利用反射技术将查询结果封装为对象

public class ORMTest extends HttpServlet {

    private static final long serialVersionUID = 1L;


protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {


//创建sql语句


String sql = "select username as Username,password as Password from user where id<?";


//创建个数组，用于给sql语句中的sql赋值


Object obj[] = new Object[]{1020};


try {


//调用getObject方法得到一个Object对象的集合


List<Object> list = getObject(sql, obj, User.class);


//将list存在request域中


request.setAttribute("list", list);


//转发到index.jsp页面


request.getRequestDispatcher("/index.jsp").forward(request, response);


} catch (InstantiationException | IllegalAccessException


| IllegalArgumentException | InvocationTargetException e) {

e.printStackTrace();


}


}


static List<Object> getObject(String sql,Object obj[],Class clazz) throws InstantiationException, IllegalAccessException, IllegalArgumentException, InvocationTargetException{


Connection conn=null;


PreparedStatement ps = null;


ResultSet rs = null;


JDBCUtils utils = JDBCUtils.getInstance();


List<Object> list = new ArrayList<>();


try {


conn = utils.getConnection();


ps = conn.prepareStatement(sql);


//获取参数的元数据


ParameterMetaData pmd = ps.getParameterMetaData();


//获取？个数


int count = pmd.getParameterCount();


//将数组中的元素对应的赋值给sql中的？


for(int i=1;i<=count;i++){


ps.setObject(i, obj[i-1]);


}


//执行sql


rs=ps.executeQuery();


//得到传进来的Bean的所有方法


Method ms[] = clazz.getMethods();


//遍历结果集


while(rs.next()){


//得到结果集元数据


ResultSetMetaData rsmd = rs.getMetaData();


//得到一个结果集的列数


int columnCount = rsmd.getColumnCount();


//得到bean的实例对象


Object object = clazz.newInstance();


//遍历结果集的列


for(int i=1;i<=columnCount;i++){


String columnLabel =rsmd.getColumnLabel(i);//得到列的别名


//得到别名后 可以得到这个列的bean的set方法


String methodName = "set"+columnLabel;


//遍历bean的所有方法


for (Method method : ms) {


//如果有和这个列的set方法相同的方法

if(method.getName().equals(methodName)){


//就将数据库查出来的这个列的值付给这个bean


method.invoke(object, rs.getObject(columnLabel));


}


}


}


//将这个bean添加到集合中

list.add(object);

}

} catch (SQLException e) {


e.printStackTrace();


}finally{


utils.free(conn, ps, rs);


}


return list;


}





}


//bean


public class User {


public User() {





}


public int id;


public String username;


public String password;


public String sex;


public String age;


public int getId() {


return id;


}


public void setId(int id) {


this.id = id;


}


public String getUsername() {


return username;


}


public void setUsername(String username) {


this.username = username;


}


public String getPassword() {


return password;


}


public void setPassword(String password) {


this.password = password;


}


public String getSex() {


return sex;


}


public void setSex(String sex) {


this.sex = sex;


}


public String getAge() {


return age;


}


public void setAge(String age) {


this.age = age;


}


@Override


public String toString() {


return "id="+this.id+"username="+this.username+"password="+this.password


+"age="+this.age+"sex:"+this.sex;


}


}