KAFKA-19381: add ConfigDef.ConfigKey.Builder

clients/src/main/java/org/apache/kafka/common/config/ConfigDef.java

@@ -21,10 +21,12 @@
 
 import java.util.ArrayList;
 import java.util.Arrays;
+import java.util.Collection;
 import java.util.Collections;
 import java.util.HashMap;
 import java.util.HashSet;
 import java.util.LinkedHashMap;
+import java.util.LinkedHashSet;
 import java.util.LinkedList;
 import java.util.List;
 import java.util.Locale;
@@ -1284,13 +1286,140 @@ private ConfigKey(String name, Type type, Object defaultValue, Validator validat
             this.alternativeString = alternativeString;
         }
 
+        private ConfigKey(ConfigKey.Builder<?> builder) {
+            this(builder.name, builder.type, builder.defaultValue, builder.validator, builder.importance, builder.documentation, builder.group,
+                    builder.orderInGroup, builder.width, builder.displayName, builder.getDependents(), builder.recommender, builder.internalConfig,
+                builder.alternativeString);
+        }
+
+        public static Builder<?> builder(String name) {
+            return new Builder<>(name);
+        }
+
         public boolean hasDefault() {
             return !NO_DEFAULT_VALUE.equals(this.defaultValue);
         }
 
         public Type type() {
             return type;
         }
+
+        public static class Builder<T extends Builder<?>> {
+            private final String name;
+            private ConfigDef.Type type;
+            private Object defaultValue;
+            private ConfigDef.Validator validator;
+            private ConfigDef.Importance importance;
+            private String documentation;
+            private String group;
+            private int orderInGroup;
+            private ConfigDef.Width width;
+            private String displayName;
+            private Set<String> dependents;
+            private ConfigDef.Recommender recommender;
+            private boolean internalConfig;
+            private String alternativeString;
+
+            protected Builder(String name) {
+                this.name = name;
+                this.type = ConfigDef.Type.STRING;
+                this.displayName = name;
+                this.defaultValue = NO_DEFAULT_VALUE;
+                this.orderInGroup = -1;
+                this.width = ConfigDef.Width.NONE;
+            }
+
+            public ConfigDef.ConfigKey build() {
+                return new ConfigKey(this);
+            }
+
+            @SuppressWarnings("unchecked")
+            protected T self() {
+                return (T) this;
+            }
+
+            public final T type(final ConfigDef.Type type) {
+                this.type = type;
+                return self();
+            }
+
+            public final T  defaultValue(final Object defaultValue) {
+                this.defaultValue = defaultValue;
+                return self();
+            }
+
+            public final T validator(final ConfigDef.Validator validator) {
+                this.validator = validator;
+                return self();
+            }
+
+            public final T importance(final ConfigDef.Importance importance) {
+                this.importance = importance;
+                return self();
+            }
+
+            public final T documentation(final String documentation) {
+                this.documentation = documentation;
+                return self();
+            }
+
+            public final T group(final String group) {
+                this.group = group;
+                return self();
+            }
+
+            public final T orderInGroup(final int orderInGroup) {
+                this.orderInGroup = orderInGroup;
+                return self();
+            }
+
+            public final T width(final ConfigDef.Width width) {
+                this.width = width;
+                return self();
+            }
+
+            public final T displayName(final String displayName) {
+                this.displayName = displayName;
+                return self();
+            }
+
+            public final T dependents(final Collection<String> dependents) {
+                if (this.dependents == null) {
+                    this.dependents = new LinkedHashSet<>(dependents);
+                } else {
+                    this.dependents.addAll(dependents);
+                }
+                return self();
+            }
+
+            public final T dependent(final String dependent) {
+                if (this.dependents == null) {
+                    this.dependents = new LinkedHashSet<>();
+                }
+                this.dependents.add(dependent);
+                return self();
+            }
+
+            private List<String> getDependents() {
+                return new LinkedList<>(dependents);
+            }
+
+            public final T recommender(final ConfigDef.Recommender recommender) {
+                this.recommender = recommender;
+                return self();
+            }
+
+            public final T internalConfig(final boolean internalConfig) {
+                this.internalConfig = internalConfig;
+                return self();
+            }
+
+            public final T alternativeString(final String alternativeString) {
+                this.alternativeString = alternativeString;
+                return self();
+            }
+        }
+
     }
 
     protected List<String> headers() {