基于JDBC封装的BaseDao(实例代码)

最近闲暇时萌发写一写dao的封装的例子，就将以前写的整理一下。

public class BaseDao<T> {

	Connection conn;
	PreparedStatement st;
	ResultSet rs;

	JdbcUtil jdbcUtil = new JdbcUtil();

	int result = 0;

	private Class<T> persistentClass;

	@SuppressWarnings("unchecked")
	public BaseDaoUtil(){
		conn = jdbcUtil.getConnection();
		ParameterizedType type = (ParameterizedType) getClass().getGenericSuperclass();
		persistentClass = (Class<T>) type.getActualTypeArguments()[0];
	}

  /**
   * 保存
    * @param entity
   * @return
   */
	public int save(T entity) throws Exception{

		String sql = "INSERT INTO "+ entity.getClass().getSimpleName().toLowerCase() +" (";

		List<Method> list = this.matchPojoMethods(entity,"get");

		Iterator<Method> iter = list.iterator();

		Object obj[] = new Object[list.size()];
		int i = 0;
		//拼接字段顺序 insert into table name(id,name,email,
         while(iter.hasNext()) {
            Method method = iter.next();
            sql += method.getName().substring(3).toLowerCase() + ",";
            if (method.getReturnType().getSimpleName().indexOf("Date") !=-1) {
				SimpleDateFormat sbf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
				obj[i] = sbf.format(method.invoke(entity, new Object[]{}));
		   }else {
				obj[i] = method.invoke(entity, new Object[]{});
		   }
      i++;
    }

    //去掉最后一个,符号insert insert into table name(id,name,email) values(
    sql = sql.substring(0, sql.lastIndexOf(",")) + ") values(";

    //拼装预编译SQL语句insert insert into table name(id,name,email) values(?,?,?,
    for(int j = 0; j < list.size(); j++) {
    	sql += "?,";
    }

    //去掉SQL语句最后一个,符号insert insert into table name(id,name,email) values(?,?,?);
    sql = sql.substring(0, sql.lastIndexOf(",")) + ")";

    //到此SQL语句拼接完成,打印SQL语句
    System.out.println(sql);

    try {
    	st = conn.prepareStatement(sql);
    	for (int j = 0; j < obj.length; j++) {
				st.setObject(j+1, obj[j]);
			}
			result = st.executeUpdate();
		} catch (SQLException e) {
			e.printStackTrace();
		}

		jdbcUtil.getClose(rs, st, conn);

		return result;
	}

	/**
	 * 删除
	 * @param object
	 * @return
	 * @throws SQLException
	 */
	public int deleteId(Object object) throws Exception{

		String sql = "delete from "+ persistentClass.getSimpleName().toLowerCase() +" where ";

		//通过子类的构造函数,获得参数化类型的具体类型.比如BaseDAO<T>也就是获得T的具体类型
    T entity = persistentClass.newInstance();

    //存放Pojo(或被操作表)主键的方法对象
    Method idMethod = null;

    List<Method> list = this.matchPojoMethods(entity, "set");
    Iterator<Method> iter = list.iterator();

    //过滤取得Method对象
    while(iter.hasNext()) {
      Method tempMethod = iter.next();
      if(tempMethod.getName().indexOf("Id") != -1 && tempMethod.getName().substring(3).length() == 2) {
        idMethod = tempMethod;
      } else if((entity.getClass().getSimpleName() + "Id").equalsIgnoreCase(tempMethod.getName().substring(3))){
        idMethod = tempMethod;
      }
    }
    //第一个字母转为小写
    sql += idMethod.getName().substring(3,4).toLowerCase()+idMethod.getName().substring(4) + " = ?";

		System.out.println(sql);

		st = conn.prepareStatement(sql);

		//判断id的类型
    if(object instanceof Integer) {
      st.setInt(1, (Integer)object);
    } else if(object instanceof String){
      st.setString(1, (String)object);
    }

		result = st.executeUpdate();

		jdbcUtil.getClose(rs, st, conn);

		return result;
	}

	/**
	 * 修改
	 * @param entity
	 * @return
	 * @throws Exception
	 */
	public int update(T entity) throws Exception{

		String sql = "update "+ entity.getClass().getSimpleName().toLowerCase() +" set ";

		List<Method> list = this.matchPojoMethods(entity, "get");

		//装载参数
		Object obj[] = new Object[list.size()];
		int i = 0;

		//临时Method对象,负责迭代时装method对象.
    Method tempMethod = null;

    //由于修改时不需要修改ID,所以按顺序加参数则应该把Id移到最后.
    Method idMethod = null;
    Iterator<Method> iter = list.iterator();
    while(iter.hasNext()) {
      tempMethod = iter.next();

