NullpointerException in enum Logger - java

I have a class ValueRepository class and want to use a logger in it. The following code always throws a NullPointerException.
public enum ValueRepository {
INSTANCE;
private static final Logger LOGGER = LoggerFactory.getLogger(ValueRepository.class.getName());
private Map<String, Set<String>> key2value;
private Map value2key;
ValueRepository() {
key2value = new HashMap();
value2key = new HashMap();
load("keyValue.txt");
}
public int size() {
return key2value.size();
}
public boolean hasKey(String key) {
return key2value.containsKey(key);
}
public boolean hasValue(String value) {
return value2key.containsKey(value);
}
public Set<String> getValues(String key) {
return key2value.get(key);
}
public String getKey(String value) {
return (String) value2key.get(value);
}
private void load(String filePath) {
BufferedReader br;
try {
br = IOUtils.fileReaderAsResource(filePath);
String line = null;
while ((line = br.readLine()) != null) {
LOGGER.info("test");
line = line.trim();
}
br.close();
} catch (IOException io) {
LOGGER.error("Can't load the file: " + filePath);
io.printStackTrace();
}
}
public static void main(String[] args) {
// do nothing
}
Shouldn't this work?
This question is very different from the link. It's specifically about why it doesn't work in logger in enum.
EDIT:
SLF4J: Class path contains multiple SLF4J bindings.
SLF4J: Found binding in [jar:file:/Users/congmi/.m2/repository/org/apache/logging/log4j/log4j-slf4j-impl/2.6.2/log4j-slf4j-impl-2.6.2.jar!/org/slf4j/impl/StaticLoggerBinder.class]
SLF4J: Found binding in [jar:file:/Users/congmi/.m2/repository/org/slf4j/slf4j-log4j12/1.7.21/slf4j-log4j12-1.7.21.jar!/org/slf4j/impl/StaticLoggerBinder.class]
SLF4J: See http://www.slf4j.org/codes.html#multiple_bindings for an explanation.
SLF4J: Actual binding is of type [org.apache.logging.slf4j.Log4jLoggerFactory]
Exception in thread "main" java.lang.ExceptionInInitializerError
Caused by: java.lang.NullPointerException
at com.qe.repository.ValueRepository.load(ValueRepository.java:56)
at com.qe.repository.ValueRepository.<init>(ValueRepository.java:26)
at com.qe.repository.ValueRepository.<clinit>(ValueRepository.java:14)
Process finished with exit code 1

Because you designed your ValueRepository singleton as an enum
you got this initialization sequence of static constants:
INSTANCE (implicitly calling the constructor)
LOGGER
You need to change this initialization sequence to:
LOGGER
INSTANCE
You can't reach this sequence with enum, because the Java syntax insists
that the enum instances are the very first.
That means, you need to implement your singleton as a normal class, not as an enum.
public class ValueRepository {
private static final Logger LOGGER = LoggerFactory.getLogger(ValueRepository.class.getName());
public static final ValueRepository INSTANCE = new ValueRepository();
// remaining code unchanged
}

Short Answer: In your enum the static LOGGER variable is null until the constructor finishes. There are a few options for you.
Make the logger an instance variable (remove static),
Don't reference LOGGER during construction (throw an exception instead).
Load the data into a static field in a static initializer block, rather during the constructor.
Long Answer: In general, enum static fields will not resolve until the instances are built, whether or not you've got a singleton enum, or multiple enum entries.
That means any time you reference a private static final field that requires another piece of code running (aka - not a string or primitive) during the instance construction, it will fail with a NullPointerException.
See this example in action here
import java.util.Date;
public class HelloWorld{
public static void main(String []args){
System.out.println("Hello World");
final WierdEnum instance = WierdEnum.INSTANCE;
instance.printStuff();
}
static enum WierdEnum {
INSTANCE;
private static final String test = "hello";
private static final Date date = new Date();
WierdEnum() {
printStuff();
}
void printStuff() {
System.out.println("Static string: " + test);
System.out.println("Static date: " + date);
}
}
}
Resolves to:
$java -Xmx128M -Xms16M HelloWorld
Hello World
Static string: hello
Static date: null
Static string: hello
Static date: Mon Apr 16 18:57:27 UTC 2018
The problem is that the class loading order is causing you to ending up with null class variables during the instance construction. This is a different order for an enum than for a class
I suspect you'd like to keep this an enum since you're using it as a singleton pattern and you probably have this pattern elsewhere in your code. You have a few options:
1. Change the logger to an instance rather than class variable by removing static. We don't normally use an instance variable for a logger because it would have a logger for each instance of the object in the system. In this case, there's only one! So it's no problem.
private final Logger LOGGER = LoggerFactory.getLogger(ValueRepository.class);
2. OR Don't use the logger during construction. Instead of logging, throw a new exception if there is a problem reading the file. I suspect that's preferable, since it doesn't look like you can recover from a failed file read.
} catch (IOException io) {
throw new RuntimeException("Can't load the file: " + filePath, io);
}
3. Load the data into static fields in a static initializer block.
private static Map<String, Set<String>> key2value = new HashMap<>();
private static Map value2key = new HashMap();
static {
load("keyValue.txt");
}
private static void load(String filePath) {
...

