需求

将ResultSet中的数据直接封装成实体类。

实现思路

1. 由实体类获取字段数据
2. 由字段数据取对应字段的值
3. 反射创建对象，注入属性值
4. 保留字段数据，以便下次访问

画渣，见谅~

效果展示

测试代码，关键只有中间几行：

@Test
public void fun1() {PreparedStatement ps = null;try {ps = JDBCUtil.getStatement("select id,name,age from student");ResultSet rs = ps.executeQuery();List<Student> list = ResultSetHandler.getList(rs, Student.class);for (Student student : list) {System.out.println(student);}JDBCUtil.commitAndClose(ps);} catch (SQLException throwables) {throwables.printStackTrace();JDBCUtil.rollbackAndClose(ps);}
}

运行效果：

字段数据相关

注解@Row

用以指定列名：

@Target(ElementType.FIELD)
@Retention(RetentionPolicy.RUNTIME)
public @interface Row {String value();
}

属性信息的实体类

用以存放属性的信息：

@Data
public class RowInfo {private final String colName;private final String attrName;private final String attrType;
}

解析一个属性：

private RowInfo(Field field) {Row row = field.getDeclaredAnnotation(Row.class);if (row != null) {this.colName = row.value();this.attrName = field.getName();this.attrType = field.getType().getSimpleName();} else {this.colName = null;this.attrName = null;this.attrType = null;}
}

简单判空：

public Boolean isNull() {return this.colName == null;
}

解析一个实体类：

public static List<RowInfo> createList(Class target) {List<RowInfo> result = new ArrayList<>();for (Field field : target.getDeclaredFields()) {RowInfo info = new RowInfo(field);if (!info.isNull()) {result.add(info);}}return result;
}

从ResultSet中获取该属性的值：

//由ResultSet获取值
public Object getValue(ResultSet resultSet) throws SQLException {switch (attrType) {case "Integer":return resultSet.getInt(colName);case "String":return resultSet.getString(colName);default:return null;}
}

入口

容器，用以存放解析结果，以免每次都要重新解析：

public class ResultSetHandler {private static final ConcurrentHashMap<Class, List<RowInfo>> map = new ConcurrentHashMap();//...
}

获取一个类的解析结果：

private static List<RowInfo> getList(Class target) {List<RowInfo> result = map.get(target);if (result == null) {List<RowInfo> parse = RowInfo.createList(target);map.put(target, parse);return parse;} else {return result;}
}

入口方法：

public static <E> List<E> getList(ResultSet resultSet, Class<E> target) {List<E> result = new ArrayList<>();try {while (resultSet.next()) {E e = create(resultSet, target);result.add(e);}} catch (SQLException e) {e.printStackTrace();}return result;
}

创建实体的方法：

private static <E> E create(ResultSet resultSet, Class<E> target) {E result = null;try {//实例化result = target.newInstance();for (RowInfo info : getList(target)) {Object attr = info.getValue(resultSet);Method method = target.getMethod("set" + upper(info.getAttrName()), attr.getClass());//属性赋值method.invoke(result, attr);}} catch (Exception e) {e.printStackTrace();}return result;
}

杂七杂八：

private static String upper(String name) {return name.substring(0, 1).toUpperCase() + name.substring(1);
}