basic-lib/src/main/java/com/streamsets/pipeline/stage/origin/http/HttpClientSource.java
private MultivaluedMap<String, Object> resolveHeaders() throws StageException {
    MultivaluedMap<String, Object> requestHeaders = new MultivaluedHashMap<>();
    for (Map.Entry<String, String> entry : conf.headers.entrySet()) {
      List<Object> header = new ArrayList<>(1);
      Object resolvedValue = headerEval.eval(headerVars, entry.getValue(), String.class);
      header.add(resolvedValue);
      requestHeaders.put(entry.getKey(), header);
      hasher.putString(entry.getKey(), Charset.forName(conf.dataFormatConfig.charset));
      hasher.putString(entry.getValue(), Charset.forName(conf.dataFormatConfig.charset));
    }

    return requestHeaders;
  }
private MultivaluedMap<String, Object> resolveHeaders() throws StageException {
    MultivaluedMap<String, Object> requestHeaders = new MultivaluedHashMap<>();
    for (Map.Entry<String, String> entry : conf.headers.entrySet()) {
      List<Object> header = new ArrayList<>(1);
      Object resolvedValue = headerEval.eval(headerVars, entry.getValue(), String.class);
      header.add(resolvedValue);
      requestHeaders.put(entry.getKey(), header);
      hasher.putString(entry.getKey(), Charset.forName(conf.dataFormatConfig.charset));
      hasher.putString(entry.getValue(), Charset.forName(conf.dataFormatConfig.charset));
    }

    return requestHeaders;
  }
Resolves any expressions in the Header value entries of the request.
@return map of evaluated headers to add to the request
@throws StageException if an unhandled error is encountered