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Tracking Application Module Pool operations

Posted on Thursday, November 20 2014 at 06:53 | Category: Oracle ADF & JDeveloper | 0 Comment(s)

To get a better understanding how the Application Module Pool works in Oracle ADF, it can be useful to log some of its methods as they are called. This can also be useful to track down Application Module Pool related issues, or even to collect usage and performance statistics.

The entry point for such a logging facility is to define a custom Application Module Pool class. Note that this is not something you would or should do in the final application - it is usually not necessary, but can be convenient for the use cases mentioned above. The class to instantiate as the Application Module Pool is defined through the PoolClassName property on the Application Module's configuration:

The configuration is stored in the bc4j.xml configuration file, and we could also set the property by simply editing this file:


  <appmoduleconfig deployplatform="LOCAL" jdbcname="ApplicationDB" jbo.project="model.Model" name="AppModuleLocal" applicationname="model.AppModule">
     <am-pooling poolclassname="test.CustomApplicationModulePool">
     <database jbo.locking.mode="optimistic">
     <security appmodulejndiname="model.AppModule">
  </security></database></am-pooling></appmoduleconfig>

Now, the ADF runtime will instantiate an object of the defined class as the Application Module's pool. We simply need to implement this class, inheriting from ApplicationPoolImpl:


package test;

import java.util.Properties;
import oracle.jbo.ApplicationModule;
import oracle.jbo.common.ampool.ApplicationPoolImpl;
import oracle.jbo.common.ampool.SessionCookie;

public class CustomApplicationModulePool extends ApplicationPoolImpl {
    public CustomApplicationModulePool() {
        super();
    }

    ...

}

By overriding the methods which are of interest, we can add logging to the application module pool and for example track how Application Modules are checked out and released. Ideally a logging API such as java.util.logging should be used - for simplicity, I am using System.err in the examples. The most interesting methods to track Application Module usage are useApplicationModule() which is called by the framework to check out an application module from the pool, releaseApplicationModule() which is called to give back an application module to the pool and probably createSessionCookie() which creates a session cookie for a BC4J session:


    @Override
    public SessionCookie createSessionCookie(String applicationId,
                                             String sessionId,
                                             Properties properties) {
        System.err.printf("createSessionCookie(applicationId=%s, sessionId=%s, properties=%s)\n",
                           applicationId, sessionId, properties);

        SessionCookie result = super.createSessionCookie(applicationId, sessionId, properties);

        System.err.printf("    Result: %s\n", result.getSessionId());

        return result;
    }


    @Override
    public ApplicationModule useApplicationModule(final SessionCookie cookie,
                                                  final boolean checkout) {
        System.err.printf("useApplicationModule(session id=%s, checkout=%s)\n", 
                          cookie.getSessionId(), checkout);

        ApplicationModule result = super.useApplicationModule(cookie, checkout);

        System.err.printf("    Result: %s\n", System.identityHashCode(result));

        return result;
    }

    @Override
    public void releaseApplicationModule(SessionCookie cookie,
                                         boolean manageState) {
        System.err.printf("releaseApplicationModule(cookie=%s, manageState=%s)\n",
                          cookie, manageState);

        super.releaseApplicationModule(cookie, manageState);
    }

    @Override
    public void releaseApplicationModule(SessionCookie cookie,
                                         int releaseFlags) {
        System.err.printf("releaseApplicationModule(cookie=%s, releaseFlags=%s)\n",
                          cookie, releaseFlags);

        super.releaseApplicationModule(cookie, releaseFlags);
    }

We can now observe how and when the ADF runtime retrieves Application Modules form the pool. Remember that each HTTP request which requires BC4J will result in an Application Module checkout and a corresponding release before the request finishes. Also remember that each Application Module has its own database transaction (unless it is a nested Application Module, in which case it inherits the transaction from its parent). Hence, logging information about the associated database transaction can also be useful.