Related

Make the "LOGGER" logger private static final error is thrown for interface in SonarQube

By default Java Interface doesn't allow private static final members. But in SonarQube, Make the "LOGGER" logger private static final error is thrown for interface.
Any specific reason for this?
Example:
public interface UserPropUtil {
static final Logger LOGGER=Logger.getLogger(UserPropUtil.class.getName());
static String getUserProp(String key, String defaultValue) {
Userprop toReturn=null;
try {
toReturn= getUserProp(key);
} catch (Exception e) {
LOGGER.severe(e.getMessage());
}
return toReturn;
}
}

How to output to file depending on source calling class using log4j

I have a common DAO class with the logger initialized by its name.
I have something like this:
public class QueueDaoImpl implements QueueDao {
private static Logger log = LoggerFactory.getLogger(QueueDaoImpl.class);
#Autowired
private StoredProcedureFactory storedProcedureFactory;
#Override
#Transactional(readOnly = true, value = "transactionManager")
public EnqueueRespVO enqueueMessage(EnqueueMsgReqVO req) throws DAOException {
EnqueueRespVO toResponse;
try {
EnqueueMessageStoredProcedure sp = storedProcedureFactory.getEnqueueMessageSP();
Map<String, String> inParams = BeanUtils.describe(req);
Map<String, Object> out = sp.execute(inParams);
toResponse = new EnqueueRespVO();
toResponse.setErrCode((Integer) out.get(EnqueueMessageStoredProcedure.ERROR_CODE_OUT_PARAM));
toResponse.setErrDescription((String) out.get(EnqueueMessageStoredProcedure.ERROR_DESC_OUT_PARAM));
} catch (DataAccessException e) {
final String msg = String.format("A database error has occurred. Error = ", e);
//log.error("[login] - Ended with an error. ", msg);
throw new DAOException(msg, e);
} catch (IllegalStateException | IllegalAccessException | InvocationTargetException | NoSuchMethodException e) {
final String msg = String.format("A internal error has occurred. Error = ", e);
//log.error("[login] - Ended with an error. ", msg);
throw new DAOException(msg, e);
}
return toResponse;
}
}
Then, I have two classes (posted below), 'RetryCallUssdJob' and 'SendErrorDetail' that use 'QueryDaoImpl' as composed object to do the database logic.
(I'm using Spring to inject the Dao beans)
Example of RetryCallUssdJob class
#Component
public class RetryCallUssdJob {
private static Logger log = LoggerFactory.getLogger(RetryCallUssdJob.class);
#Autowired
private QueueDao queueDao;
public synchronized void execute() {
here i'm using the queueDao instance injected by the spring context
}
}
Example of SendErrorDetail class
public class SendErrorDetailHandlerImpl implements ISendErrorDetailHandler {
private static Logger log = LoggerFactory.getLogger(SendErrorDetailHandlerImpl.class);
#Autowired
private QueueDao queueDaoImpl;
#Override
public BaseRespVO execute(Map<String, Object> params) {
here i'm using the queueDao instance injected by the spring context
}
}
I would like to know how to make output of 'QueryDaoImpl' logger redirected to different log files depending on what calling class is?
Thanks in advance.
This is tricky, I'd do one of two things:
1) Pass in the Logger in on the method call
or
2) Have different marker interfaces for the DAO that have different loggers injected by spring.
1 is easier, 2 is more declarative.

