使用反射实现ORM

首先Bean在符合JavaBean的要求,即有一个无参的构造方法,所有属性都有一个set和get方法并且set与get方法是set/get+属性名称(属性名称先字母大写)

public class User {

    private int id;

 

    private String name;

 

    private Date birthday;

 

    private float money;

 

    public User() {

 

    }

 

    public Date getBirthday() {

       return birthday;

    }

 

    public void setBirthday(Date birthday) {

       this.birthday = birthday;

    }

 

    public int getId() {

       return id;

    }

 

    public void setId(int id) {

       this.id = id;

    }

 

    public float getMoney() {

       return money;

    }

 

    public void setMoney(float money) {

       this.money = money;

    }

 

    public String getName() {

       return name;

    }

 

    public void setName(String name) {

       this.name = name;

    }

 

}

 

 

public class ORMTest {

 

    public static void main(String[] args) throws SQLException,

           IllegalAccessException, InvocationTargetException, Exception {

       User user = (User) getObject(

              "select id as Id, name as Name, birthday as Birthday, money as Money  from user where id=1",

              User.class);

       //这里取别名就是为了便列名加set或get就可以是JavaBean中属性的set或get方法

       System.out.println(user);

 

       Bean b = (Bean) getObject(

              "select id as Id, name as Name, birthday as Birthday, money as Money from user where id=1",

              Bean.class);

       System.out.println(b);

    }

   

    private static String[] getColNames(ResultSet rs) throws SQLException {

       ResultSetMetaData rsmd = rs.getMetaData();

       int count = rsmd.getColumnCount();

       String[] colNames = new String[count];

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

           colNames[i - 1] = rsmd.getColumnLabel(i);

       }

       return colNames;

    }

 

    static Object getObject(String sql, Class clazz) throws SQLException,

           Exception, IllegalAccessException, InvocationTargetException {

       Connection conn = null;

       PreparedStatement ps = null;

       ResultSet rs = null;

       try {

           conn = JdbcUtils.getConnection();

           ps = conn.prepareStatement(sql);

           rs = ps.executeQuery();

           String[] colNames = getColNames(rs);//得到所有的列名

 

           Object object = null;

           Method[] ms = clazz.getMethods();//得到javaBean中所有set或get方法

           if (rs.next()) {

              object = clazz.newInstance();

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

                  String colName = colNames[i];

                  String methodName = "set" + colName;//得到set或get方法名

                  for (Method m : ms) {

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

                         m.invoke(object, rs.getObject(colName));//调用set方法,将该列的值放到set方法当中去.

                         break;

                     }

                  }

              }

           }

           return object;

       } finally {

           JdbcUtils.free(rs, ps, conn);

       }

    }

    }

评论

1 楼 tiantianfei 2009-04-24  

hibernate实现的方法,和你所列出来的,原理是一样的么?