mybatis通用mapper源码解析（一）

1.配置JavaBean与数据库表字段映射关系

/**
 * 字段转换方式
 */
public enum Style {
    normal,                     //原值
    camelhump,                  //驼峰转下划线
    uppercase,                  //转换为大写
    lowercase,                  //转换为小写
    camelhumpAndUppercase,      //驼峰转下划线大写形式
    camelhumpAndLowercase,      //驼峰转下划线小写形式
}

　　根据实体类名称转换表名称

  /**
     * 根据指定的样式进行转换
     *
     * @param str
     * @param style
     * @return
     */
    public static String convertByStyle(String str, Style style) {
        switch (style) {
            case camelhump:
                return camelhumpToUnderline(str);
            case uppercase:
                return str.toUpperCase();
            case lowercase:
                return str.toLowerCase();
            case camelhumpAndLowercase:
                return camelhumpToUnderline(str).toLowerCase();
            case camelhumpAndUppercase:
                return camelhumpToUnderline(str).toUpperCase();
            case normal:
            default:
                return str;
        }

具体的转换方式

  /**
     * 将驼峰风格替换为下划线风格
     */
    public static String camelhumpToUnderline(String str) {
        final int size;
        final char[] chars;
        final StringBuilder sb = new StringBuilder(
                (size = (chars = str.toCharArray()).length) * 3 / 2 + 1);
        char c;
        for (int i = 0; i < size; i++) {
            c = chars[i];
            if (isUppercaseAlpha(c)) {
                sb.append('_').append(toLowerAscii(c));
            } else {
                sb.append(c);
            }
        }
        return sb.charAt(0) == '_' ? sb.substring(1) : sb.toString();
    }

2.通过反射JavaBean拿到所有的field

     /**
         * 获取全部的Field，仅仅通过Field获取
         *
         * @param entityClass
         * @param fieldList
         * @param level
         * @return
         */
        private List<EntityField> _getFields(Class<?> entityClass, List<EntityField> fieldList, Integer level) {
            if (fieldList == null) {
                fieldList = new ArrayList<EntityField>();
            }
            if (level == null) {
                level = 0;
            }
            if (entityClass.equals(Object.class)) {
                return fieldList;
            }
            Field[] fields = entityClass.getDeclaredFields();
            int index = 0;
            for (int i = 0; i < fields.length; i++) {
                Field field = fields[i];
                //排除静态字段，解决bug#2
                if (!Modifier.isStatic(field.getModifiers()) && !Modifier.isTransient(field.getModifiers())) {
                    if (level.intValue() != 0) {
                        //将父类的字段放在前面
                        fieldList.add(index, new EntityField(field, null));
                        index++;
                    } else {
                        fieldList.add(new EntityField(field, null));
                    }
                }
            }
            Class<?> superClass = entityClass.getSuperclass();
            if (superClass != null
                    && !superClass.equals(Object.class)
                    && (superClass.isAnnotationPresent(Entity.class)
                    || (!Map.class.isAssignableFrom(superClass)
                    && !Collection.class.isAssignableFrom(superClass)))) {
                return _getFields(entityClass.getSuperclass(), fieldList, ++level);
            }
            return fieldList;
        }