https://tomcat.apache.org/: Common code shared by multiple Tomcat components 
public final class org.apache.tomcat.util.buf.StringUtils
  minor version: 0
  major version: 59
  flags: flags: (0x0031) ACC_PUBLIC, ACC_FINAL, ACC_SUPER
  this_class: org.apache.tomcat.util.buf.StringUtils
  super_class: java.lang.Object
{
  private static final java.lang.String EMPTY_STRING;
    descriptor: Ljava/lang/String;
    flags: (0x001a) ACC_PRIVATE, ACC_STATIC, ACC_FINAL
    ConstantValue: ""

  private void <init>();
    descriptor: ()V
    flags: (0x0002) ACC_PRIVATE
    Code:
      stack=1, locals=1, args_size=1
        start local 0 // org.apache.tomcat.util.buf.StringUtils this
         0: .line 33
            aload 0 /* this */
            invokespecial java.lang.Object.<init>:()V
         1: .line 35
            return
        end local 0 // org.apache.tomcat.util.buf.StringUtils this
      LocalVariableTable:
        Start  End  Slot  Name  Signature
            0    2     0  this  Lorg/apache/tomcat/util/buf/StringUtils;

  public static java.lang.String join(java.lang.String[]);
    descriptor: ([Ljava/lang/String;)Ljava/lang/String;
    flags: (0x0009) ACC_PUBLIC, ACC_STATIC
    Code:
      stack=1, locals=1, args_size=1
        start local 0 // java.lang.String[] array
         0: .line 39
            aload 0 /* array */
            ifnonnull 2
         1: .line 40
            ldc ""
            areturn
         2: .line 42
      StackMap locals:
      StackMap stack:
            aload 0 /* array */
            invokestatic java.util.Arrays.asList:([Ljava/lang/Object;)Ljava/util/List;
            invokestatic org.apache.tomcat.util.buf.StringUtils.join:(Ljava/util/Collection;)Ljava/lang/String;
            areturn
        end local 0 // java.lang.String[] array
      LocalVariableTable:
        Start  End  Slot   Name  Signature
            0    3     0  array  [Ljava/lang/String;
    MethodParameters:
       Name  Flags
      array  

  public static void join(java.lang.String[], char, java.lang.StringBuilder);
    descriptor: ([Ljava/lang/String;CLjava/lang/StringBuilder;)V
    flags: (0x0009) ACC_PUBLIC, ACC_STATIC
    Code:
      stack=3, locals=3, args_size=3
        start local 0 // java.lang.String[] array
        start local 1 // char separator
        start local 2 // java.lang.StringBuilder sb
         0: .line 47
            aload 0 /* array */
            ifnonnull 2
         1: .line 48
            return
         2: .line 50
      StackMap locals:
      StackMap stack:
            aload 0 /* array */
            invokestatic java.util.Arrays.asList:([Ljava/lang/Object;)Ljava/util/List;
            iload 1 /* separator */
            aload 2 /* sb */
            invokestatic org.apache.tomcat.util.buf.StringUtils.join:(Ljava/lang/Iterable;CLjava/lang/StringBuilder;)V
         3: .line 51
            return
        end local 2 // java.lang.StringBuilder sb
        end local 1 // char separator
        end local 0 // java.lang.String[] array
      LocalVariableTable:
        Start  End  Slot       Name  Signature
            0    4     0      array  [Ljava/lang/String;
            0    4     1  separator  C
            0    4     2         sb  Ljava/lang/StringBuilder;
    MethodParameters:
           Name  Flags
      array      
      separator  
      sb         

  public static java.lang.String join(java.util.Collection<java.lang.String>);
    descriptor: (Ljava/util/Collection;)Ljava/lang/String;
    flags: (0x0009) ACC_PUBLIC, ACC_STATIC
    Code:
      stack=2, locals=1, args_size=1
        start local 0 // java.util.Collection collection
         0: .line 55
            aload 0 /* collection */
            bipush 44
            invokestatic org.apache.tomcat.util.buf.StringUtils.join:(Ljava/util/Collection;C)Ljava/lang/String;
            areturn
        end local 0 // java.util.Collection collection
      LocalVariableTable:
        Start  End  Slot        Name  Signature
            0    1     0  collection  Ljava/util/Collection<Ljava/lang/String;>;
    Signature: (Ljava/util/Collection<Ljava/lang/String;>;)Ljava/lang/String;
    MethodParameters:
            Name  Flags
      collection  

