improve wall filter

src/main/java/com/alibaba/druid/sql/parser/Lexer.java

@@ -68,10 +68,20 @@ public class Lexer {
 
     private int            varIndex     = -1;
 
+    protected CommentHandler commentHandler;
+
     public Lexer(String input){
         this(input, true);
     }
 
+    public CommentHandler getCommentHandler() {
+        return commentHandler;
+    }
+
+    public void setCommentHandler(CommentHandler commentHandler) {
+        this.commentHandler = commentHandler;
+    }
+
     public final char charAt(int index) {
         if (index >= text.length()) {
             return EOI;
@@ -1008,4 +1018,9 @@ public class Lexer {
     public BigDecimal decimalValue() {
         return new BigDecimal(text.toCharArray(), mark, bufPos);
     }
+
+    public static interface CommentHandler {
+
+        boolean handle(Token lastToken, String comment);
+    }
 }

src/main/java/com/alibaba/druid/sql/parser/NotAllowCommentException.java

@@ -20,7 +20,7 @@ public class NotAllowCommentException extends ParserException {
     private static final long serialVersionUID = 1L;
 
     public NotAllowCommentException(){
-        super();
+        this("comment not allow");
     }
 
     public NotAllowCommentException(String message, Throwable e){

src/main/java/com/alibaba/druid/sql/parser/SQLSelectParser.java

@@ -141,6 +141,10 @@ public class SQLSelectParser extends SQLParser {
         }
 
         accept(Token.SELECT);
+        
+        if (lexer.token() == Token.COMMENT) {
+            lexer.nextToken();
+        }
 
         SQLSelectQueryBlock queryBlock = new SQLSelectQueryBlock();
 

src/main/java/com/alibaba/druid/sql/parser/SQLStatementParser.java

@@ -617,6 +617,10 @@ public class SQLStatementParser extends SQLParser {
             if (lexer.token() == (Token.FROM)) {
                 lexer.nextToken();
             }
+            
+            if (lexer.token() == Token.COMMENT) {
+                lexer.nextToken();
+            }
 
             SQLName tableName = exprParser.name();