Static Field as Null when mocking Enums with PowerMock

I have written a Thread Pool and I am not able to write the Junits(PowerMock) for that class.
public enum ThreadPool {
INSTANCE;
private static final String THREAD_POOL_SIZE = "threadpool.objectlevel.size";
private static TPropertyReader PROP_READER = new PropertyReader();
private final ExecutorService executorService;
private static final ILogger LOGGER = LoggerFactory
.getLogger(ReportExecutorObjectLevelThreadPool.class.getName());
ThreadPool() {
loadProperties();
int no_of_threads = getThreadPoolSize();
executorService = Executors.newFixedThreadPool(no_of_threads);
}
public void submitTask(Runnable task) {
executorService.execute(task);
}
private static void loadProperties() {
try {
PROP_READER.loadProperties("Dummy");
} catch (final OODSystemException e) {
LOGGER.severe("Loading properties for app failed!");
}
}
private int getThreadPoolSize() {
return Integer.valueOf(PROP_READER
.getProperty(THREAD_POOL_SIZE));
}
}
While Mocking this class I am getting NullPointerException in the line PROP_READER.loadProperties("DUMMY");
My Test Case is:-
PowerMockito.whenNew(PropertyReader.class).withNoArguments().thenReturn(mockPropertyReader);
PowerMockito.doNothing().when( mockPropertyReader,"loadProperties",anyString());
mockStatic(ThreadPool.class);
First you need to set your internal state of your enum as enum is final class
and the instance of an enum will be load on class loading
ThreadPool mockInstance = mock(ThreadPool .class);
Whitebox.setInternalState(ThreadPool.class, "INSTANCE", mockInstance);
then
PowerMockito.mockStatic(ThreadPool .class);
and then mocking
doNothing().when(mockInstance).loadProperties(any(String.class));
do not forget adding the following annotation to the test
#RunWith(PowerMockRunner.class)
#PrepareForTest({ThreadPool.class})
if it still not working you need to see which more member of the class you need to set in the internal state

