开发中遇到问题

今天在生产中遇到了并发导致数据null的问题：

代码：

 public static String getAddressName(String type, String code) {
      /*String strReturn = "";
         ExeSQL exeSql = new ExeSQL();
         String sql = "select placeName from ldaddress where placeType='" + type
                 + "' and placeCode='" + code + "'";
         strReturn = exeSql.getOneValue(sql);
         return strReturn;*/
//     缓存减少查询次数
      if(addressName == null || !addressName.containsKey( type + "_" + code )){
       addressName = new HashMap<String, String>();
       String sql = "select placeType,placeCode,placeName from ldaddress";
       ExeSQL exesql = new ExeSQL();
       SSRS ssrs = exesql.execSQL(sql);
       String key = null;
       String value = null;
       for (int i = 1; i <= ssrs.getMaxRow(); i++) {
    key = ssrs.GetText(i, 1) + "_" + ssrs.GetText(i, 2);
    value = ssrs.GetText(i, 3);
    addressName.put(key, value);
   }
      }
      return addressName.get( type + "_" + code );
//  end
    }

问题解决：

public static String getAddressName(String type, String code) {
  /*
   * String strReturn = ""; ExeSQL exeSql = new ExeSQL(); String sql =
   * "select placeName from ldaddress where placeType='" + type +
   * "' and placeCode='" + code + "'"; strReturn =
   * exeSql.getOneValue(sql); return strReturn;
   */
  // start  缓存减少查询次数
  synchronized (addressName) {
   if (!addressName.containsKey(type + "_" + code)) {
    String sql = "select placeType,placeCode,placeName from ldaddress";
    ExeSQL exesql = new ExeSQL();
    SSRS ssrs = exesql.execSQL(sql);
    String key = null;
    String value = null;
    for (int i = 1; i <= ssrs.getMaxRow(); i++) {
     key = ssrs.GetText(i, 1) + "_" + ssrs.GetText(i, 2);
     value = ssrs.GetText(i, 3);
     addressName.put(key, value);
    }
   }
  }
  return addressName.get(type + "_" + code);
  // end
 }