Java map 常用方法
Map的一般用法
1.声明一个Map :
Map map = new HashMap();
2 .向map中放值 ,注意: map是key-value的形式存放的,如:
map.put("sa","dd");
3 .从map中取值 :
String str = map.get("sa").toString,
结果是: str = "dd'
4 .遍历一个map,从中取得key和value :
Map m= new HashMap();
for(Object obj : map.keySet()){
Object value = map.get(obj );
}
通过sql获得map集合
public HashMap<String, String> getMapBySql(String sql, Object params[],
String keyColName, String valueColName)
{
HashMap<String, String> strMap = new HashMap<String, String>();
try
{
List<HashMap<String, Object>> resultList = query(sql, params);
if (resultList != null && resultList.size() > 0)
{
for (HashMap<String, Object> resultMap : resultList)
{
if (resultMap != null && resultMap.size() > 0)
{
String key = GetValueFromHashMap
.getStringValueByColumnName(resultMap, keyColName);
String value = GetValueFromHashMap
.getStringValueByColumnName(resultMap, valueColName);
strMap.put(key, value);
}
}
}
}
catch (Exception e)
{
System.out.println("sql出现异常:" + e.toString() + " sql=" + sql);
}
return strMap;
}
public static String getStringValueByColumnName(HashMap<String,Object> map,String colName)
{
return getStringValueByColumnName(map,colName,"");
}
public static String getStringValueByColumnName(HashMap<String,Object> map,String colName,String defaultValue)
{
String value=defaultValue;
if(map!=null&&map.size()>0&&colName!=null&&colName.length()>0)
{
if(map.get(colName)!=null&&map.get(colName).toString().length()>0)
{
value=map.get(colName).toString();
}
}
return value;
}