Java logger that automatically determines caller's class name

public static Logger getLogger() {
final Throwable t = new Throwable();
final StackTraceElement methodCaller = t.getStackTrace()[1];
final Logger logger = Logger.getLogger(methodCaller.getClassName());
logger.setLevel(ResourceManager.LOGLEVEL);
return logger;
}
This method would return a logger that knows the class it's logging for.
Any ideas against it?
Many years later: https://github.com/yanchenko/droidparts/blob/master/droidparts/src/org/droidparts/util/L.java
The MethodHandles class (as of Java 7) includes a Lookup class that, from a static context, can find and return the name of the current class. Consider the following example:
import java.lang.invoke.MethodHandles;
public class Main {
private static final Class clazz = MethodHandles.lookup().lookupClass();
private static final String CLASSNAME = clazz.getSimpleName();
public static void main( String args[] ) {
System.out.println( CLASSNAME );
}
}
When run this produces:
Main
For a logger, you could use:
private static Logger LOGGER =
Logger.getLogger(MethodHandles.lookup().lookupClass().getSimpleName());
Creating a stack trace is a relatively slow operation. Your caller already knows what class and method it is in, so the effort is wasted. This aspect of your solution is inefficient.
Even if you use static class information, you should not fetch the Logger again for each message. From the author of Log4j,Ceki Gülcü:
The most common error in wrapper classes is the invocation of the Logger.getLogger method on each log request. This is guaranteed to wreak havoc on your application's performance. Really!!!
This is the conventional, efficient idiom for getting a Logger is during class initialization:
private static final Logger log = Logger.getLogger(MyClass.class);
Note that this gives you a separate Logger for each type in a hierarchy. If you come up with a method that invokes getClass() on an instance, you will see messages logged by a base type showing up under the subtype's logger. Maybe this is desirable in some cases, but I find it confusing (and I tend to favor composition over inheritance anyway).
Obviously, using the dynamic type via getClass() will require you to obtain the logger at least once per instance, rather than once per class like the recommended idiom using static type information.
I guess it adds a lot of overhead for every class. Every class has to be 'looked up'. You create new Throwable objects to do that... These throwables don't come for free.
We actually have something quite similar in a LogUtils class. Yes, it's kind of icky, but the advantages are worth it as far as I'm concerned. We wanted to make sure we didn't have any overhead from it being repeatedly called though, so ours (somewhat hackily) ensures that it can ONLY be called from a static initializer context, a la:
private static final Logger LOG = LogUtils.loggerForThisClass();
It will fail if it's invoked from a normal method, or from an instance initializer (i.e. if the 'static' was left off above) to reduce the risk of performance overhead. The method is:
public static Logger loggerForThisClass() {
// We use the third stack element; second is this method, first is .getStackTrace()
StackTraceElement myCaller = Thread.currentThread().getStackTrace()[2];
Assert.equal("<clinit>", myCaller.getMethodName());
return Logger.getLogger(myCaller.getClassName());
}
Anyone who asks what advantage does this have over
= Logger.getLogger(MyClass.class);
has probably never had to deal with someone who copies and pastes that line from somewhere else and forgets to change the class name, leaving you dealing with a class which sends all its stuff to another logger.
Assuming you are keeping static refs to the loggers, here's a standalone static singleton:
public class LoggerUtils extends SecurityManager
{
public static Logger getLogger()
{
String className = new LoggerUtils().getClassName();
Logger logger = Logger.getLogger(className);
return logger;
}
private String getClassName()
{
return getClassContext()[2].getName();
}
}
Usage is nice and clean:
Logger logger = LoggerUtils.getLogger();
For every class that you use this with, you're going to have to look up the Logger anyway, so you might as well just use a static Logger in those classes.
private static final Logger logger = Logger.getLogger(MyClass.class.getName());
Then you just reference that logger when you need to do your log messages. Your method does the same thing that the static Log4J Logger does already so why reinvent the wheel?
A good alternative is to use (one of) the lombok logs annotations :
https://projectlombok.org/features/Log.html
It generate the corresponding log statement with the current class.
Then the best thing is mix of two .
public class LoggerUtil {
public static Level level=Level.ALL;
public static java.util.logging.Logger getLogger() {
final Throwable t = new Throwable();
final StackTraceElement methodCaller = t.getStackTrace()[1];
final java.util.logging.Logger logger = java.util.logging.Logger.getLogger(methodCaller.getClassName());
logger.setLevel(level);
return logger;
}
}
And then in every class:
private static final Logger LOG = LoggerUtil.getLogger();
in code :
LOG.fine("debug that !...");
You get static logger that you can just copy&paste in every class and with no overhead ...
Alaa
From reading through all the other feedback on this site, I created the following for use with Log4j:
package com.edsdev.testapp.util;
import java.util.concurrent.ConcurrentHashMap;
import org.apache.log4j.Level;
import org.apache.log4j.Priority;
