diff -up ./java/org/apache/jasper/compiler/JDTCompiler.java.orig ./java/org/apache/jasper/compiler/JDTCompiler.java
--- java/org/apache/jasper/compiler/JDTCompiler.java.orig	2021-07-07 11:31:21.583507995 +0800
+++ java/org/apache/jasper/compiler/JDTCompiler.java	2021-07-07 11:35:13.009251246 +0800
@@ -310,7 +310,7 @@ public class JDTCompiler extends org.apa
             } else if(opt.equals("15")) {
                 settings.put(CompilerOptions.OPTION_Source, CompilerOptions.VERSION_15);
             } else if(opt.equals("16")) {
-                settings.put(CompilerOptions.OPTION_Source, CompilerOptions.VERSION_16);
+                settings.put(CompilerOptions.OPTION_Source, "16");
             } else if(opt.equals("17")) {
                 // Constant not available in latest ECJ version shipped with
                 // Tomcat. May be supported in a snapshot build.
@@ -372,8 +372,8 @@ public class JDTCompiler extends org.apa
                 settings.put(CompilerOptions.OPTION_TargetPlatform, CompilerOptions.VERSION_15);
                 settings.put(CompilerOptions.OPTION_Compliance, CompilerOptions.VERSION_15);
             } else if(opt.equals("16")) {
-                settings.put(CompilerOptions.OPTION_TargetPlatform, CompilerOptions.VERSION_16);
-                settings.put(CompilerOptions.OPTION_Compliance, CompilerOptions.VERSION_16);
+                settings.put(CompilerOptions.OPTION_TargetPlatform, "16");
+                settings.put(CompilerOptions.OPTION_Compliance, "16");
             } else if(opt.equals("17")) {
                 // Constant not available in latest ECJ version shipped with
                 // Tomcat. May be supported in a snapshot build.