Develop Reference

JUnit without inversion of control

Currently the JUnit5 Framework works with Inversion of Control. I.e. you annotate a test method with #Test and then JUnit scans your classpath (in the simplest case)
Now is there a way for me to be in charge of calling the test cases through JUnit APIs? Maybe by hooking my test implementations to some test registry provided by JUnit?
I'm pretty new to JUnit - how did older versions go about this?
The reason I'm asking is that normally to execute my test cases, I'd have to run something along the lines of
java -jar junit-platform-standalone.jar --class-path target --scan-class-path
on the command line. My situation requires me to run the test cases through by executing one of my own classes, like that e.g.
java /com/example/MyTestCassesLauncher
EDIT: to clarify, I need one of my own classes to be hosting/launching my test cases, something like this:
// Maybe this needs to extend one of JUnit's launchers?
public class MyTestCassesLauncher {
public static void main(String[] args) {
JUnitLauncher.launchTests(new MyTestClass());
}
}
where JUnitLauncher.launchTests is some kind of API provided by the platform. I'm not looking for a method with that exact same signature but a mechanism that would allow me to ultimately call my own MyTestClassesLauncher class to run the tests.
Thanks in advance.

Not sure what you arę actually trying to achieve but in Junit5 to change behaviour of your tests you can use Extensions mechanism, similar to Junit4 RunWith but more powerful
Such custom extension can provide some additional logic like in this logging example
public class LoggingExtension implements
TestInstancePostProcessor {
#Override
public void postProcessTestInstance(Object testInstance,
ExtensionContext context) throws Exception {
Logger logger = LogManager.getLogger(testInstance.getClass());
testInstance.getClass()
.getMethod("setLogger", Logger.class)
.invoke(testInstance, logger);
}
}
The way Junit controls it's flow is Junit problem - you should not modify framework but extend it

log4j2 extending Logger class

I am trying to migrate from Log4j 1.7 to Log4j2.4
In 1.7, I as creating AppLogger class by extending org.apache.log4j.Logger and using extending debug/error/fatal Methods
e.g.,
public void error(Object message) {
Object error = message;
if (message instanceof Exception) {
Exception e = (Exception) message;
StringWriter sw = new StringWriter();
e.printStackTrace(new PrintWriter(sw));
error = sw.toString();
}
super.error(error);
}
But in Log4j 2.x, I am not able to extend the class org.apache.logging.log4j.Logger;
What is the Best way to achieve this?

I can understand why you might have wanted to do this with Log4j 1.x, but I cannot figure out why you would want to do this with log4j 2. The best place to do this is in a Layout, but most already do this.

As Ralph pointed out, Log4j2 has a very rich set of functionality, and if you go over the documentation, you often find that you can achieve your goals using the built-in layouts, lookups, filters and other features.
Writing a custom lookup only takes a few lines of code and gives you a powerful hook into the logging subsystem which you can use for many purposes.
If you really want to extend Logger for whatever reason, be aware that some layouts require Log4j to walk the stacktrace to report which class and line in your code from the logger was called from. This mechanism is a bit complex and in general I would recommend you create a Logger wrapper instead of extending it. (Prefer delegation to subclassing.)
Log4j has a tool to make this easy for you: the Custom Logger Generator tool documented in the Custom Log Levels page. Try this and see if it gives you what you need.

How to override java.util.logging.Logger to my private logger?

I have code fetched from jar that uses java.util.logging.Logger.
Jar contains about 1000 logger usages and each class start from:
private static final Logger LOG = Logger.getLogger(SomeClass.class.getName());
I want to handle all logs there, means, to point them to my Logger usage and not to java.util.logging.Logger.
Therefore I wrote my own logger.
So instead:
LOG.log(Level.SEVERE, "Error sleeping", e);
I can write:
MyLogger.toLog(TLogLevel.WFS_ERROR, "Monkey", "Error sleeping", e );
The problem is I need run over all java files and replace with mine.
Messy way, hmm
Does anyone know how can by easy way to convert java.util.logging.Logger to com.boo.MyLogger?
Thanks,

The SLF4J project has a jul-to-slf4j bridge that can be used to redirect java.util.logging.Logger calls to SLF4J. You could use that (by making your MyLogger implement the interface defined by SLF4J).
Note that, however, unlike all other logging libraries, j.u.l. is hard-wired into the Java class libraries and cannot be bridged without a performance penalty.
Also, I don't know what you are doing with MyLogger, but usually there is no need to write your own. There are plenty of logging implementations to choose from, and they can be configured in many different ways. And even if you do have to write your own Logger implementation, you should use an existing interface (such as SLF4J which seems to most popular these days).

Take a look at SLF4J:
The Simple Logging Facade for Java or (SLF4J) serves as a simple
facade or abstraction for various logging frameworks, e.g.
java.util.logging, log4j and logback, allowing the end user to plug in
the desired logging framework at deployment time.
Using that you could then also use logback (same author) to log to a common logging framework using the various bridges already available. Or, write your own, but either way you would not have to worry about replacing all that code...