public class Logger extends SecurityManager {
private static ConcurrentHashMap<String, org.apache.log4j.Logger> loggerMap = new ConcurrentHashMap<String, org.apache.log4j.Logger>();
public static org.apache.log4j.Logger getLog() {
String className = new Logger().getClassName();
if (!loggerMap.containsKey(className)) {
loggerMap.put(className, org.apache.log4j.Logger.getLogger(className));
}
return loggerMap.get(className);
}
public String getClassName() {
return getClassContext()[3].getName();
}
public static void trace(Object message) {
getLog().trace(message);
}
public static void trace(Object message, Throwable t) {
getLog().trace(message, t);
}
public static boolean isTraceEnabled() {
return getLog().isTraceEnabled();
}
public static void debug(Object message) {
getLog().debug(message);
}
public static void debug(Object message, Throwable t) {
getLog().debug(message, t);
}
public static void error(Object message) {
getLog().error(message);
}
public static void error(Object message, Throwable t) {
getLog().error(message, t);
}
public static void fatal(Object message) {
getLog().fatal(message);
}
public static void fatal(Object message, Throwable t) {
getLog().fatal(message, t);
}
public static void info(Object message) {
getLog().info(message);
}
public static void info(Object message, Throwable t) {
getLog().info(message, t);
}
public static boolean isDebugEnabled() {
return getLog().isDebugEnabled();
}
public static boolean isEnabledFor(Priority level) {
return getLog().isEnabledFor(level);
}
public static boolean isInfoEnabled() {
return getLog().isInfoEnabled();
}
public static void setLevel(Level level) {
getLog().setLevel(level);
}
public static void warn(Object message) {
getLog().warn(message);
}
public static void warn(Object message, Throwable t) {
getLog().warn(message, t);
}
}
Now in your code all you need is
Logger.debug("This is a test");
or
Logger.error("Look what happened Ma!", e);
If you need more exposure to log4j methods, just delegate them from the Logger class listed above.
You could of course just use Log4J with the appropriate pattern layout:
For example, for the class name "org.apache.xyz.SomeClass", the pattern %C{1} will output "SomeClass".
http://logging.apache.org/log4j/1.2/apidocs/org/apache/log4j/PatternLayout.html
I prefer creating a (static) Logger for each class (with it's explicit class name). I than use the logger as is.
You don't need to create a new Throwable object. You can just call
Thread.currentThread().getStackTrace()[1]
I just have the following line at the beginning of most of my classes.
private static final Logger log =
LoggerFactory.getLogger(new Throwable().getStackTrace()[0].getClassName());
yes there is some overhead the very first time an object of that class is created, but I work mostly in webapps, so adding microseconds onto a 20 second startup isn't really a problem.
Google Flogger logging API supports this e.g.
private static final FluentLogger logger = FluentLogger.forEnclosingClass();
See https://github.com/google/flogger for more details.
A nice way to do this from Java 7 onwards:
private static final Logger logger = LoggerFactory.getLogger(MethodHandles.lookup().lookupClass());
The logger can be static and that fine.
Here its using the SLF4J API
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
But in principal can be used with any logging framework. If the logger needs a string argument add toString()
Simple and trivial OLD SCHOOL:
Just create your own class and pass there class name, method name + comment (if class /method changed they're refactored automatically Shift+F6)
public class MyLogs {
public static void LOG(String theClass, String theMethod, String theComment) {
Log.d("MY_TAG", "class: " + theClass + " meth : " + theMethod + " comm : " + theComment);
}
}
and just use it anywhere in the app (no context required, no initialzation, no extra libs and no look up) - can be used for any programing language!
MyLogs.LOG("MainActivity", "onCreate", "Hello world");
this will print in your console:
MY_TAG class: MainActivity meth: onCreate comm: Hello world
Why not?
public static Logger getLogger(Object o) {
final Logger logger = Logger.getLogger(o.getClass());
logger.setLevel(ResourceManager.LOGLEVEL);
return logger;
}
And then when you need a logger for a class:
getLogger(this).debug("Some log message")
This mechanism puts in a lot of extra effort at runtime.
If you use Eclipse as your IDE, consider using Log4e. This handy plugin will generate logger declarations for you using your favourite logging framework. A fraction more effort at coding time, but much less work at runtime.
Unless you really need your Logger to be static, you could use
final Logger logger = LoggerFactory.getLogger(getClass());
Please see my static getLogger() implementation (use same "sun.*" magic on JDK 7 as default java Logger doit)
note static logging methods (with static import) without ugly log property...
import static my.pakg.Logger.*;
And their speed is equivalent to native Java implementation (checked with 1 million of log traces)
package my.pkg;
import java.text.MessageFormat;
import java.util.Arrays;
import java.util.IllegalFormatException;
import java.util.logging.Level;
import java.util.logging.LogRecord;
import sun.misc.JavaLangAccess;
import sun.misc.SharedSecrets;
public class Logger {
static final int CLASS_NAME = 0;
static final int METHOD_NAME = 1;
// Private method to infer the caller's class and method names
protected static String[] getClassName() {
JavaLangAccess access = SharedSecrets.getJavaLangAccess();
Throwable throwable = new Throwable();