Using Lambdas to implement a function table

Posted on Monday, November 17 2014 at 08:28 | Category: Java | 0 Comment(s)

When I implemented an expression parser for arithmetic expressions (such as t*x+sin(x-5) + π), one part was to create a symbol table to look up constant values such as π, variables such as x and t, but also functions like sin(x). My initial approach had this structure:

 

This allowed me to create a symbol table as a HashMap, and then to add variables, constants or functions into the table:


private Map<String, Symbol> table = new HashMap<>();
...
table.put("sin",  new SinFunction());
table.put("log",  new LogFunction());
...

This works well, but requires a whole new class for each new function, where each of the classes simply provides a getValue() method which delegates to the corresponding static method from Math:

public double getValue(double arg) {
   return Math.sin(arg);
}

Using lambda expressions, the class structure can be much simplified:

Instead of an abstract class Function with specific sub classes which implement the getValue() method, we provide a concrete Function class which delegates to the functional interface DoubleFunction. The instantiation of the Function objects can then be moved into the SymbolTable class, essentially as a convenient method:


public void putSymbol(String name, DoubleFunction<Double> fun) {
   table.put(name, new Function(name, fun));
}

Now, adding new function to the symbol table is straight forward, using a lambda expression:

symbolTable.putSymbol("sin", x -> Math.sin(x));
symbolTable.putSymbol("log", x -> Math.log(x));

Especially we do not need to add another class when adding a new function. The class structure of the symbol table remains stable, all we need is to register the new function through a call to SymbolTable.putSymbol().

Besides simply mapping a function name to a method from the Math class, this works equally well for any user defined function, for example:

symbolTable.putSymbol("f1", x -> x*x + 42*x + 19);
symbolTable.putSymbol("f2", x -> Math.cos(x*x) + 42*x);

Since the Function class holds a reference to the lambda expression through the DoubleFunction interface, we simply call the DoubleFunction.apply() method to evaluate the function for a given x value:

public class Function extends Symbol {

   private DoubleFunction<Double> theFunc;

   ...

   @Override
   public double getValue(double x) {
      return theFunc.apply(x);
   }
}

Enabling global breakpoints in JDeveloper

Posted on Friday, November 07 2014 at 10:21 | Category: Oracle ADF & JDeveloper | 0 Comment(s)

In larger ADF projects with more than one workspace and with many projects, it might happen that a breakpoint can not be set on a class from a different workspace or project, even though JDeveloper properly navigates to the source file.

In this case, make sure that the "Scope for New Breakpoints" is set to "Global" in the "Debugger/Breakpoints" preferences (open the preferences dialog through "Tools/Preferences"):

 


In Hierarchical queries using the Oracle RDBMS - Determine ordering within each level, I showed how to sort the rows of a hierarchical SQL query within each tree level by using ORDER SIBLINGS BY instead of ORDER BY.

There is one detail to keep in mind, though: even the ORDER SIBLINGS BY is done on the overall result of the query, which can cause problems when using UNION ALL to take additional rows into the result:

SELECT 0, 0, 'xyz' FROM DUAL
UNION ALL
SELECT LEVEL, Id, substr( LPAD (' ', 3 * (LEVEL - 1)) || Label, 0, 30) Node
FROM TreeNode
START WITH Parent = 0
CONNECT BY PRIOR Id = Parent
ORDER SIBLINGS BY Label;
ERROR at line 7:
ORA-30929: ORDER SIBLINGS BY clause not allowed here

Using parantheses to explicitly group the second select within the UNION ALL does not help, but there is a simple solution: just wrap the hierarchical query into a sub select, and then do a SELECT * from the sub select:

SELECT 0, 0, 'xyz' FROM DUAL
UNION ALL
SELECT * FROM (
	SELECT LEVEL, Id, substr( LPAD (' ', 3 * (LEVEL - 1)) || Label, 0, 30) Node
	FROM TreeNode
	START WITH Parent = 0
	CONNECT BY PRIOR Id = Parent
	ORDER SIBLINGS BY Label
);
                 0                  0 'XYZ'
------------------ ------------------ ---------
                 0                  0 xyz
                 1                  1 Root Node
                 2                  2    Node 1
                 3                  3       Node 1.1
                 3                  4       Node 1.2
...

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