Validator Interface in Spring
July 12, 2022
Validator interface.
1. The
Validator interface is a validator for application-specific objects.
2. The
Validator interface can be used in web tier, the data-access tier, or the whatever-tier.
3. It can be used in any layer of an application, and supports the encapsulation of validation logic.
4. It is useful for custom validation in our Spring application.
5. The
Validator interface has following method declarations.
a.
boolean supports(Class<?> clazz)
Validator can validate instances of the supplied clazz?
Parameters:
The clazz is the class that this
Validator is being asked if it can validate.
Returns:
true if this
Validator can validate instances of the supplied clazz.
b.
void validate(Object target, Errors errors)
Parameters:
The target is the object that is to be validated.
The errors is the contextual state about the validation process.
Maven Dependency
pom.xml
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter</artifactId>
<version>1.2.7.RELEASE</version>
</dependency>
Create Custom Validator implementing Validator Interface
To useValidator interface, we need to create a custom validator class implementing Validator interface.
Find our custom validator class.
UserValidator.java
package com.concretepage.validator;
import java.io.IOException;
import java.util.Properties;
import org.springframework.beans.factory.annotation.Required;
import org.springframework.core.io.Resource;
import org.springframework.core.io.support.PropertiesLoaderUtils;
import org.springframework.validation.Errors;
import org.springframework.validation.ValidationUtils;
import org.springframework.validation.Validator;
import com.concretepage.bean.User;
public class UserValidator implements Validator {
private Resource location;
@Required
public void setLocation(Resource location) {
this.location = location;
}
@Override
public boolean supports(Class cls) {
return User.class.equals(cls);
}
@Override
public void validate(Object ob, Errors err) {
Properties props=null;
try {
props = PropertiesLoaderUtils.loadProperties(location);
} catch (IOException e) {
e.printStackTrace();
}
String msg1 = props.getProperty("errormsg.name");
ValidationUtils.rejectIfEmpty(err, "name", "errormsg.name",msg1);
User user = (User)ob;
if(user.getAge()<18){
String msg2 = props.getProperty("errormsg.age");
err.rejectValue("age","errormsg.age",msg2);
}
}
}
java.util.Properties.
ValidationUtils : A Utility class that has methods to invoke validator.
Errors : Keeps the error message and exposes the data-binding for any object.
Now find the
User class used in demo.
User.java
package com.concretepage.bean;
public class User {
private String name;
private int age;
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}
}
Message Property File
messages_en.propertieserrormsg.name = Name can not be blank. errormsg.age = The age entered is not valid.
Create Bean for Validator
spring-app.xml
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.springframework.org/schema/beans
http://www.springframework.org/schema/beans/spring-beans-3.0.xsd ">
<bean id="user" class="com.concretepage.bean.User">
<property name="name" value=""/>
<property name="age" value="16"/>
</bean>
<bean id="userValidator" class="com.concretepage.validator.UserValidator">
<property name="location" value="messages_en.properties"/>
</bean>
</beans>
Run
SpringDemo.java
package com.concretepage;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;
import org.springframework.validation.MapBindingResult;
import org.springframework.validation.ObjectError;
import com.concretepage.bean.User;
import com.concretepage.validator.UserValidator;
public class SpringDemo {
public static void main(String... args) {
ApplicationContext context = new ClassPathXmlApplicationContext("spring-app.xml");
User user = (User)context.getBean("user");
UserValidator userValidator = (UserValidator)context.getBean("userValidator");
Map<String,String> map = new HashMap<String,String>();
MapBindingResult err = new MapBindingResult(map, User.class.getName());
userValidator.validate(user, err);
List<ObjectError> list = err.getAllErrors();
for(ObjectError objErr : list){
System.out.println(objErr.getDefaultMessage());
}
}
}
Map attributes.
Find the output.
Name can not be blank. The age entered is not valid.