int depth = access.getStackTraceDepth(throwable);
boolean lookingForLogger = true;
for (int i = 0; i < depth; i++) {
// Calling getStackTraceElement directly prevents the VM
// from paying the cost of building the entire stack frame.
StackTraceElement frame = access.getStackTraceElement(throwable, i);
String cname = frame.getClassName();
boolean isLoggerImpl = isLoggerImplFrame(cname);
if (lookingForLogger) {
// Skip all frames until we have found the first logger frame.
if (isLoggerImpl) {
lookingForLogger = false;
}
} else {
if (!isLoggerImpl) {
// skip reflection call
if (!cname.startsWith("java.lang.reflect.") && !cname.startsWith("sun.reflect.")) {
// We've found the relevant frame.
return new String[] {cname, frame.getMethodName()};
}
}
}
}
return new String[] {};
// We haven't found a suitable frame, so just punt. This is
// OK as we are only committed to making a "best effort" here.
}
protected static String[] getClassNameJDK5() {
// Get the stack trace.
StackTraceElement stack[] = (new Throwable()).getStackTrace();
// First, search back to a method in the Logger class.
int ix = 0;
while (ix < stack.length) {
StackTraceElement frame = stack[ix];
String cname = frame.getClassName();
if (isLoggerImplFrame(cname)) {
break;
}
ix++;
}
// Now search for the first frame before the "Logger" class.
while (ix < stack.length) {
StackTraceElement frame = stack[ix];
String cname = frame.getClassName();
if (isLoggerImplFrame(cname)) {
// We've found the relevant frame.
return new String[] {cname, frame.getMethodName()};
}
ix++;
}
return new String[] {};
// We haven't found a suitable frame, so just punt. This is
// OK as we are only committed to making a "best effort" here.
}
private static boolean isLoggerImplFrame(String cname) {
// the log record could be created for a platform logger
return (
cname.equals("my.package.Logger") ||
cname.equals("java.util.logging.Logger") ||
cname.startsWith("java.util.logging.LoggingProxyImpl") ||
cname.startsWith("sun.util.logging."));
}
protected static java.util.logging.Logger getLogger(String name) {
return java.util.logging.Logger.getLogger(name);
}
protected static boolean log(Level level, String msg, Object... args) {
return log(level, null, msg, args);
}
protected static boolean log(Level level, Throwable thrown, String msg, Object... args) {
String[] values = getClassName();
java.util.logging.Logger log = getLogger(values[CLASS_NAME]);
if (level != null && log.isLoggable(level)) {
if (msg != null) {
log.log(getRecord(level, thrown, values[CLASS_NAME], values[METHOD_NAME], msg, args));
}
return true;
}
return false;
}
protected static LogRecord getRecord(Level level, Throwable thrown, String className, String methodName, String msg, Object... args) {
LogRecord record = new LogRecord(level, format(msg, args));
record.setSourceClassName(className);
record.setSourceMethodName(methodName);
if (thrown != null) {
record.setThrown(thrown);
}
return record;
}
private static String format(String msg, Object... args) {
if (msg == null || args == null || args.length == 0) {
return msg;
} else if (msg.indexOf('%') >= 0) {
try {
return String.format(msg, args);
} catch (IllegalFormatException esc) {
// none
}
} else if (msg.indexOf('{') >= 0) {
try {
return MessageFormat.format(msg, args);
} catch (IllegalArgumentException exc) {
// none
}
}
if (args.length == 1) {
Object param = args[0];
if (param != null && param.getClass().isArray()) {
return msg + Arrays.toString((Object[]) param);
} else if (param instanceof Throwable){
return msg;
} else {
return msg + param;
}
} else {
return msg + Arrays.toString(args);
}
}
public static void severe(String msg, Object... args) {
log(Level.SEVERE, msg, args);
}
public static void warning(String msg, Object... args) {
log(Level.WARNING, msg, args);
}
public static void info(Throwable thrown, String format, Object... args) {
log(Level.INFO, thrown, format, args);
}
public static void warning(Throwable thrown, String format, Object... args) {
log(Level.WARNING, thrown, format, args);
}
public static void warning(Throwable thrown) {
log(Level.WARNING, thrown, thrown.getMessage());
}
public static void severe(Throwable thrown, String format, Object... args) {
log(Level.SEVERE, thrown, format, args);
}
public static void severe(Throwable thrown) {
log(Level.SEVERE, thrown, thrown.getMessage());
}
public static void info(String msg, Object... args) {
log(Level.INFO, msg, args);
}
public static void fine(String msg, Object... args) {
log(Level.FINE, msg, args);
}
public static void finer(String msg, Object... args) {
log(Level.FINER, msg, args);
}
public static void finest(String msg, Object... args) {
log(Level.FINEST, msg, args);
}
public static boolean isLoggableFinest() {
return isLoggable(Level.FINEST);
}
public static boolean isLoggableFiner() {
return isLoggable(Level.FINER);
}
public static boolean isLoggableFine() {
return isLoggable(Level.FINE);
}
public static boolean isLoggableInfo() {
return isLoggable(Level.INFO);
}
public static boolean isLoggableWarning() {
return isLoggable(Level.WARNING);
}
public static boolean isLoggableSevere() {
return isLoggable(Level.SEVERE);
}
private static boolean isLoggable(Level level) {
return log(level, null);
}
}
Take a look at Logger class from jcabi-log. It does exactly what you're looking for, providing a collection of static methods. You don't need to embed loggers into classes any more:
import com.jcabi.log.Logger;
class Foo {
public void bar() {
Logger.info(this, "doing something...");
}
}
Logger sends all logs to SLF4J, which you can redirect to any other logging facility, in runtime.

