make visitor null-safe

Author: yuxiqian

flink-cdc-common/src/main/java/org/apache/flink/cdc/common/event/visitor/SchemaChangeEventVisitor.java

@@ -27,60 +27,47 @@
 import org.apache.flink.cdc.common.event.RenameColumnEvent;
 import org.apache.flink.cdc.common.event.SchemaChangeEvent;
 import org.apache.flink.cdc.common.event.TruncateTableEvent;
+import org.apache.flink.cdc.common.utils.Preconditions;
+
+import javax.annotation.Nonnull;
 
 /** Visitor clas for all {@link SchemaChangeEvent}s and returns a specific typed object. */
 @Internal
 public class SchemaChangeEventVisitor {
     public static <T, E extends Throwable> T visit(
             SchemaChangeEvent event,
-            VisitorHandler<AddColumnEvent, T, E> addColumnVisitor,
-            VisitorHandler<AlterColumnTypeEvent, T, E> alterColumnTypeEventVisitor,
-            VisitorHandler<CreateTableEvent, T, E> createTableEventVisitor,
-            VisitorHandler<DropColumnEvent, T, E> dropColumnEventVisitor,
-            VisitorHandler<DropTableEvent, T, E> dropTableEventVisitor,
-            VisitorHandler<RenameColumnEvent, T, E> renameColumnEventVisitor,
-            VisitorHandler<TruncateTableEvent, T, E> truncateTableEventVisitor,
-            VisitorHandler<AlterTableCommentEvent, T, E> alterTableCommentEventVisitor)
+            @Nonnull VisitorHandler<AddColumnEvent, T, E> addColumnVisitor,
+            @Nonnull VisitorHandler<AlterColumnTypeEvent, T, E> alterColumnTypeEventVisitor,
+            @Nonnull VisitorHandler<CreateTableEvent, T, E> createTableEventVisitor,
+            @Nonnull VisitorHandler<DropColumnEvent, T, E> dropColumnEventVisitor,
+            @Nonnull VisitorHandler<DropTableEvent, T, E> dropTableEventVisitor,
+            @Nonnull VisitorHandler<RenameColumnEvent, T, E> renameColumnEventVisitor,
+            @Nonnull VisitorHandler<TruncateTableEvent, T, E> truncateTableEventVisitor,
+            @Nonnull VisitorHandler<AlterTableCommentEvent, T, E> alterTableCommentEventVisitor)
             throws E {
         if (event instanceof AddColumnEvent) {
-            if (addColumnVisitor == null) {
-                return null;
-            }
+            Preconditions.checkNotNull(addColumnVisitor);
             return addColumnVisitor.visit((AddColumnEvent) event);
         } else if (event instanceof AlterColumnTypeEvent) {
-            if (alterColumnTypeEventVisitor == null) {
-                return null;
-            }
+            Preconditions.checkNotNull(alterColumnTypeEventVisitor);
             return alterColumnTypeEventVisitor.visit((AlterColumnTypeEvent) event);
         } else if (event instanceof CreateTableEvent) {
-            if (createTableEventVisitor == null) {
-                return null;
-            }
+            Preconditions.checkNotNull(createTableEventVisitor);
             return createTableEventVisitor.visit((CreateTableEvent) event);
         } else if (event instanceof DropColumnEvent) {
-            if (dropColumnEventVisitor == null) {
-                return null;
-            }
+            Preconditions.checkNotNull(dropColumnEventVisitor);
             return dropColumnEventVisitor.visit((DropColumnEvent) event);
         } else if (event instanceof DropTableEvent) {
-            if (dropTableEventVisitor == null) {
-                return null;
-            }
+            Preconditions.checkNotNull(dropTableEventVisitor);
             return dropTableEventVisitor.visit((DropTableEvent) event);
         } else if (event instanceof RenameColumnEvent) {
-            if (renameColumnEventVisitor == null) {
-                return null;
-            }
+            Preconditions.checkNotNull(renameColumnEventVisitor);
             return renameColumnEventVisitor.visit((RenameColumnEvent) event);
         } else if (event instanceof TruncateTableEvent) {
-            if (truncateTableEventVisitor == null) {
-                return null;
-            }
+            Preconditions.checkNotNull(truncateTableEventVisitor);
             return truncateTableEventVisitor.visit((TruncateTableEvent) event);
         } else if (event instanceof AlterTableCommentEvent) {
-            if (alterTableCommentEventVisitor == null) {
-                return null;
-            }
+            Preconditions.checkNotNull(alterTableCommentEventVisitor);
             return alterTableCommentEventVisitor.visit((AlterTableCommentEvent) event);
         } else {
             throw new IllegalArgumentException(
@@ -90,14 +77,14 @@ public static <T, E extends Throwable> T visit(
 
     public static <E extends Throwable> void voidVisit(
             SchemaChangeEvent event,
-            VoidVisitorHandler<AddColumnEvent, E> addColumnVisitor,
-            VoidVisitorHandler<AlterColumnTypeEvent, E> alterColumnTypeEventVisitor,
-            VoidVisitorHandler<CreateTableEvent, E> createTableEventVisitor,
-            VoidVisitorHandler<DropColumnEvent, E> dropColumnEventVisitor,
-            VoidVisitorHandler<DropTableEvent, E> dropTableEventVisitor,
-            VoidVisitorHandler<RenameColumnEvent, E> renameColumnEventVisitor,
-            VoidVisitorHandler<TruncateTableEvent, E> truncateTableEventVisitor,
-            VoidVisitorHandler<AlterTableCommentEvent, E> alterTableCommentEventHandler)
+            @Nonnull VoidVisitorHandler<AddColumnEvent, E> addColumnVisitor,
+            @Nonnull VoidVisitorHandler<AlterColumnTypeEvent, E> alterColumnTypeEventVisitor,
+            @Nonnull VoidVisitorHandler<CreateTableEvent, E> createTableEventVisitor,
+            @Nonnull VoidVisitorHandler<DropColumnEvent, E> dropColumnEventVisitor,
+            @Nonnull VoidVisitorHandler<DropTableEvent, E> dropTableEventVisitor,
+            @Nonnull VoidVisitorHandler<RenameColumnEvent, E> renameColumnEventVisitor,
+            @Nonnull VoidVisitorHandler<TruncateTableEvent, E> truncateTableEventVisitor,
+            @Nonnull VoidVisitorHandler<AlterTableCommentEvent, E> alterTableCommentEventHandler)
             throws E {
         visit(
                 event,
@@ -113,6 +100,7 @@ public static <E extends Throwable> void voidVisit(
 
     private static <EVT extends SchemaChangeEvent, E extends Throwable>
             VisitorHandler<EVT, Void, E> wrapVoidVisitor(VoidVisitorHandler<EVT, E> handler) {
+        Preconditions.checkNotNull(handler);
         return event -> {
             handler.visit(event);
             return null;