How to add headers based on multiple conditions to HttpRequest Java 11?

Question

I'm learning the java.net.http api, trying to download a file given a range of bytes already downloaded. For this the range header can be used (supposing the server supports such feature).

Using org.apache.http.client.methods.HttpGet I can do this:

HttpGet httpGet= new HttpGet("http://exampleURL.com/aFile");
if (myFile.length() > 0) {
            httpGet.addHeader("Range", "bytes=" + myFile.length() + "-"+totalBytes));
}
httpGet.addHeader("xxxx", "yyyy");//ok

Now with HttpRequest I can't add new headers dynamically, I have to create a new whole HttpRequest:

HttpRequest request = null;
if (myFile.length() > 0) {
  request = HttpRequest.newBuilder()
      .uri(URI.create("http://exampleURL.com/aFile"))
      .header("Range","bytes="+myFile.length() +"-"+ totalBytes)
      .build();
}else{
  request = HttpRequest.newBuilder()
      .uri(URI.create("http://exampleURL.com/aFile"))
      .build();
}
request.header("xxxx","yyyyy")//Can't do this anymore

I there a way add them dynamically?

I see that the docs say:

Once built an HttpRequest is immutable, and can be sent multiple times.

But what's the point to be immutable? What if I need for any reason to modify the headers?

Reference:

https://openjdk.java.net/groups/net/httpclient/intro.html

Instead of chaining methods, you can store the `HttpRequest.Builder` instance and call the various methods separately. Only call `build` right before you send the request. — Albjenow, Oct 11 '19 at 10:18

score 6 · Accepted Answer · answered Oct 11 '19 at 11:12

As Albjenow suggested you can create the builder with common fields first and then build the final request after applying your logic. It would look like :

HttpRequest.Builder requestBuilder = HttpRequest.newBuilder()
                .uri(URI.create("http://exampleURL.com/aFile"));

if (myFile.length() > 0) {
    requestBuilder.header("Range","bytes="+myFile.length() +"-"+ totalBytes);
}

requestBuilder.header("xxxx","yyyyy");

HttpRequest request = requestBuilder.build();

score 2 · Answer 2 · answered Oct 11 '19 at 10:33

An alternate way could be determining all the possible headers before completing the build chain for the HttpRequest and using them with HttpRequest.Builder#headers as:

List<String> headers = new ArrayList<>();
if (myFile.length() > 0) {
    headers.add("Range");
    headers.add("bytes=" + myFile.length() + "-" + totalBytes);
}

HttpRequest request = HttpRequest.newBuilder()
        .uri(URI.create("http://exampleURL.com/aFile"))
        .headers(headers.toArray(String[]::new))
        .build();

How to add headers based on multiple conditions to HttpRequest Java 11?

2 Answers2