Oracle's JVM in the database, available since 8i and also known as "OJVM" allows you (Developer or DBA) to load Java code into the database and execute it from a database session. Note that any OS calls that it makes will be from the server process, not the client process. Thus, if the code tries to read or write to a filesystem or to connect to an external website, the call will be executed by the database server process, not your client (sqlplus or any other program).
Here is a simple example :
SQL> -- grant Java Code permission to only READ only /home/oracle/tmp
SQL> -- this should have been provided by the DBA
SQL>
SQL> begin
2 dbms_java.grant_permission('HEMANT',
3 'SYS:java.io.FilePermission',
4 '/home/oracle/tmp', 'read');
5
6 dbms_java.grant_permission( 'HEMANT',
7 'SYS:java.io.FilePermission',
8 '/home/oracle/tmp/*',
9 'read' );
10
11 dbms_java.grant_permission( 'HEMANT',
12 'SYS:java.lang.RuntimePermission',
13 'getFileSystemAttributes',
14 '' );
15 end;
16 /
PL/SQL procedure successfully completed.
SQL>
SQL> --
SQL>
SQL> -- here is where I load the Java code into my schema
SQL> connect hemant/hemant@orclpdb1
Connected.
SQL>
SQL> -- load the java code into the database
SQL> create or replace and compile java source named "readOSDirectory"
2 as
3 /* using java.io */
4 import java.io.*;
5
6 /* create the main class */
7 public class readOSDirectory
8 {
9 /* create the class to be executed from a procedure */
10 public static void getList(String directory)
11 {
12 /* use File class from java.io */
13 File directoryPath = new File( directory );
14 File filesList[] = directoryPath.listFiles();
15
16 /* read till end of list */
17 for (File file : filesList)
18 {
19 System.out.println("File Name: "+file.getName()
20 + " File Size: "+file.length());
21 }
22 }
23 }
24 /
Java created.
SQL>
SQL> show errors
No errors.
SQL>
SQL> /* create a PL/SQL procedure to call the getList class */
SQL> create or replace
2 procedure Read_Directory( p_directory in varchar2 )
3 as language java
4 name 'readOSDirectory.getList( java.lang.String )';
5 /
Procedure created.
SQL>
SQL> /* enable output to screen-- serveroutput is for my sqlplus session */
SQL> SET SERVEROUTPUT ON SIZE 100000
SQL> CALL dbms_java.set_output (100000);
Call completed.
SQL>
SQL> begin
2 Read_Directory('/home/oracle/tmp');
3 end;
4 /
File Name: File_1.txt File Size: 13
File Name: File_2.txt File Size: 25
File Name: Run_Sequence_Loop.sql File Size: 1047
File Name: List_LongOps.sql File Size: 303
File Name: create_db_HEMANT.sql File Size: 1530
File Name: create_db_HEMANT.lst File Size: 47
PL/SQL procedure successfully completed.
SQL>
SQL> begin
2 Read_Directory('/home/oracle');
3 end;
4 /
Exception in thread "Root Thread" java.security.AccessControlException: the Permission ("java.io.FilePermission" "/home/oracle"
"read") has not been granted to HEMANT. The PL/SQL to grant this is dbms_java.grant_permission( 'HEMANT',
'SYS:java.io.FilePermission', '/home/oracle', 'read' )
at java.security.AccessControlContext.checkPermission(AccessControlContext.java)
at java.security.AccessController.checkPermission(AccessController.java:926)
at java.lang.SecurityManager.checkPermission(SecurityManager.java:551)
at oracle.aurora.rdbms.SecurityManagerImpl.checkPermission(SecurityManagerImpl.java:210)
at java.lang.SecurityManager.checkRead(SecurityManager.java:890)
at java.io.File.list(File.java:1117)
at java.io.File.listFiles(File.java:1207)
at readOSDirectory.getList(readOSDirectory:11)
begin
*
ERROR at line 1:
ORA-29532: Java call terminated by uncaught Java exception: java.security.AccessControlException: the Permission
("java.io.FilePermission" "/home/oracle" "read") has not been granted to HEMANT. The PL/SQL to grant this is
dbms_java.grant_permission( 'HEMANT', 'SYS:java.io.FilePermission', '/home/oracle', 'read' )
ORA-06512: at "HEMANT.READ_DIRECTORY", line 1
ORA-06512: at line 2
SQL>
SQL> !ls -l /home/oracle/tmp
total 24
-rw-r--r--. 1 oracle oinstall 47 Apr 25 18:46 create_db_HEMANT.lst
-rw-r--r--. 1 oracle oinstall 1530 Apr 25 18:46 create_db_HEMANT.sql
-rw-r--r--. 1 oracle oinstall 13 Apr 25 18:07 File_1.txt
-rw-r--r--. 1 oracle oinstall 25 Apr 25 18:34 File_2.txt
-rw-r--r--. 1 oracle oinstall 303 Apr 25 18:46 List_LongOps.sql
-rw-r--r--. 1 oracle oinstall 1047 Apr 25 18:46 Run_Sequence_Loop.sql
SQL>
(Note : The Java call reads from the OS's directory object "as is" returned by the directory. The "ls -l" command sorts the output, so you may see a difference in the sorted output)
Since OJVM runs in a database server process, strong permission controls are enforced. So, the first set of calls show permissions being granted by the DBA to the "HEMANT" schema to only read from /home/oracle/tmp
Then, the user (HEMANT) connects and loads his Java code into the database. (Note : The first time you run this, it may take some time to load the java classes). Then he creates a PL/SQL procedure as a "wrapper" that can execute the Java code.
Finally, he executes the java code to read the target directory /home/oracle/tmp
I also demonstrate how his attempt to read /home/oracle fails as he has not been granted explicit permission on this directory