Using different classloaders for different JUnit tests?

I have a Singleton/Factory object that I'd like to write a JUnit test for. The Factory method decides which implementing class to instantiate based upon a classname in a properties file on the classpath. If no properties file is found, or the properties file does not contain the classname key, then the class will instantiate a default implementing class.
Since the factory keeps a static instance of the Singleton to use once it has been instantiated, to be able to test the "failover" logic in the Factory method I would need to run each test method in a different classloader.
Is there any way with JUnit (or with another unit testing package) to do this?
edit: here is some of the Factory code that is in use:
private static MyClass myClassImpl = instantiateMyClass();
private static MyClass instantiateMyClass() {
MyClass newMyClass = null;
String className = null;
try {
Properties props = getProperties();
className = props.getProperty(PROPERTY_CLASSNAME_KEY);
if (className == null) {
log.warn("instantiateMyClass: Property [" + PROPERTY_CLASSNAME_KEY
+ "] not found in properties, using default MyClass class [" + DEFAULT_CLASSNAME + "]");
className = DEFAULT_CLASSNAME;
}
Class MyClassClass = Class.forName(className);
Object MyClassObj = MyClassClass.newInstance();
if (MyClassObj instanceof MyClass) {
newMyClass = (MyClass) MyClassObj;
}
}
catch (...) {
...
}
return newMyClass;
}
private static Properties getProperties() throws IOException {
Properties props = new Properties();
InputStream stream = Thread.currentThread().getContextClassLoader().getResourceAsStream(PROPERTIES_FILENAME);
if (stream != null) {
props.load(stream);
}
else {
log.error("getProperties: could not load properties file [" + PROPERTIES_FILENAME + "] from classpath, file not found");
}
return props;
}
This question might be old but since this was the nearest answer I found when I had this problem I though I'd describe my solution.
Using JUnit 4
Split your tests up so that there is one test method per class (this solution only changes classloaders between classes, not between methods as the parent runner gathers all the methods once per class)
Add the #RunWith(SeparateClassloaderTestRunner.class) annotation to your test classes.
Create the SeparateClassloaderTestRunner to look like this:
public class SeparateClassloaderTestRunner extends BlockJUnit4ClassRunner {
public SeparateClassloaderTestRunner(Class<?> clazz) throws InitializationError {
super(getFromTestClassloader(clazz));
}
private static Class<?> getFromTestClassloader(Class<?> clazz) throws InitializationError {
try {
ClassLoader testClassLoader = new TestClassLoader();
return Class.forName(clazz.getName(), true, testClassLoader);
} catch (ClassNotFoundException e) {
throw new InitializationError(e);
}
}
public static class TestClassLoader extends URLClassLoader {
public TestClassLoader() {
super(((URLClassLoader)getSystemClassLoader()).getURLs());
}
#Override
public Class<?> loadClass(String name) throws ClassNotFoundException {
if (name.startsWith("org.mypackages.")) {
return super.findClass(name);
}
return super.loadClass(name);
}
}
}
Note I had to do this to test code running in a legacy framework which I couldn't change. Given the choice I'd reduce the use of statics and/or put test hooks in to allow the system to be reset. It may not be pretty but it allows me to test an awful lot of code that would be difficult otherwise.
Also this solution breaks anything else that relies on classloading tricks such as Mockito.
When I run into these sort of situations I prefer to use what is a bit of a hack. I might instead expose a protected method such as reinitialize(), then invoke this from the test to effectively set the factory back to its initial state. This method only exists for the test cases, and I document it as such.
It is a bit of a hack, but it's a lot easier than other options and you won't need a 3rd party lib to do it (though if you prefer a cleaner solution, there probably are some kind of 3rd party tools out there you could use).
You can use Reflection to set myClassImpl by calling instantiateMyClass() again. Take a look at this answer to see example patterns for playing around with private methods and variables.