  public static java.lang.String join(java.util.Collection<java.lang.String>, char);
    descriptor: (Ljava/util/Collection;C)Ljava/lang/String;
    flags: (0x0009) ACC_PUBLIC, ACC_STATIC
    Code:
      stack=3, locals=3, args_size=2
        start local 0 // java.util.Collection collection
        start local 1 // char separator
         0: .line 61
            aload 0 /* collection */
            ifnull 1
            aload 0 /* collection */
            invokeinterface java.util.Collection.isEmpty:()Z
            ifeq 2
         1: .line 62
      StackMap locals:
      StackMap stack:
            ldc ""
            areturn
         2: .line 65
      StackMap locals:
      StackMap stack:
            new java.lang.StringBuilder
            dup
            invokespecial java.lang.StringBuilder.<init>:()V
            astore 2 /* result */
        start local 2 // java.lang.StringBuilder result
         3: .line 66
            aload 0 /* collection */
            iload 1 /* separator */
            aload 2 /* result */
            invokestatic org.apache.tomcat.util.buf.StringUtils.join:(Ljava/lang/Iterable;CLjava/lang/StringBuilder;)V
         4: .line 67
            aload 2 /* result */
            invokevirtual java.lang.StringBuilder.toString:()Ljava/lang/String;
            areturn
        end local 2 // java.lang.StringBuilder result
        end local 1 // char separator
        end local 0 // java.util.Collection collection
      LocalVariableTable:
        Start  End  Slot        Name  Signature
            0    5     0  collection  Ljava/util/Collection<Ljava/lang/String;>;
            0    5     1   separator  C
            3    5     2      result  Ljava/lang/StringBuilder;
    Signature: (Ljava/util/Collection<Ljava/lang/String;>;C)Ljava/lang/String;
    MethodParameters:
            Name  Flags
      collection  
      separator   

  public static void join(java.lang.Iterable<java.lang.String>, char, java.lang.StringBuilder);
    descriptor: (Ljava/lang/Iterable;CLjava/lang/StringBuilder;)V
    flags: (0x0009) ACC_PUBLIC, ACC_STATIC
    Code:
      stack=4, locals=3, args_size=3
        start local 0 // java.lang.Iterable iterable
        start local 1 // char separator
        start local 2 // java.lang.StringBuilder sb
         0: .line 72
            aload 0 /* iterable */
            iload 1 /* separator */
            invokedynamic apply()Ljava/util/function/Function;
              Bootstrap: invokestatic java.lang.invoke.LambdaMetafactory.metafactory:(Ljava/lang/invoke/MethodHandles$Lookup;Ljava/lang/String;Ljava/lang/invoke/MethodType;Ljava/lang/invoke/MethodType;Ljava/lang/invoke/MethodHandle;Ljava/lang/invoke/MethodType;)Ljava/lang/invoke/CallSite;
                Method arguments:
                  (Ljava/lang/Object;)Ljava/lang/Object;
                  org/apache/tomcat/util/buf/StringUtils.lambda$0(Ljava/lang/String;)Ljava/lang/String; (6)
                  (Ljava/lang/String;)Ljava/lang/String;
            aload 2 /* sb */
            invokestatic org.apache.tomcat.util.buf.StringUtils.join:(Ljava/lang/Iterable;CLjava/util/function/Function;Ljava/lang/StringBuilder;)V
         1: .line 73
            return
        end local 2 // java.lang.StringBuilder sb
        end local 1 // char separator
        end local 0 // java.lang.Iterable iterable
      LocalVariableTable:
        Start  End  Slot       Name  Signature
            0    2     0   iterable  Ljava/lang/Iterable<Ljava/lang/String;>;
            0    2     1  separator  C
            0    2     2         sb  Ljava/lang/StringBuilder;
    Signature: (Ljava/lang/Iterable<Ljava/lang/String;>;CLjava/lang/StringBuilder;)V
    MethodParameters:
           Name  Flags
      iterable   
      separator  
      sb         

  public static <T> void join(T[], char, java.util.function.Function<T, java.lang.String>, java.lang.StringBuilder);
    descriptor: ([Ljava/lang/Object;CLjava/util/function/Function;Ljava/lang/StringBuilder;)V
    flags: (0x0009) ACC_PUBLIC, ACC_STATIC
    Code:
      stack=4, locals=4, args_size=4
        start local 0 // java.lang.Object[] array
        start local 1 // char separator
        start local 2 // java.util.function.Function function
        start local 3 // java.lang.StringBuilder sb
         0: .line 78
            aload 0 /* array */
            ifnonnull 2
         1: .line 79
            return
         2: .line 81
      StackMap locals:
      StackMap stack:
            aload 0 /* array */
            invokestatic java.util.Arrays.asList:([Ljava/lang/Object;)Ljava/util/List;
            iload 1 /* separator */
            aload 2 /* function */
            aload 3 /* sb */
            invokestatic org.apache.tomcat.util.buf.StringUtils.join:(Ljava/lang/Iterable;CLjava/util/function/Function;Ljava/lang/StringBuilder;)V
         3: .line 82
            return
        end local 3 // java.lang.StringBuilder sb
        end local 2 // java.util.function.Function function
        end local 1 // char separator
        end local 0 // java.lang.Object[] array
      LocalVariableTable:
        Start  End  Slot       Name  Signature
            0    4     0      array  [Ljava/lang/Object;
            0    4     1  separator  C
            0    4     2   function  Ljava/util/function/Function<TT;Ljava/lang/String;>;
            0    4     3         sb  Ljava/lang/StringBuilder;
    Signature: <T:Ljava/lang/Object;>([TT;CLjava/util/function/Function<TT;Ljava/lang/String;>;Ljava/lang/StringBuilder;)V
    MethodParameters:
           Name  Flags
      array      
      separator  
      function   
      sb         

