记录Java的注释

Question

是否有任何库允许通过添加注释来记录变量,例如:

@Log
String someValueToLog = someMethod(); 
@Log(level="debug",prefix="Here's the value=")
String someValueToLogAgain = someMethod(); 

该功能类似于在代码中添加此行:

log.info(someValueToLog);
log.debug("Here's the value="+someValueToLogAgain);

Answer 1

I have created a project called log-weaver, which introduces a number of @LogXXX statements.
When you compile a project, that uses one of these annotations, Log-statements are weaves into the bytecocde.
Example source code:

@LogEnteringAndExiting(value={"arg1", "this"})
public String execute(String arg1) {
    /*Some logic*/
return "done";
}

The source code will remain as is, but the byte code will look as if the source code had been written like this:

private static final Logger comGithubHervian_LOGGER = LoggingHelper.getLogger(ClassWithLogAnnotatedMethods.LogAround_log1ArgumentAndThis.class);
private static final String = comGithubHervian_CLASSNAME = ClassWithLogAnnotatedMethods.LogAround_log1ArgumentAndThis.class.getName();

public String execute(String arg1) {
    if (LoggingHelper.isEntryExitTraceEnabled((Logger)comGithubHervian_LOGGER)) {
        comGithubHervian_LOGGER.entering(comGithubHervian_CLASSNAME, "execute", new Object[]{arg1, this});
    }
    /*Some logic*/
    String string = "done";
    if (LoggingHelper.isEntryExitTraceEnabled((Logger)comGithubHervian_LOGGER)) {
        comGithubHervian_LOGGER.exiting(comGithubHervian_CLASSNAME, "execute", string);
    }
    return string;
}

In the code above the LoggingHelper is a special class from IBM's WebpShere Commerce for which this proof of concept was developed.

The idea is to simplify the source code by removing trivial statements, in this case logging.
The overall logic is as follows:

1. An AbstractProcessor detects the usage of one the log annotations, and creates some useful data structure, to hold information about the method name, arguments etc.
2. The AbstractProcessor registers a TaskListener at the compiler (Javac).
3. The TaskListener uses Javassist to weave log statements into the byte code of the given method/class.

Please be aware that the current project is designed for use with IBM's WebSphere Commerce, but you could easily adjust it, such as to weave log-statements of your own choosing into the code.