GUACAMOLE-267: Avoid unnecessarily rebuilding the Guacamole protocol form of a GuacamoleInstruction.

guacamole-common/src/main/java/org/apache/guacamole/protocol/GuacamoleInstruction.java

@@ -33,12 +33,18 @@ public class GuacamoleInstruction {
     /**
      * The opcode of this instruction.
      */
-    private String opcode;
+    private final String opcode;
 
     /**
      * All arguments of this instruction, in order.
      */
-    private List<String> args;
+    private final List<String> args;
+
+    /**
+     * The cached result of converting this GuacamoleInstruction to the format
+     * used by the Guacamole protocol.
+     */
+    private String protocolForm = null;
 
     /**
      * Creates a new GuacamoleInstruction having the given Operation and
@@ -91,12 +97,17 @@ public class GuacamoleInstruction {
      * Returns this GuacamoleInstruction in the form it would be sent over the
      * Guacamole protocol.
      *
-     * @return This GuacamoleInstruction in the form it would be sent over the
+     * @return
+     *     This GuacamoleInstruction in the form it would be sent over the
      *     Guacamole protocol.
      */
     @Override
     public String toString() {
 
+        // Avoid rebuilding Guacamole protocol form of instruction if already
+        // known
+        if (protocolForm == null) {
+
             StringBuilder buff = new StringBuilder();
 
             // Write opcode
@@ -115,7 +126,12 @@ public class GuacamoleInstruction {
             // Write terminator
             buff.append(';');
 
-        return buff.toString();
+            // Cache result for future calls
+            protocolForm = buff.toString();
+
+        }
+
+        return protocolForm;
 
     }