replace HashMap with ConcurrentHashMap and use byte[]

direct-file/backend/src/main/java/gov/irs/directfile/api/io/memory/MemoryIOLocation.java

@@ -3,8 +3,8 @@
 import java.io.ByteArrayInputStream;
 import java.io.IOException;
 import java.io.InputStream;
-import java.util.HashMap;
 import java.util.Map;
+import java.util.concurrent.ConcurrentHashMap;
 
 import lombok.extern.slf4j.Slf4j;
 
@@ -18,36 +18,18 @@ public class MemoryIOLocation implements IIOLocation {
     // don't use it as a cache, because the stream copy isn't performant.
     // it is still better than getting files off of disk.
     // Locations are meant for heavy IO operations
-    Map<String, InputStream> writtenData;
+    Map<String, byte[]> writtenData;
 
     public MemoryIOLocation() {
-        writtenData = new HashMap<>();
+        writtenData = new ConcurrentHashMap<>();
     }
 
     @Override
     public InputStream read(String location) throws IOLocationException {
-        if (writtenData.containsKey(location)) {
-            var stream = writtenData.get(location);
-            // we might hit a case where multiple threads try to read from the same stream
-            // at the same time.  We don't want a partial read.  There are better ways of solving
-            // this, but this is a quick way.  If this performs anything like dotnet, this will show
-            // itself as a bottleneck by increasing the background thread count beyond normal levels.
-            // The read should be fast enough that it doesn't really matter, but I'd like to be certain.
-            // P.S. I don't care about writing as much in this context, but if write becomes important
-            // then you will need to sync that too.
-            synchronized (stream) {
-                try {
-                    // We cannot hand out the original stream, as we don't know the stateCode
-                    // they will return it in.  We want to have it fresh and ready for each call
-                    // so we pass out a copy and reset ours for the next call
-                    log.info("In memory information found at {}!  Copying bytes to a new buffer", location);
-                    var bytes = stream.readAllBytes();
-                    stream.reset();
-                    return new ByteArrayInputStream(bytes);
-                } catch (IOException e) {
-                    throw new IOLocationException("In memory location couldn't copy bytes to allow reading", e);
-                }
-            }
+        byte[] bytes = writtenData.get(location);
+        if (bytes != null) {
+            log.info("In memory information found at {}!  Copying bytes to a new buffer", location);
+            return new ByteArrayInputStream(bytes);
         }
         throw new IOLocationException(
                 String.format("Did not write data to in memory location %s before reading", location));
@@ -64,9 +46,8 @@ public void write(String location, InputStream payloadStream) throws IOLocationE
         } catch (IOException e) {
             throw new IOLocationException("Could not write bytes to in memory stream", e);
         }
-        var stream = new ByteArrayInputStream(bytes);
         log.info("Adding in memory byte stream at {}", location);
-        writtenData.put(location, stream);
+        writtenData.put(location, bytes);
     }
 
     @Override