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.SQLMethodInvokeExpr;
  import com.alibaba.druid.sql.ast.expr.SQLValuableExpr;
  import com.alibaba.druid.sql.visitor.SQLEvalVisitor;
  
  import static com.alibaba.druid.sql.visitor.SQLEvalVisitor.EVAL_VALUE;
  
  public class Concat implements Function {
      public static final Concat instance = new Concat();
  
      public Object eval(SQLEvalVisitor visitor, SQLMethodInvokeExpr x) {
          StringBuilder buf = new StringBuilder();
  
          for (SQLExpr item : x.getArguments()) {
              item.accept(visitor);
  
              Object itemValue = item.getAttribute(EVAL_VALUE);
              if (itemValue == null) {
                  return null;
              }
              buf.append(itemValue.toString());
          }
  
          return buf.toString();
      }
  
      public Object eval(SQLMethodInvokeExpr x) {
          StringBuilder buf = new StringBuilder();
          for (SQLExpr param : x.getArguments()) {
              if (param instanceof SQLValuableExpr) {
                  Object val = ((SQLValuableExpr) param).getValue();
                  if (val instanceof String) {
                      buf.append(val);
                      continue;
                  } else if (val instanceof Integer) {
                      buf.append(val);
                      continue;
                  }
              }
  
              return SQLEvalVisitor.EVAL_ERROR;
          }
  
          return buf.toString();
      }
  }
  