Do fast isValidFile checks first for dynamically loaded iosps to impr…

…ove performance

cdm/core/src/main/java/ucar/nc2/NetcdfFiles.java

@@ -5,6 +5,7 @@
 
 package ucar.nc2;
 
+import com.google.common.collect.Lists;
 import java.io.BufferedInputStream;
 import java.io.ByteArrayOutputStream;
 import java.io.File;
@@ -19,6 +20,7 @@
 import java.nio.channels.OverlappingFileLockException;
 import java.util.ArrayList;
 import java.util.Arrays;
+import java.util.Collections;
 import java.util.List;
 import java.util.ServiceLoader;
 import java.util.zip.GZIPInputStream;
@@ -788,8 +790,12 @@ private static IOServiceProvider getIosp(ucar.unidata.io.RandomAccessFile raf) t
       return new N3iospNew();
 
     } else {
-      // look for dynamically loaded IOSPs
-      for (IOServiceProvider loadedSpi : ServiceLoader.load(IOServiceProvider.class)) {
+      // look for dynamically loaded IOSPs, and sort before using
+      final ServiceLoader<IOServiceProvider> iosps = ServiceLoader.load(IOServiceProvider.class);
+      final List<IOServiceProvider> sortedIosps = Lists.newArrayList(iosps);
+      Collections.sort(sortedIosps);
+
+      for (IOServiceProvider loadedSpi : sortedIosps) {
         if (loadedSpi.isValidFile(raf)) {
           Class c = loadedSpi.getClass();
           try {

cdm/core/src/main/java/ucar/nc2/iosp/IOServiceProvider.java

@@ -35,7 +35,7 @@
  *
  * @author caron
  */
-public interface IOServiceProvider {
+public interface IOServiceProvider extends Comparable<IOServiceProvider> {
 
   /**
    * Check if this is a valid file for this IOServiceProvider.
@@ -243,4 +243,28 @@ long readToOutputStream(Variable v2, Section section, OutputStream out)
    */
   String getFileTypeDescription();
 
+  /**
+   * Used to determine the ordering for dynamically loaded IOServiceProviders.
+   */
+  enum SortGroup {
+    GROUP_1, LAST_GROUP,
+  }
+
+  /**
+   * Get the SortGroup for this IOServiceProvider. This determines the order in which the dynamically loaded
+   * IOServiceProviders are checked to see if they can open a file with isValidFile().
+   *
+   * @return SortGroup, by default the SortGroup.LAST_GROUP will be used.
+   */
+  default SortGroup getSortGroup() {
+    return SortGroup.LAST_GROUP;
+  }
+
+  /**
+   * Used the SortGroup to determine the ordering for dynamically loaded IOServiceProviders.
+   */
+  @Override
+  default int compareTo(IOServiceProvider other) {
+    return getSortGroup().compareTo(other.getSortGroup());
+  }
 }

cdm/zarr/src/main/java/ucar/nc2/iosp/zarr/ZarrIosp.java

@@ -38,6 +38,16 @@ public boolean isValidFile(RandomAccessFile raf) {
     return raf.isDirectory();
   }
 
+  /**
+   * Set the SortGroup to GROUP_1 so this IOSP will be checked first, since `isValidFile()` is a quick check
+   *
+   * @return SortGroup.GROUP_1
+   */
+  @Override
+  public SortGroup getSortGroup() {
+    return SortGroup.GROUP_1;
+  }
+
   @Override
   public String getFileTypeId() {
     return fileTypeId;