Author Archives: Jesper Udby

About Jesper Udby

I'm a freelance computer Geek living in Denmark with my wife and 3 kids. I've done professional software development since 1994 and JAVA development since 1998.

Simple logarithm implementation in PIC assembler

Most natural observations are exponentational/logarithmic in nature. I often do simple hardware using Microchip PIC processors (usually 12F or 16F families). Hardware doing some business in the home. One such example is my Christmas-tree-lightning-controller. Basically it only turns my electric … Continue reading

Posted in Microcontoller, Open Source, Personal, PIC | Tagged , , | 4 Comments

Locking a row, portable between databases, with JDBC

A couple of years ago I was with a project designing a system to manage Investor Meetings. An Investor must have a valid Pass in order to join a Meeting. Each Pass has a unique serial number. It was a … Continue reading

Posted in Databases, Java | Tagged , , , , , | 1 Comment

Squareroot (sqrt) with BigDecimal

Recently I was refactoring some code from using double to using BigDecimal and suddenly needed a square root method. I remembered years ago I was taught a simple “successive approximation” method; believe it was grammar school. I searched the net … Continue reading

Posted in Java | Tagged , | 2 Comments

Implementing a simple database semaphore

In this article I will describe a simple technique that enables you to implement an “exclusive lock” in a distributed, even clustered, environment. The technique works with all major databases, and should work with any database that has a reasonable … Continue reading

Posted in Databases, Java | Tagged , , , , , , , , | 11 Comments

Financial (monetary) computations using floating point arithmetic [in JAVA]

In this article, I will discuss some of the issues in doing financial calculations in JAVA. The issues are not related to JAVA only, but to any calculation done in a “computer language” using binary floating point arithmetic, including calculations … Continue reading

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Securing J[2]EE applications, part 3

In this third article, the samples are modified to be run on JBoss (4.0.3+) and JavaDB (Derby version 10.2). The first article showed how to setup Glassfish authentication with only a single database table. The second article evovled the simple … Continue reading

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Securing J[2]EE applications, part 2

The first part, Securing J[2]EE applications, part 1, discusses a simple setup where a single database table, 2 views and a correctly configured jdbcRealm could handle the most basic authentication and authorization requirements. This second article discusses a few enhancements … Continue reading

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Securing J[2]EE applications, part 1

I’m writing a few articles about securing J2EE applications. The setup is a Glassfish v2 as application server and PostgreSQL v8.3 as database server, keeping it open-source and free 🙂 This first part discusses a simple setup where only a … Continue reading

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Trusting any “secure” host

My main concern is developing server-side JAVA-applications: J[2]EE applications. When working with hobby-projects, I’m often faced with situations where I need to call other “third-party” applications over HTTP, in order to obtain some information important to me in specific situations. … Continue reading

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Writing JDBC code: resource cleanup and exception handling

No matter how nice an ORM tool used in the project, CMP, Hibernate or JPA, You will eventually have to start writing “low-level” JDBC code. Most often for performance reasons, sometimes just to utilize some database-vendor-specific feature. Or calling stored … Continue reading

Posted in Databases, Java | Tagged , | 1 Comment