If executing Junit via the Ant task you can set fork=true to execute every class of tests in it's own JVM. Also put each test method in its own class and they will each load and initialise their own version of MyClass. It's extreme but very effective.
Below you can find a sample that does not need a separate JUnit test runner and works also with classloading tricks such as Mockito.
package com.mycompany.app;
import static org.junit.Assert.assertEquals;
import static org.mockito.Mockito.mock;
import static org.mockito.Mockito.verify;
import java.net.URLClassLoader;
import org.junit.Test;
public class ApplicationInSeparateClassLoaderTest {
#Test
public void testApplicationInSeparateClassLoader1() throws Exception {
testApplicationInSeparateClassLoader();
}
#Test
public void testApplicationInSeparateClassLoader2() throws Exception {
testApplicationInSeparateClassLoader();
}
private void testApplicationInSeparateClassLoader() throws Exception {
//run application code in separate class loader in order to isolate static state between test runs
Runnable runnable = mock(Runnable.class);
//set up your mock object expectations here, if needed
InterfaceToApplicationDependentCode tester = makeCodeToRunInSeparateClassLoader(
"com.mycompany.app", InterfaceToApplicationDependentCode.class, CodeToRunInApplicationClassLoader.class);
//if you want to try the code without class loader isolation, comment out above line and comment in the line below
//CodeToRunInApplicationClassLoader tester = new CodeToRunInApplicationClassLoaderImpl();
tester.testTheCode(runnable);
verify(runnable).run();
assertEquals("should be one invocation!", 1, tester.getNumOfInvocations());
}
/**
* Create a new class loader for loading application-dependent code and return an instance of that.
*/
#SuppressWarnings("unchecked")
private <I, T> I makeCodeToRunInSeparateClassLoader(
String packageName, Class<I> testCodeInterfaceClass, Class<T> testCodeImplClass) throws Exception {
TestApplicationClassLoader cl = new TestApplicationClassLoader(
packageName, getClass(), testCodeInterfaceClass);
Class<?> testerClass = cl.loadClass(testCodeImplClass.getName());
return (I) testerClass.newInstance();
}
/**
* Bridge interface, implemented by code that should be run in application class loader.
* This interface is loaded by the same class loader as the unit test class, so
* we can call the application-dependent code without need for reflection.
*/
public static interface InterfaceToApplicationDependentCode {
void testTheCode(Runnable run);
int getNumOfInvocations();
}
/**
* Test-specific code to call application-dependent code. This class is loaded by
* the same class loader as the application code.
*/
public static class CodeToRunInApplicationClassLoader implements InterfaceToApplicationDependentCode {
private static int numOfInvocations = 0;
#Override
public void testTheCode(Runnable runnable) {
numOfInvocations++;
runnable.run();
}
#Override
public int getNumOfInvocations() {
return numOfInvocations;
}
}
/**
* Loads application classes in separate class loader from test classes.
*/
private static class TestApplicationClassLoader extends URLClassLoader {
private final String appPackage;
private final String mainTestClassName;
private final String[] testSupportClassNames;
public TestApplicationClassLoader(String appPackage, Class<?> mainTestClass, Class<?>... testSupportClasses) {
super(((URLClassLoader) getSystemClassLoader()).getURLs());
this.appPackage = appPackage;
this.mainTestClassName = mainTestClass.getName();
this.testSupportClassNames = convertClassesToStrings(testSupportClasses);
}
private String[] convertClassesToStrings(Class<?>[] classes) {
String[] results = new String[classes.length];
for (int i = 0; i < classes.length; i++) {
results[i] = classes[i].getName();
}
return results;
}
#Override
public Class<?> loadClass(String className) throws ClassNotFoundException {
if (isApplicationClass(className)) {
//look for class only in local class loader
return super.findClass(className);
}
//look for class in parent class loader first and only then in local class loader
return super.loadClass(className);
}
private boolean isApplicationClass(String className) {
if (mainTestClassName.equals(className)) {
return false;
}
for (int i = 0; i < testSupportClassNames.length; i++) {
if (testSupportClassNames[i].equals(className)) {
return false;
}
}
return className.startsWith(appPackage);
}
}
}

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