what is java:comp/env?

java jakarta-ee jndi
saplingPro picture saplingPro · Jul 24, 2012 · Viewed 83.4k times · Source

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 ?

Answer

JB Nizet picture JB Nizet · Jul 24, 2012

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.

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