Oracle's Java 7 Logger is configurable, its implementation is simply:
public static Logger getLogger(String name) {
// This method is intentionally not a wrapper around a call
// to getLogger(name, resourceBundleName). If it were then
// this sequence:
//
// getLogger("Foo", "resourceBundleForFoo");
// getLogger("Foo");
//
// would throw an IllegalArgumentException in the second call
// because the wrapper would result in an attempt to replace
// the existing "resourceBundleForFoo" with null.
LogManager manager = LogManager.getLogManager();
return manager.demandLogger(name);
}
So you can also via code set a logging level; besides declarative.
LogManager.getLogManager().getLogger(Logger.GLOBAL_LOGGER_NAME).setLevel(Level.INFO);
Lars Vogel has a nice page, also with its own Logger class.
All put together is quite workable, but maybe sometimes somewhat hard to understand.

Writing a simple print method for debugging in Java

Before I reinvent the wheel - I want to be able to insert debugging traces in my code, such as say("We are here.");, without defining static void say() in every class. It needs to do System.out.println(s), and to be globally switched on or off (doSay(false)), and I'd also like it to be able to identify the class from which it's being invoked (as described here). For example:
MyClass: We are here.
Does Java already have such a tool?

Use SLF4j, not log4j (at least, not directly). They are both created by the same author, Ceki Gülcü, but SLF4J incorporates knowledge gained by seeing log4j in use, and looking at advances in other logging packages.
SLF4J is a common API for a number of different underlying logging systems, like log4j, the java.util.logging package, etc. It also has its own "native" implementation, logback.
One reason I like it better than log4j is its support for message templates. These keep your code simpler.
Also, it allows me to include logging in a library, but let the user of my library choose the logging implementation. Without something like this, a user might have to configure logging just for my library, and it wouldn't be unified with the rest of his application.

The most popular Java logging framework is Log4J which does this (and much more).
Look here for a list of other.

Yes. It's called a logging framework. Java has java.util.logging. But many prefer using Log4J.

You could use a logger like Apache's Log4J and do something like logger.trace("We are here");. When you want that off, set the log level higher (debug, warn, error) in your configuration and the trace logs will disappear.

Java has more advanced logging tools, like log4j or logback. There you should create a public static final Logger logger = Logger.getLogger(..) and use the logger to write debug/info/warn/error messages to wherever you like. They are highly configurable - what and where to log.
For the simpler case (if this is a toy project), you can simply define a class with the public static void log(..) method and use it from every class.

Why not static-declare a function in your Main.java, and use it allround?
public class Main {
private static boolean debug;
public static void setDebug(boolean d) { Main.debug = d; }
public static void say(String s) { if(Main.debug) System.out.println(s); }
}
Let me know if this fits your needs.
Edit: revised the code

I didn't know about static import! I combined ideas from #ninetwozero, #karl, and #erickson to create this:
package myPkg;
public class CLHUtilities {
private static boolean saying = false;
public static void tracing(boolean b) {
saying = b;
}
/*
* Technique taken from:
* http://stackoverflow.com/questions/282977/which-class-invoked-my-static-method
*/
public static void say(String s) {
if (saying) {
Throwable t = new Throwable();
StackTraceElement[] trace = t.getStackTrace();
String className = trace[1].getClassName();
String whoCalledMe = null;
try {
whoCalledMe = Class.forName(className).getSimpleName();
} catch (Exception e) {
}
System.out.println(whoCalledMe + ": " + s);
}
}
}
which can be used simply as:
import static myPkg.CLHUtilities.*;
:
tracing(true);
:
say("We are here.");
Which suits my needs perfectly.

Alternatives to macro substitution in java

I have a log statement in which I always use this.getClass().getSimpleName()as the 1st parameter.
I would like to put this in some sort of macro constant and use that in all my log statements.
But I learned that Java has no such simple mechanism unlike say C++.
What is the best way to achieve this sort of functionality in Java?
My example log statements (from Android) is as follows..
Log.v(this.getClass().getSimpleName(),"Starting LocIden service...");

Java doesn't have macros but you can make your code much shorter:
Log.v(this, "Starting LocIden service...");
And in the Log class:
public void v(Object object, String s)
{
_v(object.getClass().getSimpleName(), s);
}
Another approach could be to inspect the call stack.

Karthik, most logging tools allow you to specify the format of the output and one of the parameters is the class name, which uses the method Mark mentioned (stack inspection)
For example, in log4j the parameter is %C to reference a class name.

Another approach is to follow what android suggests for its logging functionality.
Log.v(TAG, "Message");
where TAG is a private static final string in your class.

Use a proper logging framework (e.g. slf4j). Each class that logs has its own logger, so there's no need to pass the class name to the log method call.
Logger logger = LoggerFactory.getLogger(this.getClass());
logger.debug("Starting service");
//...
logger.debug("Service started");