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比如 电话输入框电话号码的校验，密码规则的校验等 ，我们通常做法是提交操作时对每个输入框的输入内容进行校验，很多的if else ，代码看起来很乱，其实我们可以用反射注解的方式去声明一些判断规则这样会更好，代码可读性更强。

java反射文章推荐：http://www.jianshu.com/p/5b3acad0f025

下面我们通过一个例子去讲解注解方式去实现表达式的校验

这个包下定义的是注解实体类，每一个类都是一个注解规则，如Index类代码：

这个包下都是一些javabean, 如AttrBean代码：

BaseBean基础类，每个bean是一个规则javabean类，

结果回调类

处理回调校验结果

上面主要是校验器和工具类：

public class ValidateUtil {

    /**
     * 设置校验view的信息
     * @param view
     * @param isEditText
     * @param msg
     * @param validateResult
     */
    private static void setViewInfo(Object view, boolean isEditText, String msg, IValidateResult validateResult) {
        if (isEditText) {
            validateResult.onValidateError(msg, ((EditText) view));
        } else {
            validateResult.onValidateError(msg, null);
        }
    }

    /**
     * 不可为空
     * @param view
     * @param isEt
     * @param msg
     * @param validateResult
     * @return
     */
    public static boolean notNull(Object view, boolean isEt, String msg, IValidateResult validateResult) {
        if (TextUtils.isEmpty(((TextView) view).getText().toString())) {
            setViewInfo(view, isEt, msg, validateResult);
            return true;
        }
        return false;
    }

    /**
     * 判断是否为空
     * @param view
     * @return
     */
    public static boolean isNull(Object view) {
        if (view == null)
            throw new NullPointerException("view can not be null");
        if (TextUtils.isEmpty(((TextView) view).getText().toString())) {
            return true;
        }
        return false;
    }

    /**
     * 根据正则表达式校验
     * @param view
     * @param isEt
     * @param bean
     * @param validateResult
     * @return
     */
    public static boolean checkPattern(Object view, boolean isEt, PatternBean bean, IValidateResult validateResult) {
        if (isNull(view)) return true;

        Pattern r = Pattern.compile(bean.pattern);
        Matcher m = r.matcher(((TextView) view).getText().toString());
        if (!m.matches()) {
            setViewInfo(view, isEt, bean.msg, validateResult);
            return true;
        }
        return false;
    }

    /**
     * 最大长度校验
     * @param view
     * @param isEt
     * @param bean
     * @param validateResult
     * @return
     */
    public static boolean maxLenght(Object view, boolean isEt, LengthBean bean, IValidateResult validateResult) {
        if (isNull(view)) return true;

        if (((TextView) view).getText().toString().length() > bean.length) {
            setViewInfo(view, isEt, bean.msg, validateResult);
            return true;
        }
        return false;
    }
}

public class ValidateManager {
    private static final String TAG = "ValidateManager";
    /**
     * 注册的页面
     */
    private static Map<Object, List<AttrBean>> registList = new HashMap<>();
    /**
     * 类型
     */
    private static final String TYPE_NOTNULL = "NotNull";
    private static final String TYPE_PATTERN = "PATTERN";
    private static final String TYPE_MAXLENGTH = "MAXLENGTH";
    private static final String TYPE_MINLENGTH = "MINLENGTH";
    private static final String TYPE_PASSWORDFIRST = "PASSWORD_FIRST";
    private static final String TYPE_PASSWORDSECOND = "PASSWORD_SECOND";
    private static final String TYPE_SKIP = "SKIP";

