Programming WebLogic JDBC
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The following sections describe some common issues when developing JDBC applications:
Check the threading model you are using. Green threads can conflict with the kernel threads used by OCI. When using Oracle drivers, WebLogic recommends that you use native threads. You can specify this by adding the -native
flag when you start Java.
On UNIX, two threading models are available: green threads and native threads. For more information, read about the JDK for the Solaris operating environment on the Sun Web site.
You can determine what type of threads you are using by checking the environment variable called THREADS_TYPE.
If this variable is not set, you can check the shell script in your Java installation bin directory.
Some of the problems are related to the implementation of threads in the JVM for each operating system. Not all JVMs handle operating-system specific threading issues equally well. Here are some hints to avoid thread-related problems:
SHLIB_PATH
. The current JDK can not find the shared library (.sl
) unless the library is in the path defined by SHLIB_PATH
. To check the current value of SHLIB_PATH
, at the command line type: $ echo $SHLIB_PATH
BEA recommends—and good programming practice dictates—that you always close JDBC objects, such as Connections
, Statements
, and ResultSets
, in a finally
block to make sure that your program executes efficiently. Here is a general example:
try {
Driver d =
(Driver)Class.forName("weblogic.jdbc.oci.Driver").newInstance();
Connection conn = d.connect
("jdbc:weblogic:oracle:myserver",
"scott", "tiger");
Statement stmt = conn.createStatement();
stmt.execute("select * from emp");
ResultSet rs = stmt.getResultSet();
// do work
}
catch (Exception e) {
// handle any exceptions as appropriate
}
finally {
try {rs.close();}
catch (Exception rse) {}
try {stmt.close();}
catch (Exception sse) {}
try {conn.close();
catch (Exception cse) {}
}
You should also avoid the following practice, which creates abandoned JDBC objects:
//Do not do this.
stmt.executeQuery();
rs = stmt.getResultSet();
//Do this instead
rs = stmt.executeQuery();
The first line in this example creates a result set that is lost and can be garbage collected immediately.
The following section provides troubleshooting information when using nested triggers on some Microsoft SQL databases:
For information on supported data bases and data base drivers, see Supported Configurations.
You may encounter a SQL Server error indicating that the nesting level has been exceeded on some SQL Server databases.
CREATE TABLE EmployeeEJBTable (name varchar(50) not null,salary int, card varchar(50), primary key (name))
CREATE TABLE CardEJBTable (cardno varchar(50) not null, employee varchar(50), primary key (cardno), foreign key (employee) references EmployeeEJB Table(name) on delete cascade)
CREATE TRIGGER card on EmployeeEJBTable for delete as delete CardEJBTable where employee in (select name from deleted)
CREATE TRIGGER emp on CardEJBTable for delete as delete EmployeeEJBTable where card in (select cardno from deleted)
insert into EmployeeEJBTable values ('1',1000,'1')
insert into CardEJBTable values ('1','1')
DELETE FROM CardEJBTable WHERE cardno = 1
Results in the following error message:
Maximum stored procedure, function, trigger, or view nesting level exceeded (limit 32).
To work around this issue, do the following:
-- Start batch
exec sp_configure 'nested triggers', 0 -- This set's the new value.
reconfigure with override -- This makes the change permanent
-- End batch
exec sp_configure 'nested triggers'
Applications using EJBs with a Microsoft driver may encounter situations when the return code from the execute()
method is 0, when the expected value is 1 (1 record deleted).
CREATE TABLE EmployeeEJBTable (name varchar(50) not null,salary int, card varchar(50), primary key (name))
CREATE TABLE CardEJBTable (cardno varchar(50) not null, employee varchar(50), primary key (cardno), foreign key (employee) references EmployeeEJB Table(name) on delete cascade)
CREATE TRIGGER emp on CardEJBTable for delete as delete EmployeeEJBTable where card in (select cardno from deleted)
insert into EmployeeEJBTable values ('1',1000,'1')
insert into CardEJBTable values ('1','1')
DELETE FROM CardEJBTable WHERE cardno = 1
The EJB code assumes that the record is not found and throws an appropriate error message.
To work around this issue, run the following script:
exec sp_configure 'show advanced options', 1
reconfigure with override
exec sp_configure 'disallow results from triggers',1
reconfigure with override
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