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Archive for the ‘Frameworks’ Category

Unified (as much as possible) Logging Using SLF4J

with 7 comments

Integrating, integrating, integrating. That’s what we do in Java enterprise development. Persisting objects with Hibernate wrapped by JPA using C3Po (or JTA?) (or MongoDB over Morphia?), processed with JBMP, created by JAXB (jackson-json?) from JAX-RS scheduled by Quartz … (a few dozen frameworks later) … all this glued with Spring (or Guice?) deployed on Jetty (or Tomcat, JBoss, Resin?) into cluster by Terracotta (or Hadoop, GigaSpaces, JBoss cache, Infinispam?). Ah, and all this built using Maven Gradle with Artifactory on Jenkins. I sure forgot ½ of the frameworks we constantly use.

Generally we don’t mind much about the internals of the frameworks we use (as long as they are good) – the whole encapsulation stuff is the last undoubted good thing. But except for the API (part of which is the configuration) frameworks have another user-facing end – the logging. When we build a system we want it to behave as one system – single configuration from one end, and single log from another (break it to different files, if you wish, but it should still be a unified logging system).

The reality is that there is no standard de-facto for logging. The standard de-jure – JUL, is not very popular because of its lack of functionality (compared to alternatives) and its suboptimal performance. And then there is Log4J, which almost became standard, but did not. And there is logback, which is a Log4J trashover, and there are facades (JCL and SLF4J), which try to unite all this zoo, and some others, which you have probably never heard of, like syslog4j*, logging framework by the Object Guy, jLo, MonoLog, Lumberjack, Houston, JTraceDump, qflog, LN2, TracingClassLoader, SMTPHandler, Log4Ant, Simple Log, Log Bridge, Craftsman Spy, Pencil, JDLabAgent, Trace Log, JDBC Logger, LimpidLog and Microlog.

Let it be, you’d say – why not have many logging tools, which are good and diverse! Well, the problem, as I’ve already mentioned, is that they leak out of the frameworks. Their diverse configuration leaks from one end, while their diverse output from another. Spring uses Log4J over JCL. So does Hibernate. Jetty uses Logback over SLF4J. Some (like Terracotta modules) use plain Log4J, Jersey uses JUL.  This means we end up with 5 separate configurations (Log4J, SLF4J, Logback, JCL and JUL) and 3 different types of log files (Log4j, Logback and JUL). What a system!

To make the long story short – How can we achieve the desired consolidation? Clearly, we need a facade. There are two most commonly used – SLF4J and JCL. JCL is known for its classloader hell, SLF4J is newer, better performing, smarter, simplier to use and generally provides better quality for the same buck (well, no buck – both are open source, of course), so we’ll stick to it. SLF4J is an adapter – thin layer of API to and from different logging implementations. Yap, both ways. It means with SLF4J we can use JUL API on top and log using Log4J in the bottom!

First we need to pick an actual logger. Log4j was considered the best choice up until recently (2006) when Ceki Gülcü decided he needed a fresh start and rewrote from scratch a new Java logging framework, just better than log4j, called Logback. We can give it a try as our underlying logging implementation (we can switch in a moment, as we are using  good facade, remember?).

So, here’s what we have to do:

    1. Establish our own good logging:
        1. Add Logback to our classpath
        2. Add SLF4J API to our classpath

      Done here. Now our own brand new code will use top-notch logging.

    2. Now for the tricky part. Let’s make the example stack I listed above taking configuration from one source (our config files) and writing to one target (files, listed in our configuration)
      1. All the tools using SLF4J will just work. That includes dozen of Apache projects, inc. Camel and Mina, some SpringSource projects and many others.
      2. Now let’s start rolling with all the rest. This is how you do it (click to enlarge):
        Bridging architecture
        1. Jakarta Commons Logging:
          1. Remove commons-logging.jar from your classpath. Usually, it is transitive dependency from the framework, so you need to instruct your build tool on how to do it. What a lucky coincidence, I just wrote short and instructive blog post about how to do it!
          2. Add jcl-over-slf4j.jar instead. It contains alternative commons-logging API implementation, so the code will run just fine.
        2. Log4J:
          1. Same goes here! Remove log4j.jar from your classpath (Again, it would usually be a transitive dependency from the framework, look here).
          2. Add log4j-over-slf4j.jar instead. It contains alternative log4j API implementation, so the code will run just fine.
        3. JUL:
          1. Well, you can’t remove JUL from classpath (it’s a part of the JRE, dude). For the same reason SLF4J can’t reimplement JUL’s API.
          2. Add jul-to-slf4j.jar. It will translate java.util.logging.LogRecord objects into their SLF4J equivalent.
          3. Install SLF4JBridgeHandler and LevelChangePropagator.
          4. Expect 20% decrease in performance (so use it wisely).