    public static void check(Object activity, boolean isSkip, IValidateResult validateResult) {
        if (activity == null || validateResult == null) return;
        List<AttrBean> list = registList.get(activity);
        if (list == null) return;
        for (AttrBean attrBean : list) {
            if (attrBean.index == null) {
                return;
            }
        }
        Collections.sort(list, new Comparator<AttrBean>() {
            public int compare(AttrBean arg0, AttrBean arg1) {
                return arg0.index.compareTo(arg1.index);
            }
        });
        for (AttrBean attrBean : list) {
            for (Basebean bean : attrBean.annos) {
                if (isSkip) {
                    if (TYPE_SKIP.equals(attrBean.annos.getLast().type)) {
                        break;
                    }
                }
                if (TYPE_NOTNULL.equals(bean.type)) {
                    if (ValidateUtil.notNull(attrBean.view, attrBean.isEditText, bean.msg, validateResult)) {
                        return;
                    }
                } else if (TYPE_PATTERN.equals(bean.type)) {
                    if (ValidateUtil.checkPattern(attrBean.view, attrBean.isEditText, (PatternBean) bean, validateResult)) {
                        return;
                    }
                } else if (TYPE_MAXLENGTH.equals(bean.type)) {
                    if (ValidateUtil.maxLenght(attrBean.view, attrBean.isEditText, (LengthBean) bean, validateResult)) {
                        return;
                    }
                } else if (TYPE_MINLENGTH.equals(bean.type)) {
                    if (ValidateUtil.minLenght(attrBean.view, attrBean.isEditText, (LengthBean) bean, validateResult)) {
                        return;
                    }
                } else if (TYPE_PASSWORDFIRST.equals(bean.type)) {
                    if (ValidateUtil.isNull(attrBean.view)) {
                        return;
                    }
                    pwd1Attr = attrBean;
                } else if (TYPE_PASSWORDSECOND.equals(bean.type)) {
                    if (ValidateUtil.password(attrBean, pwd1Attr, (PasswordBean) bean, validateResult)) {
                        return;
                    }
                    pwd1Attr = null;
                }
            }
        }
        validateResult.onValidateSuccess();
        pwd1Attr = null;
    }

    private static AttrBean pwd1Attr = null;

    private static class ValidateRegRunnable implements Runnable {
        Object target;

        public ValidateRegRunnable(Object target) {
            this.target = target;
        }

        @Override
        public void run() {
            try {
                Class clazz = target.getClass();

                for (Field field : clazz.getDeclaredFields()) {
                    if (field.isAnnotationPresent(NotNull.class) ||
                            field.isAnnotationPresent(Pattern.class) ||
                            field.isAnnotationPresent(MaxLength.class) ||
                            field.isAnnotationPresent(MinLength.class) ||
                            field.isAnnotationPresent(Index.class) ||
                            field.isAnnotationPresent(PasswordFirst.class) ||
                            field.isAnnotationPresent(PasswordSecond.class)) {

                        if (field.getType() != EditText.class) {
                            throw new RuntimeException("annotation must be on the EditText");
                        }
                        field.setAccessible(true);
                        List<AttrBean> editTextMap = registList.get(target);
                        if (editTextMap == null) {
                            editTextMap = new LinkedList<>();
                            registList.put(target, editTextMap);
                        }
                        AttrBean attr = new AttrBean();
                        attr.name = field.getName();
                        attr.view = field.get(target);

                        if (field.getType() == EditText.class) {
                            attr.isEditText = true;
                        } else if (field.getType() == TextView.class) {
                            attr.isEditText = false;
                        }
                        if (attr.annos == null) {
                            attr.annos = new LinkedList<>();
                        }
                        editTextMap.add(attr);

