content: /*
   * Copyright 1999-2017 Alibaba Group Holding Ltd.
   *
   * Licensed under the Apache License, Version 2.0 (the "License");
   * you may not use this file except in compliance with the License.
   * You may obtain a copy of the License at
   *
   *      http://www.apache.org/licenses/LICENSE-2.0
   *
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS,
   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   * See the License for the specific language governing permissions and
   * limitations under the License.
   */
  package com.alibaba.druid.sql.visitor.functions;
  
  import com.alibaba.druid.sql.ast.SQLExpr;
  import com.alibaba.druid.sql.ast.expr.SQLCharExpr;
  import com.alibaba.druid.sql.ast.expr.SQLMethodInvokeExpr;
  import com.alibaba.druid.sql.visitor.SQLEvalVisitor;
  
  import java.text.ParseException;
  import java.text.SimpleDateFormat;
  import java.util.List;
  
  import static com.alibaba.druid.sql.visitor.SQLEvalVisitor.EVAL_ERROR;
  
  public class ToDate implements Function {
      public static final ToDate instance = new ToDate();
  
      public Object eval(SQLEvalVisitor visitor, SQLMethodInvokeExpr x) {
          final List<SQLExpr> arguments = x.getArguments();
          if (arguments.isEmpty()) {
              return EVAL_ERROR;
          }
  
          if (arguments.size() == 2
                  && arguments.get(0) instanceof SQLCharExpr
                  && arguments.get(1) instanceof SQLCharExpr) {
              String chars = ((SQLCharExpr) arguments.get(0)).getText();
              String format = ((SQLCharExpr) arguments.get(1)).getText();
              if (format.equals("yyyymmdd")) {
                  SimpleDateFormat dateFormat = new SimpleDateFormat("yyyyMMdd");
                  try {
                      return dateFormat.parse(chars);
                  } catch (ParseException e) {
                      // skip
                      return false;
                  }
              }
          }
  
          return null;
      }
  }
  