[SalesForce] “POST requires content-length error” occur when i am trying to call custom Rest API @HttpDelete Resource

Thanks Keith C, i have make it correct..... actually it was incorrect here not on my console.

and i also found the issue:

actually i am using package name as MyPackageAC at the server account ... that's why error occur. change the end point: request.setEndPoint('https://ap1.salesforce.com/services/apexrest/MyPackageAC/ServerCustomRestApi');

This is possible in java. I tried your code and it is working. As per my observation only thing which could be culprit here is the uri. Below is the code snippet where I have mentioned uri directly.

import java.io.FileNotFoundException;
import java.io.FileReader;
import java.io.IOException;

import org.apache.commons.httpclient.HttpClient;
import org.apache.commons.httpclient.methods.PostMethod;
import org.apache.commons.httpclient.methods.StringRequestEntity;
import org.json.simple.parser.JSONParser;
import org.json.simple.parser.ParseException;


public class Main {

        public static void main(String[] args) throws FileNotFoundException, IOException, ParseException {
            JSONParser parser = new JSONParser();

               // Parser parsing  JSON File having multiple records
               Object obj = parser.parse(new FileReader("JsonData.json"));

               HttpClient httpclient = new HttpClient();
               PostMethod mypost = new PostMethod("https://kmforce-dev-ed.my.salesforce.com/services/data/v34.0/composite/tree/Account/");
               String jsonText = obj.toString();
               System.out.println("\n_JSON TEXT=" + jsonText);
               mypost.setRequestHeader("Authorization", "OAuth " +"<myssessionid>"); 
               mypost.setRequestEntity(new StringRequestEntity(jsonText, "application/json", "UTF-8"));
               int response=httpclient.executeMethod(mypost);
               System.out.println(response);
               System.out.println("Response-->"+mypost.getResponseBodyAsString());
        }
}

Below is the output:

{
    "hasErrors": false,
    "results": [
        {
            "referenceId": "ref1",
            "id": "0019000001bslYJAAY"
        },
        {
            "referenceId": "ref2",
            "id": "0019000001bslYKAAY"
        },
        {
            "referenceId": "ref3",
            "id": "0019000001bslYLAAY"
        },
        {
            "referenceId": "ref4",
            "id": "0019000001bslYMAAY"
        }
    ]
}

Let me know if you face any issue here.