      //如果方法名中带有ID字符串并且长度为2,则视为ID.
      if(tempMethod.getName().lastIndexOf("Id") != -1 && tempMethod.getName().substring(3).length() == 2) {
      	obj[list.size()-1] = tempMethod.invoke(entity, new Object[]{});
        //把ID字段的对象存放到一个变量中,然后在集合中删掉.
        idMethod = tempMethod;
        iter.remove();
      //如果方法名去掉set/get字符串以后与pojo + "id"想符合(大小写不敏感),则视为ID
      } else if((entity.getClass().getSimpleName() + "Id").equalsIgnoreCase(tempMethod.getName().substring(3))) {
      	obj[list.size()-1] = tempMethod.invoke(entity, new Object[]{});
      	idMethod = tempMethod;
        iter.remove();
      }
    }

    //把迭代指针移到第一位
    iter = list.iterator();
    while(iter.hasNext()) {
      tempMethod = iter.next();
      sql += tempMethod.getName().substring(3).toLowerCase() + "= ?,";
      obj[i] = tempMethod.invoke(entity, new Object[]{});
      i++;
    }

    //去掉最后一个,符号
    sql = sql.substring(0,sql.lastIndexOf(","));

    //添加条件
    sql += " where " + idMethod.getName().substring(3).toLowerCase() + " = ?";

    //SQL拼接完成,打印SQL语句
    System.out.println(sql);

    st = conn.prepareStatement(sql);

    for (int j = 0; j < obj.length; j++) {
			st.setObject(j+1, obj[j]);
		}

    result = st.executeUpdate();

    jdbcUtil.getClose(rs, st, conn);

		return result;

	}

	public T findById(Object object) throws Exception{

		String sql = "select * from "+ persistentClass.getSimpleName().toLowerCase() +" where ";

		//通过子类的构造函数,获得参数化类型的具体类型.比如BaseDAO<T>也就是获得T的具体类型
    T entity = persistentClass.newInstance();

    //存放Pojo(或被操作表)主键的方法对象
    Method idMethod = null;

    List<Method> list = this.matchPojoMethods(entity, "set");
    Iterator<Method> iter = list.iterator();

    //过滤取得Method对象
    while(iter.hasNext()) {
      Method tempMethod = iter.next();
      if(tempMethod.getName().indexOf("Id") != -1 && tempMethod.getName().substring(3).length() == 2) {
        idMethod = tempMethod;
      } else if((entity.getClass().getSimpleName() + "Id").equalsIgnoreCase(tempMethod.getName().substring(3))){
        idMethod = tempMethod;
      }
    }
    //第一个字母转为小写
    sql += idMethod.getName().substring(3,4).toLowerCase()+idMethod.getName().substring(4) + " = ?";

		System.out.println(sql);

		st = conn.prepareStatement(sql);

		//判断id的类型
    if(object instanceof Integer) {
      st.setInt(1, (Integer)object);
    } else if(object instanceof String){
      st.setString(1, (String)object);
    }

    rs = st.executeQuery();

    //把指针指向迭代器第一行
    iter = list.iterator();

    //封装
    while(rs.next()) {
      while(iter.hasNext()) {
        Method method = iter.next();
        if(method.getParameterTypes()[0].getSimpleName().indexOf("String") != -1) {
          //由于list集合中,method对象取出的方法顺序与数据库字段顺序不一致(比如:list的第一个方法是setDate,而数据库按顺序取的是"123"值)
          //所以数据库字段采用名字对应的方式取.
          this.setString(method, entity, rs.getString(method.getName().substring(3).toLowerCase()));
        } else if(method.getParameterTypes()[0].getSimpleName().indexOf("Date") != -1){
          this.setDate(method, entity, rs.getDate(method.getName().substring(3).toLowerCase()));
        }else {
          this.setInt(method, entity, rs.getInt(method.getName().substring(3).toLowerCase()));
        }
      }
    }

    jdbcUtil.getClose(rs, st, conn);

		return entity;

	}

	/**
   * 过滤当前Pojo类所有带传入字符串的Method对象,返回List集合.
   */
  private List<Method> matchPojoMethods(T entity,String methodName) {
    //获得当前Pojo所有方法对象
    Method[] methods = entity.getClass().getDeclaredMethods();

    //List容器存放所有带get字符串的Method对象
    List<Method> list = new ArrayList<Method>();

    //过滤当前Pojo类所有带get字符串的Method对象,存入List容器
    for(int index = 0; index < methods.length; index++) {
      if(methods[index].getName().indexOf(methodName) != -1) {
        list.add(methods[index]);
      }
    }
    return list;
  }

  /**
   * 参数类型为String时,为entity字段设置参数,对应set
   */
  public String setString(Method method, T entity, String arg) throws Exception{
    return (String)method.invoke(entity, new Object[]{arg});
  }

  /**
   * 参数类型为Date时,为entity字段设置参数,对应set
   */
  public Date setDate(Method method, T entity, Date arg) throws Exception{
    return (Date)method.invoke(entity, new Object[]{arg});
  }

  /**
   * 参数类型为Integer或int时,为entity字段设置参数,对应set
   */
  public Integer setInt(Method method, T entity, Integer arg) throws Exception{
    return (Integer)method.invoke(entity, new Object[]{arg});
  }

}

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