什么是 java: comp/env？

小开

最佳答案

java:comp/env is the node in the JNDI tree where you can find properties for the current Java EE component (a webapp, or an EJB).

Context envContext = (Context)initContext.lookup("java:comp/env");

allows defining a variable pointing directly to this node. It allows doing

SomeBean s = (SomeBean) envContext.lookup("ejb/someBean");
DataSource ds = (DataSource) envContext.lookup("jdbc/dataSource");

rather than

SomeBean s = (SomeBean) initContext.lookup("java:comp/env/ejb/someBean");
DataSource ds = (DataSource) initContext.lookup("java:comp/env/jdbc/dataSource");

Relative paths instead of absolute paths. That's what it's used for.

小开

It's an in-memory global hashtable where you can store global variables by name.

The "java:" url scheme causes JNDI to look for a javaURLContextFactory class, which is usually provided by your app container, e.g. here is Tomcat's implementation javadoc

See also NamingManager.getURLContext

小开

I know I'm far late, but I was asking the same question, and I think I came some answer. So, if I may put my two cents.

java:comp/env/jdbc/myDataSource

java: is just like jdbc: from connection string. Acts as a protocol.
comp is the root for all JNDI contexts.
env is the subcontext for all resource related. There is another for user. Check this out.
jdbc is the subcontext for jdbc resources. There are types. Check the link from the previous bullet.
myDataSource is the name of your jdbc resource.