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Non-Spring lightweight AOP without xml config for weaving annotations to methods

Need to run before and after methods on some annotations.
Not using spring, no xml. Is it possible to have some kind of AOP engine that I set from main() so that it can be invoked whenever needed? It's also OK for me to put in a method to manually call an evaluation method.
Example:
public void doThis(#RequiredSecurityRole("admin") user){
doAOPStuff();
}
before() get from the db and check if user is admin, throws Exception if it's not admin.
after() log into db the action.
How to achieve this?

You can do this yourself using the java.lang.reflex.Proxy class. It does require that the code you're proxying be defined in an interface.
import static java.lang.annotation.RetentionPolicy.RUNTIME;
import java.lang.annotation.Retention;
import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;
public class DoItYourAop {
public static void main(String[] args) {
SaysHello saysHello = new SaysHelloImpl();
InvocationHandler logger = new LoggingProxy(saysHello);
SaysHello proxy = (SaysHello) Proxy.newProxyInstance(SaysHello.class.getClassLoader(),
new Class[]{SaysHello.class}, logger);
proxy.sayHello();
}
public interface SaysHello {
void sayHello();
void sayGoodbye();
}
public static class SaysHelloImpl implements SaysHello {
#Log
#Override
public void sayHello() {
System.out.println("Says Hello");
}
#Override
public void sayGoodbye() {
System.out.println("Says Goodbye");
}
}
#Retention(RUNTIME)
#interface Log {
}
public static class LoggingProxy implements InvocationHandler {
private final Object proxied;
public LoggingProxy(Object proxied) {
this.proxied = proxied;
}
#Override
public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
Method proxiedMethod = proxied.getClass().getMethod(method.getName(), method.getParameterTypes());
boolean log = proxiedMethod.isAnnotationPresent(Log.class);
if (log) {
System.out.println("Before");
}
Object result = method.invoke(proxied, args);
if (log) {
System.out.println("After");
}
return result;
}
}
}

How is it possible to communicate between two classes in Java using an interface?

Hi ive been reading on some similar topics here but none of them answer my question. Some say you cant even do this which is not a good thing since I cant finnish my course in that case.
Heres som simple code. Think of each block as a separate class.
public interface Interface {
void printMessage(String meddelande);
}
public class Model implements Interface {
String message = "hej!";
public static void main(String[] args) {
Model model1 = new Model();
View view1 = new View();
model1.printMessage(model1.message); //Ska jag anropa funktionen såhär ens?
}
public void printMessage(String str) {
}
}
public class View implements Interface {
printMessage(String str) {
}
}
So, how is it now possible to tel the view to print this string from the model class without the classes knowing about each other? Its not allowed to send a reference of the model-objekt to the view-object. ; (

Define an Interface:
public interface MyInterface {
void printMessage(String str);
}
Define a class that can trigger the notification:
public class ClassNotifier {
MyInterface mInterface;
public ClassNotifier(MyInterface mInterface) {
this.mInterface = mInterface;
}
public void triggerTheMsg(String msg) {
if (mInterface != null) {
mInterface.printMessage(msg);
}
}
}
Define a class that will be informed:
public class InformedClass implements MyInterface {
public static void main(String[] args) throws Exception {
InformedClass c = new InformedClass();
ClassNotifier cn = new ClassNotifier(c);
}
#Override
public void printMessage(String newMsg) {
System.out.println("A new msg is here: " + newMsg);
}
}
How does it works?:
this is named a callback parttern, the class ClassNotifier has a reference to the interface MyInterface, which is impl. by Informed class to, so every time the ClassNotifier calls the method printMessage, the method printMessage in the class Informed will be triggered too.

I advice you to use dependency injection, for example:
public class Model {
String message = "hej!";
Interface printer;
public void Model(Interface printer) {
printer = printer;
}
public static void main(String[] args) {
Model model1 = new Model(new View());
model1.printMessage(model1.message);
}
public void printMessage(String str) {
printer.printMessage(str);
}
}

