what is java:comp/env?

Question

what is meant by java:comp/env ?

What does the look up like :

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

do ?

I understand that a look-up like :

(DataSource)envContext.lookup("jdbc/MyDatasource")

looks up for the name MyDatasource in the context.xml or web.xml to get the URL of the database. Is it so ? !! But what does the former look up do ?

**Please open and read the link before voting to close this question. Dont just go after the title.** — saplingPro, Jul 24 '12 at 13:51
It sure looks like an answer to me. It's a root namespace provided by the container for you to look up your resources in. — user207421, Jul 25 '12 at 03:37
This is a good question for people trying to migrate from Weblogic to Tomcat for example — ACV, Jul 24 '17 at 11:41

score 74 · Accepted Answer · edited May 15 '13 at 22:08

74

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.

edited May 15 '13 at 22:08

Arjan Tijms

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answered Jul 24 '12 at 13:41

JB Nizet

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What is _this_ node meant for ? There would be many nodes in the JNDI tree. – saplingPro Jul 24 '12 at 13:53
11

I still don't get the feel of what actually is `java:comp/env`. – saplingPro Jul 24 '12 at 13:54
10

Each JEE component (webapp, EJB) can define properties that are local to this component. And these properties are accessible through `java:comp/env`. See http://tomcat.apache.org/tomcat-7.0-doc/jndi-resources-howto.html#web.xml_configuration for example. EJBs have the same sort of thing. – JB Nizet Jul 24 '12 at 15:02

score 9 · Answer 2 · edited Jul 24 '17 at 11:49

9

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

edited Jul 24 '17 at 11:49

ACV

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answered Nov 18 '15 at 03:38

Rich

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score 6 · Answer 3 · answered Feb 23 '21 at 00:55

6

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.

answered Feb 23 '21 at 00:55

joker

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this should be the accepted answer - clear explanation. – likejudo Jun 02 '21 at 16:45
@joker: The link you shared from Sun Java System Application Server is a very useful source to understand the jargon in JNDI. I can hardly find it in tomcat docs while setting it as it never explained much there. I found the Admin Guide as well in the Sun link, it clears the whole picture. Thanks. – sylye Sep 28 '21 at 08:05

what is java:comp/env?

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