# Concepts

## Input

input is the object to be validated, it is the first parameter of the `val` function.

`RebbVal` support following datatypes:

### Datatype in input

#### Boolean

#### Number

Include integer, long, float, double, all input numbers will be casted to BigDecimal(in Java implementation).

#### Date

In Java implementation，the input could been a `java.uitl.Date`

{% hint style="info" %}
`RebbVal`has a function`date()`to parse `string` to `Date`
{% endhint %}

```java
RebbVal v = new RebbVal();
v.val(v.date("2010-05-01"),"between 2010-01-01 and 2020-01-01"); // true 

// custom pattern for parser
v.val(v.date("2020/12/31","yyyy/MM/dd"), "[2020-01-01, 2021-12-31]"); //true
```

{% hint style="info" %}
`RebbVal`has a function`year()`to convert `string` to `Date`
{% endhint %}

```java
v.val(v.year("2000"), "is leapyear"); //true
```

#### String

## Rule

Rule is the second parameter of the`val` function

A rule is just a string, the supported rule grammar are:

* comparions: =, !=, >,<,>=,<=
* between .. and ..
* interval
* in (array)
* contains
* not empty
* max length
* is (true, false, phone, email, ipv4,url, ect.)
* is (custom function)
* match (regex)
* older than/younger than
* starts with/ends with

Rules can be negated by using `not` operation

Rules can be combined with `and`, `or`

### Datatype in rule

#### array

```java
// array of numbers
[1,2,3.0]

// array of strings
['foo','bar']
```

#### boolean

```java
true

false
```

#### number

```java
// integer
1
-300
// float
3.1415
-39.

// not supported yet
// .8
// 80%
// 1.05e8
```

#### date

```java
// yyyy-MM-dd
2014-12-01

// without leading zeros
2020-1-1
```

#### regex

```java
// the delimiter is slash
/^\d+$/

//modifier support：g,i,m,s,x,u,U
/\d+/g

```

#### string

```java
// using single quotes
'a string'
```

## Result

The result of the `val` function is a boolean.

If result is true, means all rules are satisfied, if false, you can check errors by calling `getErrors` function

## Error

If the result of `val` is false, or `hasError` function returns `true`, then the validataion failed.

You can call `getErrors` function, which returns an array of string(in Java, an ArrayList\<String>), to get the detail message.

```java
v.val(8.8,">=10"); // false
v.getErrors().size() // 1
v.getErrors().get(0) // 8.8 >=10 failed
```

## Custom Validator

Write a class that implements `com.rebb.val.IValidator` interface

```java
package com.rebb.valid;

public interface IValidator {
    public boolean run(Object obj) throws ValidationException;
}
```

In the run function, do your validate work and return a boolean as validation result.

```java
package com.example.valid;

public class DemoCustomValidator implements IValidator{

    @Override
    public boolean run(Object obj) throws ValidationException {
        if(obj instanceof String)
        {
            String object = (String)obj;
            return object.equals("Demo");
        }
        else
        {
            throw new ValidationException("Unsupported object type");
        }
    }
}

```

After initialize the `RebbVal` object, call `registerCustomValidator` function

```java
Valid v = new Valid();
v.registerCustomValidator("Demo", DemoCustomValidator.class);
v.val("Demo","is Demo"); // true
```

## Timezone

When we deal with date, timezone is always the first consideration, you can set the timezone like this:

```java
Valid v = new Valid();
v.setTimezone(Locale.CHINA);
```


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