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Validating user input
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<h:form> <h:panelGroup rendered="#{loggedIn}"> Current user: <b>#{currentUser.username}</b> (<h:commandLink value="Logout" action="#{login.doLogout}"/>) </h:panelGroup> </h:form>
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The expression #{loggedIn} resolves to the boolean context variable loggedIn that is either present in the session context or not. The login/logout functionality of the application is now complete. Pages and component methods are secured; only a logged-in user can open and call them. How do people get user accounts They have to fill out a registration form. You must validate the form data and create the account in the database.
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17.4 Validating user input
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In the previous example, the login screen and login/logout code, you rely on standard JSF validators and your own code in the doLogin() method to validate user input. When a user submits the login form, JSF runs the declared validators (in login.xhtml) in the Process Validations phase. If the user enters a username and a password, validation is successful, and the login.doLogin() method executes. The given username and password are bound to the database query. User input is validated twice:
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JSF validates the HTML form input before it synchronizes the value of each input field with the bound model, the currentUser in the Seam session context. If you access currentUser later in an action method, you have the guarantee that the validation rules of your pages have been checked.
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The JDBC driver validates the user input when you bind the username and password to the JPA QL query. Internally, this is a binding to a regular JDBC PreparedStatement, so the JDBC driver escapes any dangerous characters that the user may have entered.
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Validating user input in the presentation layer and ensuring that no SQL injection attacks are possible is good enough for a simple login screen. But what if you need to validate a User object before it s saved in the database for example, during an account registration procedure You need more complex validation: You have to check the length of the entered username and see whether any illegal characters have been used, and you also need to validate the quality of the password. All this can be solved with more
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and possibly custom validation in the JSF presentation layer, but the database schema also must validate the integrity of stored data. For example, you create database constraints that limit the length of the value stored in the USERNAME column or require a successful string-pattern match. In any sophisticated application, input validation is a concern that needs to be handled not only in the presentation layer, but in several layers and even in different tiers. It s a crosscutting concern that can affect all your code. With Hibernate Validator, you can isolate and encapsulate validation and data integrity rules easily, for all application layers.
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17.4.1 Introducing Hibernate Validator
Hibernate Validator is a module of Hibernate Annotations. You can use Hibernate Validator even without Hibernate and Seam, with only hibernate3.jar and hibernate-annotations.jar on your classpath, in any Java application. (It s likely that Hibernate Validator will be forked into its own stand-alone module in the future. This depends on the work done in JSR 303, Bean Validation ; see http://jcp.org/en/jsr/detail id=303.) Hibernate Validator is a set of annotations you apply to your domain model to define data validation and integrity rules declaratively. You can extend Hibernate Validator with your own constraints, by writing your own annotations. These applied integrity and validation rules can be used with the following:
Plain Java You can call the ClassValidator API anywhere in Java code and supply objects that need to be checked. The validator either completes validation or returns an array of InvalidValue objects. Each InvalidValue contains the details about the validation failure, such as the property name and error message. Hibernate In native Hibernate, you can register Hibernate Validator events that hook into the internal processing of Hibernate persistence operations. With these events, Hibernate can validate any object you re inserting or updating in the database automatically and transparently. An InvalidStateException that contains the details is thrown when validation fails. Hibernate EntityManager If you use the Java Persistence API with Hibernate EntityManager, the Hibernate Validator events are activated by default, and all entity instances are checked against the validation annotations when you insert or update an object in the database. SchemaExport Hibernate s database schema-generation feature can create database constraints that reflect your integrity rules in SQL DDL. The
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