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);
       }

    }

    }