8241389: URLConnection::getHeaderFields returns result inconsistent with getHeaderField/Key for FileURLConnection, FtpURLConnection

Reviewed-by: dfuchs

src/java.base/share/classes/sun/net/www/URLConnection.java

@@ -25,6 +25,7 @@
 
 package sun.net.www;
 
+import java.io.IOException;
 import java.net.URL;
 import java.util.*;
 
@@ -109,6 +110,26 @@ public abstract class URLConnection extends java.net.URLConnection {
         return properties == null ? null : properties.findValue(name);
     }
 
+
+    Map<String, List<String>> headerFields;
+
+    @Override
+    public Map<String, List<String>> getHeaderFields() {
+        if (headerFields == null) {
+            try {
+                getInputStream();
+                if (properties == null) {
+                    headerFields = super.getHeaderFields();
+                } else {
+                    headerFields = properties.getHeaders();
+                }
+            } catch (IOException e) {
+                return super.getHeaderFields();
+            }
+        }
+        return headerFields;
+    }
+
     /**
      * Return the key for the nth header field. Returns null if
      * there are fewer than n fields.  This can be used to iterate

src/java.base/share/classes/sun/net/www/protocol/file/FileURLConnection.java

@@ -138,6 +138,11 @@ public class FileURLConnection extends URLConnection {
         }
     }
 
+    public Map<String,List<String>> getHeaderFields() {
+        initializeHeaders();
+        return super.getHeaderFields();
+    }
+
     public String getHeaderField(String name) {
         initializeHeaders();
         return super.getHeaderField(name);