//查询多条记录，返回对应的对象的集合 public List getForList(Class clazz, String sql, Object...args){

List list = new ArrayList();

Connection connection = null;

PreparedStatement preparedStatement = null;

ResultSet resultSet = null;

try {

//1.得到结果集   connection = JDBCTools.GetConnection();

preparedStatement = connection.prepareStatement(sql);

for(int i = 0; i < args.length; i++){

preparedStatement.setObject(i + 1, args[i]);

}

resultSet = preparedStatement.executeQuery();

//2.处理结果集，得到 Map 的List，其中 一个 Map对象 就是一条记录

//Map 的 key 为 resultSet 中 列的别名， Map的 value 为列的值   List> values = handleResultSettoMapList(resultSet);

//3.把 Map的List 转为 clazz 对应的 List

//其中 Map 的key 即为 clazz 对应的对象的 propertyName

//而 Map 的 value 即为 clazz 对应的对象的 propertyValue。   list = transferMapListToBeanList(clazz, values);

} catch (Exception e) {

e.printStackTrace();

}finally{

JDBCTools.release(resultSet, preparedStatement, connection);

}

return list;

}

/**

* 处理结果集，得到 Map的一个List，其中 一个 Map对象对应一条记录

*@paramresultSet

*@return

*@throwsSQLException

*/ private List> handleResultSettoMapList(

ResultSet resultSet) throws SQLException {

//5.准备一个 List>:

//键：存放列的别名， 值：存放列的值。其中一个Map 对象对应着一条记录  List> values =

new ArrayList>();

ResultSetMetaData rsmd = resultSet.getMetaData();

Map map = null;

//7.处理 ResultSet， 使用 while 循环  while(resultSet.next()){

map = new HashMap();

for(int i = 0; i < rsmd.getColumnCount(); i ++){

String columLabel = rsmd.getColumnLabel(i + 1);

Object value = resultSet.getObject(i + 1);

map.put(columLabel, value);

}

//11.把一条记录的一个 Map 对象放入 5 准备的List中   values.add(map);

}

return values;

}

private List transferMapListToBeanList(Class clazz,

List> values) throws InstantiationException,

IllegalAccessException, InvocationTargetException {

//12. 判断 List 是否为空集合，若不为空

//则遍历List，得到一个一个的Map对象，再把一个 Map对象转换为一个 Class参数对应的 Object对象  List result = new ArrayList();

T bean = null;

if(values.size() > 0){

for(Map m:values){

bean = clazz.newInstance();

for(Map.Entry entry:m.entrySet()){

String propertyName = entry.getKey();

Object value = entry.getValue();

BeanUtils.setProperty(bean, propertyName, value);

}

//13. 把 Object 对象放入到 list 中    result.add(bean);

}

}

return result;

}

//查询一条记录，返回对应的对象 public T get(Class clazz, String sql, Object...args){

List results = getForList(clazz, sql, args);

if(results.size() > 0){

return results.get(0);

}

return null;

}

//返回某条记录的某一个字段的值 或一个统计的值(一共有多少条记录等) public E getForValue(String sql, Object...args){

//1.得到结果集：该结果集应该只有一行，且只有一列  Connection connection = null;

PreparedStatement preparedStatement = null;

ResultSet resultSet = null;

try {

//1.得到结果集   connection = JDBCTools.GetConnection();

preparedStatement = connection.prepareStatement(sql);

for(int i = 0; i < args.length; i++){

preparedStatement.setObject(i + 1, args[i]);

}

resultSet = preparedStatement.executeQuery();

//2.取得结果集   if(resultSet.next()){

return (E) resultSet.getObject(1);

}

} catch(Exception e){

e.printStackTrace();

} finally{

JDBCTools.release(resultSet, preparedStatement, connection);

}

return null;

}

测试

@Test

public void testGet() {

String sql = "SELECT flow_id flowid, type, id_card idcard," +

" exam_card examcard,"

+ "student_name studentname, location, grade " + "FROM examstudent "

+ "WHERE flow_id = ?";

Student student = dao.get(Student.class, sql, 7);

System.out.println(student);

}

@Test

public void testGetForList() {

String sql = "SELECT flow_id flowid, type, id_card idcard," +

" exam_card examcard,"

+ "student_name studentname, location, grade " + "FROM examstudent";

List students = dao.getForList(Student.class, sql);

System.out.println(students);

}

@Test

public void testGetForValue() {

String sql = "SELECT id_card idcard FROM examstudent "

+ "WHERE flow_id = ?";

String idCard = dao.getForValue(sql, 7);

System.out.println(idCard);

sql = "SELECT max(grade) FROM examstudent";

int grade = dao.getForValue(sql);

System.out.println(grade);

}