How to Java

See Oracle Managed Errors for Java related errors on Oracle

Verify installation
select count(*) from dba_registry where comp_id = 'JAVAVM'

Install JServer 
java_pool_size >30M and shared_pool_size >50M INIT.ORA parameter values.

[s.sql]
alter system flush shared_pool;
@?/javavm/install/initjvm.sql
#this is optional, and at the moment not tested
@?/javavm/install/catjava.sql
alter system flush shared_pool;
exit

nohup sqlplus "/ as sysdba" @s &

Grants
GRANT JAVAUSERPRIV TO SCOTT;

Removing JVM
nohup sqlplus "/ as sysdba" @?/javavm/install/rmjvm.sql &
alter system flush shared_pool;
A shutdown abort is often required 

Supplied removal sucks! Let's do it by hand.
This manual way works!
Remove anything from obj$ relating java (^^lol!)
#do not remove SYS.JAVASNM$ this table is needed by package rmjvm
drop table sys.JAVA$RMJVM$AUX3;
drop table sys.JAVA$RMJVM$AUX2;
drop table sys.JAVA$RMJVM$AUX;
drop table sys.JAVA$JVM$STEPS$DONE;
drop table sys.JAVA$JVM$STATUS;
drop package sys.RMJVM;
drop package sys.INITJVMAUX;

Installing with loadjava
#After loading reconnect any client java user, the old classes may be used. Flushing the shared pool does not works
#using SID
loadjava -thin -user "periscope/periscope@172.18.20.68:1521:CLAR" -grant public -r -v -f servlet.jar
#using SERVICE NAME
loadjava -thin -user "strmadmin/strmadmin@dbd0227-grid.nl.eu.abnamro.com:1521/mtg.a.de.grid" -grant public -r -v -f CaptureMTS.jar

-genmissing
Use this option when a class is not present, but required, and you want it to be automatically generated

Removing single classes
select 'DROP JAVA CLASS "' || owner || '"."' || name || '";' 
from dba_java_classes
where name like 'javax/servlet/%'
and owner='PERISCOPE'

DROP JAVA CLASS "PERISCOPE"."javax/servlet/ServletInputStream";

Troubleshooting
DOC>*/
call rmjvm.check_for_rmjvm()
     *
ERROR at line 1:
ORA-00028: your session has been killed
ORA-06512: at "SYS.RMJVM", line 447

-------

restart db, remove, restart db, install

Redirecting Output on the Server
--From sqlplus:
SET SERVEROUTPUT ON SIZE 5000
CALL dbms_java.set_output(5000);

Test class
CREATE OR REPLACE AND RESOLVE JAVA SOURCE NAMED Test as
public class Test {
  public static void main (String args[]) {
    System.out.println("This is a test");
  }
}

Compile classes
SQL> ALTER java class PERISCOPE."com/periscope/core/ConnectionBean" COMPILE;
Warning: Java altered with compilation errors.
SQL> show errors java class PERISCOPE."com/periscope/core/ConnectionBean";  

Compile sources
SQL> ALTER java source PERISCOPE."Generated/TESTSTAPI" compile;
Warning: Java altered with compilation errors.
SQL> show error java source PERISCOPE."Generated/TESTSTAPI"

Static variables
Java static variables are retained for the entire Oracle session duration, and are not shared with other sessions. 
This allow the creation of a session repository. Allocation occurs in PGA. 
Be very aware of possible session state clear...

Are we on the server?
System.getProperty ("oracle.jserver.version")

JDBC Connection tips
!!Do not span connect string on multiple lines!!
    
Connect String - standard
#for sysdba you must use Properties.put("internal_logon", "sysdba");
jdbc:oracle:thin:@ + hostname + : + port + : + sid

Connect String - load balanced
jdbc:oracle:thin:@(DESCRIPTION=(LOAD_BALANCE=on)(ADDRESS=(PROTOCOL=TCP)(HOST=host1)(PORT=1521))(ADDRESS=(PROTOCOL=TCP)(HOST=host2)(PORT=1522))(CONNECT_DATA=(SERVICE_NAME=al12)))

Permissions
begin
dbms_java.grant_permission('SYSTEM','java.io.FilePermission','/usr/bin/*','read ,write, execute, delete');
end; 

select * from DBA_JAVA_POLICY
where grantee = 'SYSTEM'

begin
dbms_java.revoke_permission('SYSTEM','java.io.FilePermission','/usr/bin/*','read ,write, execute, delete');
end; 

select enabled, seq from DBA_JAVA_POLICY
where grantee = 'SYSTEM'

begin
DBMS_JAVA.DISABLE_PERMISSION(59);
dbms_java.delete_permission(59); 
end;
#or
delete from java$policy$ where key in (181, 182, 183, 201);
commit;
alter system flush shared_pool;