After JDK-7026262 fix, the behavior of HttpExchange changed when calling sendResponseHeaders(N, -1) first and then reading the InputStream obtained from getRequestBody():

static class MyHandler implements HttpHandler {
    @Override
    public void handle(HttpExchange t) {
        try {
            t.sendResponseHeaders(200, -1);
            InputStream is = t.getRequestBody();
            byte[] in = is.readAllBytes();
            System.out.print(new String(in));
            t.close();
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

Before JDK-7026262, the request body InputStream could be read successfully.
After the fix, it throws "java.io.IOException: Stream is closed" because ExchangeImpl.sendResponseHeaders() now calls ExchangeImpl.close() if contentLen is -1.

HttpServerTest.java reproducer is attached.

Although reading the request body after calling sendResponseHeaders() is not a typical life-cycle pattern according to the HttpExchange specification, it does not appear to be explicitly prohibited.
Moreover, it still works when sendResponseHeaders() is called with a non-negative contentLen.

A simple workaround is to read the request body before sending response headers.