利用反射技术将查询结果封装为对象

来源：互联网发布：源码社区uuv9 编辑：程序博客网时间：2024/04/30 01:03
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;    }}//beanpublic 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;    }}
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