Best ways of performing server side validations on data using Java

Could someone guide me on this fundamental question: What are the best way ways of performing server side validations on data using Java?

I would like 开发者_JS百科to know if there are open source libraries available to perform server side validations as well.

Any help is appreciated.

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It depends on which web developement framework you are using.

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Raw JSP Servlet

If you are using simple jsp servlet, Then I would suggest add one validator package/jar for each form/jsp screen. and validate it from controller before passing to service.

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JSF

If you are using JSF then there is very well designed validation phase provided , You can use ready made validators (you can just add annotation on the form field and its done) or you can create your own validators also.

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Spring MVC

If you are using Spring MVC , it has also got a saperate layer for validation.

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Struts

Struts has also got saperate layer for validation

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If you are looking to validate POJOs, you can have a look at the Oval framework http://oval.sourceforge.net/

JSR-303 (and its implementations) may also help if ur app is designed based on pojos or beans

Here is a sample custom validation in OVal: Lets say you have to validate variables map in SomeValueClass and ensure the value of key 'greeting' is always present.

public class SomeValueClass {

@FormCollection
Map variables;


public static void main(String[] args) {
    SomeValueClass svc1 = new SomeValueClass();
    svc1.variables = new HashMap();
    svc1.variables.put("greeting", "");

    Validator validator = new Validator();
    List<ConstraintViolation> violations = validator.validate(svc1);
    System.out.println("svc1 violations.size() = " + violations.size());
}

The @FormCollection annotation on "Map variables;" is a custom validator and is as below:

@Retention(RetentionPolicy.RUNTIME)
@Target({ElementType.FIELD, ElementType.PARAMETER, ElementType.METHOD})
@net.sf.oval.configuration.annotation.Constraint(checkWith = FormCollectionCheck.class)
public @interface FormCollection {
  String message() default "Some errors in the form";
}

And the constraint check class will look like this:

public class FormCollectionCheck extends AbstractAnnotationCheck<FormCollection> {
  public boolean isSatisfied(Object validatedObject, Object valueToValidate, OValContext context, Validator validator) {
    Map vars = (Map) valueToValidate;
    return !(vars.get("greeting")==null || ((String)vars.get("greeting")).length()<=0);
  }
}

Hope that helps, Cheers

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then you go for the framework which are providing inbuilt validations like struts etc. Those will provide you validation component. Also its an opensource.