ThreadWeaver always throws IllegalArgumentException

I am trying to use Google ThreadWeaver to write a unit test for concurrent code. No matter what I do, I will get an IllegalArgumentException. I am still working with an example, but even that does not work. This is what I tried:
public class ExampleTest {
public static class ExampleMain implements MainRunnable<Example> {
private Example example;
#Override
public Class<Example> getClassUnderTest() {
return Example.class;
}
#Override
public String getMethodName() {
return null;
}
#Override
public Method getMethod() throws NoSuchMethodException {
return null;
}
#Override
public void initialize() throws Exception {
example = new Example();
}
#Override
public Example getMainObject() {
return example;
}
#Override
public void terminate() throws Exception {
}
#Override
public void run() throws Exception {
example.test("second");
}
}
public static class ExampleSecondary implements SecondaryRunnable<Example, ExampleMain> {
private ExampleMain exampleMain;
#Override
public void initialize(ExampleMain main) throws Exception {
exampleMain = main;
}
#Override
public void terminate() throws Exception {
}
#Override
public boolean canBlock() {
return false;
}
#Override
public void run() throws Exception {
exampleMain.getMainObject().test("main");
}
}
public static class Example {
private List<String> list = new ArrayList<String>();
public String test(String s) {
System.out.println("1" + s);
list.add(s);
System.out.println("2" + s);
return list.get(0);
}
}
#Test
public void testThreadWeaver() throws Exception {
ClassInstrumentation instrumentation = Instrumentation.getClassInstrumentation(Example.class);
Method tested = Example.class.getDeclaredMethod("test", String.class);
Method breakpoint = List.class.getDeclaredMethod("add", Object.class);
CodePosition codePosition = instrumentation.afterCall(tested, breakpoint);
InterleavedRunner.interleave(new ExampleMain(), new ExampleSecondary(), Arrays.asList(codePosition)).throwExceptionsIfAny();
}
}
The stack trace says:
java.lang.IllegalArgumentException: Class Example is not instrumented
at
com.google.testing.threadtester.CallLoggerFactory.getClassInstrumentation(CallLoggerFactory.java:108)
at
com.google.testing.threadtester.Instrumentation.getClassInstrumentation(Instrumentation.java:65)
at MyTest.testThreadWeaver(MyTest.java:92
I followed the instructions at the official Google code webpage, but it does not seem to work. Any ideas?

ThreadWeaver needs to instrument your classes in order to add breakpoints to your methods. Therefore, you cannot run the tests with JUnit directly but you must run your test from a specific test runner. For your case this would be ThreadedTestRunner. The actual test methods must then be annotated with #ThreadedTest instead of #Test. This should work:
#Test
public void startTest() throws Exception {
new ThreadedTestRunner().runTests(getClass(), Example.class);
}
#ThreadedTest
public void testThreadWeaver() throws Exception {
// here comes your test
}

How create log4j wrap and get correct logs

I have multithreaded application and i want add some text information in every log message
I create factory and extend class, it works fine
...
protected Logger logger = Logger.getLogger("Test", new MyLog4JFactory());
...
import org.apache.log4j.Logger;
import org.apache.log4j.spi.LoggerFactory;
public class MyLog4JFactory implements LoggerFactory{
#Override
public Logger makeNewLoggerInstance(String arg0) {
return new MyLogger(arg0);
}
}
import org.apache.log4j.Logger;
public class MyLogger extends Logger{
protected MyLogger(String name) {
super(name);
}
private String getMessage(Object msg){
StringBuffer sb = new StringBuffer();
return sb.append(msg).append(" ").append("My text").toString();
}
#Override
public void debug(Object message) {
super.debug(getMessage(message));
}
#Override
public void error(Object message) {
super.error(getMessage(message));
}
#Override
public void fatal(Object message) {
super.fatal(getMessage(message));
}
#Override
public void info(Object message) {
super.info(getMessage(message));
}
#Override
public void warn(Object message) {
super.warn(getMessage(message));
}
}
but! in the logs I see the wrapper class
all logs print as
2011-09-08 10:45:49,359 DEBUG MyLogger (35) - Test1 My text
What should I do to the log file shows a classes (with line number) calls my logger?

I know this is an old question, but I would like to share a nice solution I found:
Add FQCN to your class,
call Logger.log method and pass it your FQCN
like so:
public class MyLogger extends Logger{
private static String FQCN = MyLogger.class.getName();
...
#Override
public void debug(Object message) {
super.log(FQCN, org.apache.log4j.Level.DEBUG,message, null);
}
#Override
public void debug(Object message,Throwable t) {
super.log(FQCN, org.apache.log4j.Level.DEBUG,message, t);
}
}
(same will work for creating a wrapper...)

In your log4j.properties file, remove the %l specifier from the line that looks something like this:
log4j.appender.A1.layout.ConversionPattern=<...>
ConversionPattern could be PatternLayout or something else. This will prevent the fully qualified calling class name and line number from being displayed.
More information on the specifiers can be found here.

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.