Java

curl with Variable Substitution in a JSON Request Body

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This example shows how to use variables inside a JSON request body using the {{variable_name}} syntax. When the HTTP request’s Content-Type indicates JSON, Chilkat automatically applies proper JSON escaping to each substituted value, ensuring the resulting JSON remains valid. Java

import com.chilkatsoft.*;

public class ChilkatExample {

  static {
    try {
        System.loadLibrary("chilkat");
    } catch (UnsatisfiedLinkError e) {
      System.err.println("Native code library failed to load.\n" + e);
      System.exit(1);
    }
  }

  public static void main(String argv[])
  {
    boolean success = false;

    //  Variable names are enclosed between {{ and }}
    //  Important: The variable {{var_name}} should be placed inside the quotes.

    //  This is correct:
    //  curl -X POST https://api.example.com/messages \
    //    -H "Content-Type: application/json" \
    //    -d '{"text":"{{message}}"}'

    //  This is incorrect:
    //    -d '{"text":{{message}}}'

    CkStringBuilder sbCurl = new CkStringBuilder();
    sbCurl.AppendLn("curl -X POST https://api.example.com/messages \\");
    sbCurl.AppendLn("  -H \"Content-Type: application/json\" \\");
    sbCurl.AppendLn("  -d '{\"text\":\"{{message}}\"}'");

    CkHttpCurl curl = new CkHttpCurl();

    //  In this example, the value we'll provide for the "message" variable
    //  will contain chars that require JSON escaping.
    curl.SetVar("message","He said \"Hello, world!\"");

    //  To demonstrate how the variables are replaced, this example does not execute the curl command. 
    //  Instead, it generates the raw HTTP request that would be sent if the curl command were run.
    CkStringBuilder sbRawRequest = new CkStringBuilder();
    success = curl.ToRawRequest(sbCurl.getAsString(),sbRawRequest);
    if (success == false) {
        System.out.println(curl.lastErrorText());
        return;
        }

    System.out.println(sbRawRequest.getAsString());

    //  The output is shown below.
    //  Notice that the quote chars around "Hello World!" are properly JSON escaped.

    //  POST /messages HTTP/1.1
    //  Host: api.example.com
    //  Content-Type: application/json
    //  Content-Length: 36
    //  
    //  {"text":"He said \"Hello, world!\""}
  }
}