add mapping support

src/main/java/com/alibaba/druid/sql/SQLUtils.java

@@ -0,0 +1,34 @@
+package com.alibaba.druid.sql;
+
+import com.alibaba.druid.sql.ast.SQLObject;
+import com.alibaba.druid.sql.dialect.mysql.visitor.MySqlOutputVisitor;
+import com.alibaba.druid.sql.dialect.oracle.visitor.OracleOutputVisitor;
+import com.alibaba.druid.sql.dialect.postgresql.visitor.PGOutputVisitor;
+
+public class SQLUtils {
+
+    public static String toMySqlString(SQLObject sqlObject) {
+        StringBuilder out = new StringBuilder();
+        sqlObject.accept(new MySqlOutputVisitor(out));
+
+        String sql = out.toString();
+        return sql;
+    }
+    
+    public static String toOracleString(SQLObject sqlObject) {
+        StringBuilder out = new StringBuilder();
+        sqlObject.accept(new OracleOutputVisitor(out));
+        
+        String sql = out.toString();
+        return sql;
+    }
+    
+    public static String toPGString(SQLObject sqlObject) {
+        StringBuilder out = new StringBuilder();
+        sqlObject.accept(new PGOutputVisitor(out));
+        
+        String sql = out.toString();
+        return sql;
+    }
+ 
+}