8281298: Revise the creation of unmodifiable list

Reviewed-by: redestad

src/java.base/share/classes/javax/net/ssl/SSLParameters.java

@@ -26,12 +26,7 @@
 package javax.net.ssl;
 
 import java.security.AlgorithmConstraints;
-import java.util.Map;
+import java.util.*;
-import java.util.List;
-import java.util.HashMap;
-import java.util.Collection;
-import java.util.Collections;
-import java.util.LinkedHashMap;
 
 /**
  * Encapsulates parameters for an SSL/TLS/DTLS connection. The parameters
@@ -81,8 +76,8 @@ public class SSLParameters {
     private boolean needClientAuth;
     private String identificationAlgorithm;
     private AlgorithmConstraints algorithmConstraints;
-    private Map<Integer, SNIServerName> sniNames = null;
+    private List<SNIServerName> sniNames = null;        // immutable list
-    private Map<Integer, SNIMatcher> sniMatchers = null;
+    private Collection<SNIMatcher> sniMatchers = null;  // immutable collection
     private boolean preferLocalCipherSuites;
     private boolean enableRetransmissions = true;
     private int maximumPacketSize = 0;
@@ -331,22 +326,29 @@ public class SSLParameters {
      * @since 1.8
      */
     public final void setServerNames(List<SNIServerName> serverNames) {
-        if (serverNames != null) {
+        if (this.sniNames == serverNames) {
-            if (!serverNames.isEmpty()) {
+            return;
-                sniNames = new LinkedHashMap<>(serverNames.size());
+        }
+
+        if (serverNames == null) {
+            sniNames = null;
+        } else if (serverNames.isEmpty()) {
+            sniNames = Collections.emptyList();
+        } else {
+            List<Integer> sniTypes = new ArrayList<>(serverNames.size());
+            List<SNIServerName> sniValues = new ArrayList<>(serverNames.size());
             for (SNIServerName serverName : serverNames) {
-                    if (sniNames.put(serverName.getType(),
+                if (sniTypes.contains(serverName.getType())) {
-                                                serverName) != null) {
                     throw new IllegalArgumentException(
                             "Duplicated server name of type " +
                                     serverName.getType());
-                    }
-                }
                 } else {
-                sniNames = Collections.<Integer, SNIServerName>emptyMap();
+                    sniTypes.add(serverName.getType());
+                    sniValues.add(serverName);
                 }
-        } else {
+            }
-            sniNames = null;
+
+            sniNames = Collections.unmodifiableList(sniValues);
         }
     }
 
@@ -388,15 +390,7 @@ public class SSLParameters {
      * @since 1.8
      */
     public final List<SNIServerName> getServerNames() {
-        if (sniNames != null) {
+        return sniNames;
-            if (!sniNames.isEmpty()) {
-                return List.copyOf(sniNames.values());
-            } else {
-                return Collections.<SNIServerName>emptyList();
-            }
-        }
-
-        return null;
     }
 
     /**
@@ -424,22 +418,29 @@ public class SSLParameters {
      * @since 1.8
      */
     public final void setSNIMatchers(Collection<SNIMatcher> matchers) {
-        if (matchers != null) {
+        if (this.sniMatchers == matchers) {
-            if (!matchers.isEmpty()) {
+            return;
-                sniMatchers = new HashMap<>(matchers.size());
+        }
+
+        if (matchers == null) {
+            this.sniMatchers = null;
+        } else if (matchers.isEmpty()) {
+            sniMatchers = Collections.emptyList();
+        } else {
+            List<Integer> matcherTypes = new ArrayList<>(matchers.size());
+            List<SNIMatcher> matcherValues = new ArrayList<>(matchers.size());
             for (SNIMatcher matcher : matchers) {
-                    if (sniMatchers.put(matcher.getType(),
+                if (matcherTypes.contains(matcher.getType())) {
-                                                matcher) != null) {
                     throw new IllegalArgumentException(
                                 "Duplicated server name of type " +
                                 matcher.getType());
-                    }
-                }
                 } else {
-                sniMatchers = Collections.<Integer, SNIMatcher>emptyMap();
+                    matcherTypes.add(matcher.getType());
+                    matcherValues.add(matcher);
                 }
-        } else {
+            }
-            sniMatchers = null;
+
+            this.sniMatchers = Collections.unmodifiableList(matcherValues);
         }
     }
 
@@ -462,15 +463,7 @@ public class SSLParameters {
      * @since 1.8
      */
     public final Collection<SNIMatcher> getSNIMatchers() {
-        if (sniMatchers != null) {
+        return sniMatchers;
-            if (!sniMatchers.isEmpty()) {
-                return List.copyOf(sniMatchers.values());
-            } else {
-                return Collections.<SNIMatcher>emptyList();
-            }
-        }
-
-        return null;
     }
 
     /**