restassured.response.Response;
import io.restassured.specification.RequestSpecification;
 
public class WriteResponseInTextFile {
	
	
	public static void main(String[] args) throws IOException {
		
		// There is no need to add escape character manually. Just paste string within double
		// quotes. It will automatically add escape sequence as required.
		String jsonString = "{\"username\" : \"admin\",\"password\" : \"password123\"}";
		
		// Create a request specification
		RequestSpecification request= RestAssured.given();
		
		// Setting content type to specify format in which request payload will be sent.
		// ContentType is an ENUM.
		request.contentType(ContentType.JSON);
		//Adding URI
		request.baseUri("https://restful-booker.herokuapp.com/auth");
		// Adding body as string
		request.body(jsonString);
		
		// Calling POST method on URI. After hitting we get Response
		Response response = request.post();
		
		// Getting response as a string and writing in to a file
		String responseAsString = response.asString();
		// Converting in to byte array before writing
		byte[] responseAsStringByte = responseAsString.getBytes();
		// Creating a target file
		File targetFileForString = new File("src/main/resources/targetFileForString.txt");
		// Writing into files
		Files.write(responseAsStringByte, targetFileForString);
		
		
		// Getting response as input stream and writing in to a file
		InputStream responseAsInputStream = response.asInputStream();
		// Creating a byte array with number of bytes of input stream (available() method)
		byte[] responseAsInputStreamByte = new byte[responseAsInputStream.available()];
		// Reads number of bytes from the input stream and stores them into the byte array responseAsInputStreamByte.
		responseAsInputStream.read(responseAsInputStreamByte);
		// Creating a target file
		File targetFileForInputStream = new File("src/main/resources/targetFileForInputStream.txt");
		// Writing into files
		Files.write(responseAsInputStreamByte, targetFileForInputStream);
		
		// Directly getting a byte array
		byte[] responseAsByteArray = response.asByteArray();
		// Creating a target file
		File targetFileForByteArray = new File("src/main/resources/targetFileForByteArray.txt");
		// Writing into files
		Files.write(responseAsByteArray, targetFileForByteArray);
			    
			
			  
			    
	}
 
}

Output:-

Refresh the project folder if you are using Eclipse. You should see three files as below:-

Open a file you should see it has stored response as below:-

You may be thinking which way is more optimal if you want to write in to a file. If you notice when we get response as String or inputStream , we must need to convert them to Byte array before writing in to a file. In third way we are directly getting Byte Array. So third way is more optimal.