java使用Field实现通用数据库操作

上次介绍了Field，可以其可以在运行时候获取类中的信息，这是个好东西，我们可以用它来实现数据库的增删改查操作

当然，需要有一些限制：

1.表和实体类字段要对应

2.表和实体类名字要对应

3.实体类的第一个字段必须是主键(这个主要在更新的时候用到，具体根据个人情况而定)

数据库操作类如下

public class ReflectDao {
	private static String uri = "jdbc:mysql://localhost/reflect";
	private static String password = "123";
	private static String username = "xhe";
	private String insert = "insert into ";
	private String update = "update ";
	private String delete = "delete from ";
	private String select = "select * from ";

	public Connection getConnection() {
		try {
			Class.forName("com.mysql.jdbc.Driver");
			Connection conn = DriverManager.getConnection(uri, username, password);
			return conn;
		} catch (Exception e) {
			e.printStackTrace();
		}
		return null;
	}

	public void save(Object obj, Class clazz) {
		Connection conn = null;
		Statement s = null;
		try {
			Field[] fields = clazz.getDeclaredFields();

			insert += clazz.getSimpleName() + " values(";

			for (int i = 0; i < fields.length; i++) {
				fields[i].setAccessible(true);
				if (fields[i].get(obj) != null) {
					if (i == 0) {
						insert = insert + "'" + fields[i].get(obj) + "'";
					} else {
						insert = insert + ",'" + fields[i].get(obj) + "'";
					}

				} else {
					if (i == 0) {
						insert = insert + "" + fields[i].get(obj) + "";
					} else {
						insert = insert + "," + fields[i].get(obj) + "";
					}
				}
			}
			insert += ")";
			System.out.println(insert);

			conn = getConnection();
			s = conn.createStatement();
			s.execute(insert);

		} catch (Exception e) {
			e.printStackTrace();
		} finally {
			try {
				if (s != null)
					s.close();
				if (conn != null)
					conn.close();
			} catch (Exception e) {
				e.printStackTrace();
			}
		}
	}

	public void update(Object obj, Class clazz) {
		Connection conn = null;
		Statement s = null;
		try {
			Field[] fields = clazz.getDeclaredFields();

			update += clazz.getSimpleName() + " set ";

			for (int i = 0; i < fields.length; i++) {
				fields[i].setAccessible(true);
				if (fields[i].get(obj) != null) {
					if (i == 0) {
						update = update + fields[i].getName() + " = '" + fields[i].get(obj) + "'";
					} else {
						update = update + "," + fields[i].getName() + " = '" + fields[i].get(obj) + "'";
					}

				}
			}
			update += " where " + fields[0].getName() + " = " + fields[0].get(obj);

			System.out.println(update);

			conn = getConnection();
			s = conn.createStatement();
			s.executeUpdate(update);

		} catch (Exception e) {
			e.printStackTrace();
		} finally {
			try {
				if (s != null)
					s.close();
				if (conn != null)
					conn.close();
			} catch (Exception e) {
				e.printStackTrace();
			}
		}
	}

	public List find(Object obj, Class clazz) {
		Connection conn = null;
		Statement s = null;
		ResultSet rs = null;
		List list = new ArrayList();

		try {
			Field[] fields = clazz.getDeclaredFields();

			select += clazz.getSimpleName() + " where 1 = 1";

			for (int i = 0, length = fields.length; i < length; i++) {
				fields[i].setAccessible(true);
				if (fields[i].get(obj) != null) {
					select = select + " and " + fields[i].getName() + " = '" + fields[i].get(obj) + "'";
				}
			}
			System.out.println(select);

			conn = getConnection();
			s = conn.createStatement();
			rs = s.executeQuery(select);

			while (rs.next()) {
				Object o = clazz.newInstance();
				for (int i = 0, length = fields.length; i < length; i++) {
					fields[i].setAccessible(true);
					fields[i].set(o, rs.getObject(i + 1));
				}
				list.add(o);
			}

		} catch (Exception e) {
			e.printStackTrace();
		} finally {
			try {
				if (s != null)
					s.close();
				if (conn != null)
					conn.close();
			} catch (Exception e) {
				e.printStackTrace();
			}
		}
		return list;
	}

	public void delete(Object obj, Class clazz) {
		Connection conn = null;
		Statement s = null;
		ResultSet rs = null;

		try {
			Field[] fields = clazz.getDeclaredFields();

			delete += clazz.getSimpleName() + " where 1 = 1";

			for (int i = 0, length = fields.length; i < length; i++) {
				fields[i].setAccessible(true);
				if (fields[i].get(obj) != null) {
					delete = delete + " and " + fields[i].getName() + " = '" + fields[i].get(obj) + "'";
				}
			}
			System.out.println(delete);

			conn = getConnection();
			s = conn.createStatement();
			s.executeUpdate(delete);

		} catch (Exception e) {
			e.printStackTrace();
		} finally {
			try {
				if (s != null)
					s.close();
				if (conn != null)
					conn.close();
			} catch (Exception e) {
				e.printStackTrace();
			}
		}
	}
}

这个类很简单，外部调用的时候只需要传入对应的对象和class对象，就可以进行增删改查操作

测试类如下

	public static void main(String[] args) {
		ReflectDao reflect = new ReflectDao();
		Student s = new Student();
		s.setAge(12);
		s.setName("tom");
		s.setSex("man");
		s.setStudentid(1130299110);
		reflect.save(s, s.getClass());
	}

这样就可以把Student的信息保存到数据库的Student表了(表就4个字段)

不得不说Field是一个好东西，不过这里主要是大概的提供一种应用，所以上面的程序会有BUG或者不完美的地方，各位可以使用Field去写一个自己的操作方法