java用反射实现动态RowMapper

jdbcTemplate查询返回对象的时候，可以自定义rowmapper,也有一个BeanPropertyRowMapper可以用，但要求类属性和表字段严格对应；

如果我们的表字段跟类不能严格对应，这个时候只能写RowMapper,但又不想一个一个写，怎么办？

我们可以通过反射，来动态实现RowMapper

大家可以看到我这个model类，属性和表里的字段是无法映射的，这个时候BeanPropertyRowMapper排不上用场。

只能自定义了

@Table(name = "table_name")
public class TableClass implements Serializable {
    private static final long serialVersionUID = -7355355251303268193L;

    
    @Column(name="bizmonth")
    private String bizMonth;

    
    @Column(name="complete_num_1m")
    private Long completeNum;

    
    @Column(name="uncomplete_num_1m")
    private Long unCompleteNum;

    
    @Column(name="total_num_1m")
    private Long totalNum;

}

反射获取RowMapper

/**
     * 查询表column对应的类field
     * @param clazz
     * @return
     */
    public static Map<String, Field> getColumnMap(Class<?> clazz) {
        Map<String, Field> map = new HashMap<>();
        Field[] declaredFields = clazz.getDeclaredFields();
        for (Field declaredField : declaredFields) {
            String fieldName = declaredField.getName();
            if (!fieldName.equals("serialVersionUID")) {
                if (declaredField.isAnnotationPresent(Column.class)) {
                    Column fieldAnnotation = declaredField.getAnnotation(Column.class);
                    String columnName = fieldAnnotation.name();
                    map.put(columnName, declaredField);
                } else {
                    throw new NullPointerException("字段缺少Column注解");
                }

            }
        }
        return map;
    }

/**
* 获取一个类的RowMapper
*/
public static <T> RowMapper<T> getRowMapper(Class<T> clazz) {
        Map<String, Field> columnMap = getColumnMap(clazz);
        RowMapper<T> rowMapper = new RowMapper<T>() {
            @Override
            public T mapRow(ResultSet rs, int i) throws SQLException {
                try {
                    T t = clazz.newInstance();
                    for (Map.Entry<String, Field> entry : columnMap.entrySet()) {
                        String columnName = entry.getKey();
                        Field field = entry.getValue();
                        field.setAccessible(true);
                        Object columnVal = rs.getObject(columnName);
                        field.set(t, columnVal);
                    }
                    return t;
                } catch (InstantiationException | IllegalAccessException e) {
                    e.printStackTrace();
                }
                return null;
            }
        };
        return rowMapper;
    }

大功告成！