How to use log4j to see into Jersey

Question

I'm new to log4j and am trying to use it to better understand why my resource is providing a 415 Media Type Not Supported header.

I'm using the following:

log4j.rootCategory=WARN, stdout

log4j.appender.stdout=org.apache.log4j.ConsoleAppender
log4j.appender.stdout.layout=org.apache.log4j.PatternLayout
log4j.appender.stdout.layout.ConversionPattern=%d{ABSOLUTE} %5p %t %c:%L - %m%n

log4j.category.com.sun.jersey=DEBUG,stdout

This seems like it should work but I'm showing nothing in the console about the POST reaching this application. I know it is reaching the application because if I turn the application off, the POSTer throws a "connection refused" when trying to POST.

Answer 1

I'm afraid it's not as straightforward as adding the Jersey packages to your Log4J config. Jersey does not use Log4J internally; instead it uses Java logging.

If you prefer to work with Log4J then your option is to configure Java logging to use the SLF4JBridgeHandler as a logging handler.

Typically this is done by specifying a logging properties file via JVM property, and adding handlers to the properties file, like so:

1. specify the logging properties file

   -Djava.util.logging.config.file=/path/to/logging.properties

2. add the SLF4JBridgeHandler as a logging handler in the logging.properties file

   handlers=org.slf4j.bridge.SLF4JBridgeHandler

SLF4J can then bind to Log4J, and you can then use your log4j.properties as usual to specify the logging level for Jersey classes.

As an aside, my advice -- if you're just doing this for quick-and-dirty debugging -- is to either:

1. attach a debugger to your application (assuming you have the application source code);

2. or work with Java logging directly. To configure Java logging to output to a file, add the following to your logging.properties file as specified earlier --

   com.sun.jersey.level=DEBUG
   com.sun.jersey.handlers=java.util.logging.FileHandler
   java.util.logging.FileHandler.pattern=/path/to/debugging.log
   java.util.logging.FileHandler.formatter=java.util.logging.SimpleFormatter

Answer 2

You can use JUL to SLF4J Bridge for this first add it to your classpath. You can use this if you are using maven:

<dependency>
    <groupId>org.slf4j</groupId>
    <artifactId>jul-to-slf4j</artifactId>
    <version>1.7.5</version>
</dependency>

Add those lines to a static initializer block or in your main method:

LogManager.getLogManager().reset();
SLF4JBridgeHandler.install();

Now you can control the jersey logs from your log4j.properties file:

log4j.category.org.glassfish.jersey=WARN,stdout