ejb3.0 学习笔记

１　A session bean or a message-driven bean can be designed with bean-managed transaction demarcation
or with container-managed transaction demarcation. (But it cannot be both at the same time.)


２　Enterprise JavaBeans defines the following values for the TransactionAttribute metadata annotation:
• MANDATORY
• REQUIRED
• REQUIRES_NEW
• SUPPORTS
• NOT_SUPPORTED
• NEVER


supports : 如果上下文有transactionContext,就需要事务（效果和required一样），如果上下文没有，就不需要事务。（和not_supported一样）

MANDATORY: 是说如果调用上下文没有开启事务，就抛出一个异常，强制需要事务。

never: 如果上下文有开启事务，就抛出异常，表示强制不需要事务，刚好和mandatory相反。


3　写ejb的约束

An enterprise bean must not use read/write static fields. Using read-only static fields is
allowed. Therefore, it is recommended that all static fields in the enterprise bean class be
declared as final.　　不要使用可读写的静态变量，如果要用的，使用final的标记。


An enterprise bean must not use thread synchronization primitives to synchronize execution of
multiple instances.

An enterprise bean must not use the AWT functionality　display, or to input information from a keyboard.

An enterprise bean must not use the java.io package to attempt to access files and directories
in the file system.

An enterprise bean must not attempt to listen on a socket, accept connections on a socket, or
use a socket for multicast.不要使用server端的socket

The enterprise bean must not attempt to query a class to obtain information about the declared
members that are not otherwise accessible to the enterprise bean because of the security rules
of the Java language. The enterprise bean must not attempt to use the Reflection API to access
information that the security rules of the Java programming language make unavailable.不要使用reflection

The enterprise bean must not attempt to create a class loader; obtain the current class loader;
set the context class loader; set security manager; create a new security manager; stop the
JVM; or change the input, output, and error streams.不要去创建classloader或者获取classloader

The enterprise bean must not attempt to manage threads. The enterprise bean must not attempt
to start, stop, suspend, or resume a thread, or to change a thread’s priority or name. The enterprise
bean must not attempt to manage thread groups.不要去管理线程。