                        if (field.isAnnotationPresent(NotNull.class))
                            attr.annos.add(validateType(field, TYPE_NOTNULL));
                        if (field.isAnnotationPresent(Pattern.class))
                            attr.annos.add(validateType(field, TYPE_PATTERN));
                        if (field.isAnnotationPresent(MaxLength.class)) {
                            attr.annos.add(validateType(field, TYPE_MAXLENGTH));
                            if (attr.view != null && attr.isEditText) {
                                int length = field.getAnnotation(MaxLength.class).length();
                                ((EditText) attr.view).setFilters(new InputFilter[]{new InputFilter.LengthFilter(length)});
                            }
                        }
                        if (field.isAnnotationPresent(MinLength.class))
                            attr.annos.add(validateType(field, TYPE_MINLENGTH));
                        if (field.isAnnotationPresent(PasswordFirst.class)) {
                            attr.annos.add(validateType(field, TYPE_PASSWORDFIRST));
                            if (attr.view != null && attr.isEditText) {
                                ((EditText) attr.view).setTransformationMethod(PasswordTransformationMethod.getInstance());
                            }
                        }
                        if (field.isAnnotationPresent(PasswordSecond.class)) {
                            attr.annos.add(validateType(field, TYPE_PASSWORDSECOND));
                            if (attr.view != null && attr.isEditText) {
                                ((EditText) attr.view).setTransformationMethod(PasswordTransformationMethod.getInstance());
                            }
                        }
                        if (field.isAnnotationPresent(Index.class))
                            attr.index = field.getAnnotation(Index.class).value();
                        if (field.isAnnotationPresent(Skip.class))
                            attr.annos.add(validateType(field, TYPE_SKIP));
                    }
                }
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
    }

    /**
     * 根据不同类型校验
     * @param field
     * @param type
     * @return
     * @throws IllegalAccessException
     */
    private static Basebean validateType(Field field, String type) throws IllegalAccessException {
        if (type.equals(TYPE_NOTNULL)) {
            NotNull notnull = field.getAnnotation(NotNull.class);
            NotNullBean bean = new NotNullBean();
            bean.msg = notnull.msg();
            bean.type = type;
            return bean;
        } else if (type.equals(TYPE_PATTERN)) {
            Pattern re = field.getAnnotation(Pattern.class);
            PatternBean reBean = new PatternBean();
            reBean.msg = re.msg();
            reBean.type = TYPE_PATTERN;
            reBean.pattern = re.pattern();
            return reBean;
        } else if (type.equals(TYPE_MAXLENGTH)) {
            MaxLength anno = field.getAnnotation(MaxLength.class);
            LengthBean bean = new LengthBean();
            bean.msg = anno.msg();
            bean.type = TYPE_MAXLENGTH;
            bean.length = anno.length();
            return bean;
        } else if (type.equals(TYPE_MINLENGTH)) {
            MinLength anno = field.getAnnotation(MinLength.class);
            LengthBean bean = new LengthBean();
            bean.msg = anno.msg();
            bean.type = TYPE_MINLENGTH;
            bean.length = anno.length();
            return bean;
        } else if (type.equals(TYPE_PASSWORDFIRST)) {
            PasswordBean bean = new PasswordBean();
            bean.type = TYPE_PASSWORDFIRST;
            return bean;
        } else if (type.equals(TYPE_PASSWORDSECOND)) {
            PasswordSecond anno = field.getAnnotation(PasswordSecond.class);
            PasswordBean bean = new PasswordBean();
            bean.msg = anno.msg();
            bean.type = TYPE_PASSWORDSECOND;
            return bean;
        } else if (type.equals(TYPE_SKIP)) {
            Basebean bean = new Basebean();
            bean.type = TYPE_SKIP;
            return bean;
        }

        return null;
    }

    /**
     * 注册
     * @param target
     */
    public static void regist(final Object target) {
        new Thread(new ValidateRegRunnable(target)).start();
    }

    /**
     * 解注册
     * @param target
     */
    public static void unregist(Object target) {
        registList.remove(target);
    }
}

我只贴出了部分代码，可以根据项目实际需求去添加规则，再把相应的校验器代码扩展到这个类里。

我们在主页面使用 按照正常的注解方式去实现 如下：

index是校验的顺序，需要正则表达式校验的输入框我们通过pattern去通过正则表达式去实现，minLength和maxLength是最小最大长度校验

完成后调用ValidateManager.check(this , isSkip , this);实现校验功能，经过回调处理（isSkip是否可以忽略不校验此项）

 可以对指定输入框的view进行错误提醒，比如上面 对输入框背景色设置红色等操作。需源码的留邮箱。