CallbackHandler (Java Platform SE 7 ) (original) (raw)

An application implements a CallbackHandler and passes it to underlying security services so that they may interact with the application to retrieve specific authentication data, such as usernames and passwords, or to display certain information, such as error and warning messages.

CallbackHandlers are implemented in an application-dependent fashion. For example, implementations for an application with a graphical user interface (GUI) may pop up windows to prompt for requested information or to display error messages. An implementation may also choose to obtain requested information from an alternate source without asking the end user.

Underlying security services make requests for different types of information by passing individual Callbacks to theCallbackHandler. The CallbackHandler implementation decides how to retrieve and display information depending on the Callbacks passed to it. For example, if the underlying service needs a username and password to authenticate a user, it uses a NameCallback andPasswordCallback. The CallbackHandler can then choose to prompt for a username and password serially, or to prompt for both in a single window.

A default CallbackHandler class implementation may be specified in the auth.login.defaultCallbackHandler security property. The security property can be set in the Java security properties file located in the file named <JAVA_HOME>/lib/security/java.security. <JAVA_HOME> refers to the value of the java.home system property, and specifies the directory where the JRE is installed.

If the security property is set to the fully qualified name of aCallbackHandler implementation class, then a LoginContext will load the specifiedCallbackHandler and pass it to the underlying LoginModules. The LoginContext only loads the default handler if it was not provided one.

All default handler implementations must provide a public zero-argument constructor.