  public static <T> void join(java.lang.Iterable<T>, char, java.util.function.Function<T, java.lang.String>, java.lang.StringBuilder);
    descriptor: (Ljava/lang/Iterable;CLjava/util/function/Function;Ljava/lang/StringBuilder;)V
    flags: (0x0009) ACC_PUBLIC, ACC_STATIC
    Code:
      stack=3, locals=7, args_size=4
        start local 0 // java.lang.Iterable iterable
        start local 1 // char separator
        start local 2 // java.util.function.Function function
        start local 3 // java.lang.StringBuilder sb
         0: .line 87
            aload 0 /* iterable */
            ifnonnull 2
         1: .line 88
            return
         2: .line 90
      StackMap locals:
      StackMap stack:
            iconst_1
            istore 4 /* first */
        start local 4 // boolean first
         3: .line 91
            aload 0 /* iterable */
            invokeinterface java.lang.Iterable.iterator:()Ljava/util/Iterator;
            astore 6
            goto 10
      StackMap locals: java.lang.Iterable int java.util.function.Function java.lang.StringBuilder int top java.util.Iterator
      StackMap stack:
         4: aload 6
            invokeinterface java.util.Iterator.next:()Ljava/lang/Object;
            checkcast java.lang.Object
            astore 5 /* value */
        start local 5 // java.lang.Object value
         5: .line 92
            iload 4 /* first */
            ifeq 8
         6: .line 93
            iconst_0
            istore 4 /* first */
         7: .line 94
            goto 9
         8: .line 95
      StackMap locals: java.lang.Iterable int java.util.function.Function java.lang.StringBuilder int java.lang.Object java.util.Iterator
      StackMap stack:
            aload 3 /* sb */
            iload 1 /* separator */
            invokevirtual java.lang.StringBuilder.append:(C)Ljava/lang/StringBuilder;
            pop
         9: .line 97
      StackMap locals:
      StackMap stack:
            aload 3 /* sb */
            aload 2 /* function */
            aload 5 /* value */
            invokeinterface java.util.function.Function.apply:(Ljava/lang/Object;)Ljava/lang/Object;
            checkcast java.lang.String
            invokevirtual java.lang.StringBuilder.append:(Ljava/lang/String;)Ljava/lang/StringBuilder;
            pop
        end local 5 // java.lang.Object value
        10: .line 91
      StackMap locals: java.lang.Iterable int java.util.function.Function java.lang.StringBuilder int top java.util.Iterator
      StackMap stack:
            aload 6
            invokeinterface java.util.Iterator.hasNext:()Z
            ifne 4
        11: .line 99
            return
        end local 4 // boolean first
        end local 3 // java.lang.StringBuilder sb
        end local 2 // java.util.function.Function function
        end local 1 // char separator
        end local 0 // java.lang.Iterable iterable
      LocalVariableTable:
        Start  End  Slot       Name  Signature
            0   12     0   iterable  Ljava/lang/Iterable<TT;>;
            0   12     1  separator  C
            0   12     2   function  Ljava/util/function/Function<TT;Ljava/lang/String;>;
            0   12     3         sb  Ljava/lang/StringBuilder;
            3   12     4      first  Z
            5   10     5      value  TT;
    Signature: <T:Ljava/lang/Object;>(Ljava/lang/Iterable<TT;>;CLjava/util/function/Function<TT;Ljava/lang/String;>;Ljava/lang/StringBuilder;)V
    MethodParameters:
           Name  Flags
      iterable   
      separator  
      function   
      sb         

  private static java.lang.String lambda$0(java.lang.String);
    descriptor: (Ljava/lang/String;)Ljava/lang/String;
    flags: (0x100a) ACC_PRIVATE, ACC_STATIC, ACC_SYNTHETIC
    Code:
      stack=1, locals=1, args_size=1
        start local 0 // java.lang.String x
         0: .line 72
            aload 0 /* x */
            areturn
        end local 0 // java.lang.String x
      LocalVariableTable:
        Start  End  Slot  Name  Signature
            0    1     0     x  Ljava/lang/String;
}
SourceFile: "StringUtils.java"
InnerClasses:
  public final Lookup = java.lang.invoke.MethodHandles$Lookup of java.lang.invoke.MethodHandles