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6.3.4 The pros and cons of BMT
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CMT is the default transaction type for EJB transactions. In general, BMT should
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be used sparingly because it is verbose, complex, and difficult to maintain. There are some concrete reasons to use BMT, however. BMT transactions need not begin and end in the confines of a single method call. If you are using a stateful session bean and need to maintain a transaction across method calls, BMT is your only option. Be warned, however, that this technique is complicated and error prone and you might be better off rewriting your application rather than attempting this. Can you spot a bug in listing 6.3 The last catch block did not roll back the transaction as all the other catch blocks did. But even that is not enough; what if the code throws an error (rather than an exception) Whichever way you do it, it is error prone and we recommend using CMT instead. Another argument for BMT is that you can fine-tune your transaction boundaries so that the data held by your code is isolated for the shortest time possible. Our opinion is that this idea indulges in premature optimization, and again, you are probably better off refactoring your methods to be smaller and more specific anyway. Another drawback for BMT is the fact that it can never join an existing transaction. Existing transactions are always suspended when calling a BMT method, significantly limiting flexible component reuse. This wraps up our discussion of EJB transaction management. It is now time to turn our attention to another critical aspect of enterprise Java development: security.
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Transactions and security
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6.4 Exploring EJB security
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Securing enterprise data has always been a primary application development concern. This is especially true today in the age of sophisticated cyber-world hackers, phishers, and identity/data thieves. Consequently, security is a major concern in developing robust Java EE solutions. EJB has a security model that is elegant, flexible, and portable across heterogeneous systems. In the remainder of this chapter, we ll explore some basic security concepts such as authentication and authorization, users, and groups, and we ll investigate the Java EE/EJB security framework. We ll also take a look at both declarative and programmatic security in EJB 3. Let s start with two of the most basic ideas in security: authentication and authorization.
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6.4.1 Authentication vs. authorization Securing an application involves two primary functions: authentication and authorization. Authentication must be done before authorization can be performed, but as you ll see, both are necessary aspects of application security. Let s explore both of these concepts.
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Authentication Authentication is the process of verifying user identity. By authenticating yourself, you prove that you are who you say you are. In the real world, this is usually accomplished through visual inspection/identity cards, signature/handwriting, fingerprint checks, and even DNA tests. In the computer world, the most common method of authentication is by checking username and password. All security is meaningless if someone can log onto a system with a false identity. Authorization Authorization is the process of determining whether a user has access to a particular resource or task, and it comes into play once a user is authenticated. In an open system, an authenticated user can access any resource. In a realistic security environment, this all-or-nothing approach would be highly ineffective. Therefore, most systems must restrict access to resources based on user identity. Although there might be some resources in a system that are accessible to all, most resources should be accessed only by a limited group of people. Both authentication and authorization, but especially authorization, are closely tied to other security concepts, namely users, groups, and roles, which we ll look at next.
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Exploring EJB security
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6.4.2 Users, groups, and roles
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To perform efficient and maintainable authorization, it is best if you can organize users into some kind of grouping. Otherwise, each resource must have an associated list of all the users that can access it. In a nontrivial system, this would easily become an administrator s nightmare. To avoid this problem, users are organized into groups and groups as a whole are assigned access to resources, making the access list for an individual resource much more manageable. The concept of role is closely related to the concept of group, but is a bit tricky to understand. For an EJB application, roles are much more critical than users and groups. To understand the distinction, consider the fact that you might not be building an in-house solution but a packaged Java EE application. Consequently, you might not know the exact operational environment your application will be deployed in once it is purchased by the customer. As a result, it s impossible for you to code for the specific group names a customer s system administrator will choose. Neither should you care about groups. What you do care about is what role a particular user in a group plays for your application. In the customer system, user Joe might belong to the system group called peons. Now assume that an ActionBazaar integrated B2B Enterprise Purchasing System is installed on the customer s site. Among other things, this type of B2B installation transparently logs in all existing users from the customer system into the ActionBazaar site through a custom desktop shortcut. Once logged in, from ActionBazaar s perspective, Joe could simply be a buyer who buys items online on behalf of the B2B customer company. To another small application in the operational environment, user Joe might be an administrator who changes system-wide settings. For each deployed application in the operational environment, it is the responsibility of the system administrator to determine what system group should be mapped to what application role. In the Java EE world, this is typically done through vendorspecific administrative interfaces. As a developer, you simply need to define what roles your application s users have and leave the rest to the assembler or deployer. For ActionBazaar, roles can be buyers, sellers, administrators, and so on. Let s solidify our understanding of application security in EJB using an ActionBazaar example.
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