All done. Now both our code and all the 3rd paries configured from single source and write to single target. Hooray!

* syslog4j claims it is cross-platform. Well,  I’ll just quote: “Is Syslog4j cross-platform? Yes! Syslog4j UDP/IP and TCP/IP clients should work in any typical Java JRE environment.”

Written by JBaruch

22/06/2011 at 08:40

Posted in Frameworks

Tagged with , , , , ,

Integrating MongoDB with Spring

with one comment

Apparently, most of the visitors to my “Integrating MongoDB with Spring Batch” post can’t find what they look for, because they look for instructions how to integrate MongoDB with plain Spring Core.
Well, the source includes that integration, but it’s on github, and anyway that wasn’t the focus of that post.
So, here’s the integration – short, plain and simple:

  • Properties file with server and database details (resides in classpath in this example):
2    db.port=27017
  1. application-config.xml (or whatever you call it):
    1<beans xmlns=""
    2       xmlns:xsi=""
    3       xmlns:context=""
    4       xsi:schemaLocation="
    7 ">
    8    <context:property-placeholder 
    9                location=""/>
    10    <bean id="mongo" class="com.mongodb.Mongo">
    11       <constructor-arg value="${}"/>
    12       <constructor-arg value="${db.port}"/>
    13   </bean>
    14   <bean id="db" 
    15      class="com.mongodb.spring.config.DbFactoryBean">
    16       <property name="mongo" ref="mongo"/>
    17       <property name="name" value="${}"/>
    18   </bean>
  2. The com.mongodb.spring.config.DbFactoryBean class:
    1 public class DbFactoryBean implements FactoryBean<DB> {
    3        private Mongo mongo;
    4        private String name;
    6        @Override
    7        public DB getObject() throws Exception {
    8            return mongo.getDB(name);
    9        }
    11       @Override
    12       public Class<?> getObjectType() {
    13           return DB.class;
    14       }
    16       @Override
    17       public boolean isSingleton() {
    18           return true;
    19       }
    21       public void setMongo(Mongo mongo) {
    22           this.mongo = mongo;
    23       }
    25       public void setName(String name) {
    26  = name;
    27       }
    28 }
1    @Configuration
2    public class ApplicationConfiguration {
4        @Value("${}")
5        private String appDbName;
7        @Value("${}")
8        private String dbHost;
10       @Value("${db.port}")
11       private int dbPort;
14       @Bean
15       public DB db() throws UnknownHostException {
16           return mongo().getDB(appDbName);
17       }
19       @Bean
20       public Mongo mongo() throws UnknownHostException {
21           return new Mongo(dbHost, dbPort);
22       }
23   }

That’s, actually, it – enjoy. If you feel some part of the puzzle is missing, please leave a comment.

Written by JBaruch

30/05/2010 at 16:25

Posted in Frameworks, Friendly Java Blogs

Tagged with , ,

Integrating MongoDB with Spring Batch

with 4 comments

Update (May 30th 2010):
If you look for plain core Spring integration with MongoDBhere’s a post for you.

Spring Batch is a superb batch framework from, well, Spring. It covers all the concepts of batch architecture and, generally, spares you from reinventing the wheel. It’s cool, really. If you have batch-oriented application, you must go and take a look at Spring Batch. And if you don’t know what batch-oriented application is, just think about reading-validating-saving-to-db a zillion text files every night, unattended. Now you know what batch-oriented application is, go and look at Spring Batch.

Welcome back. As you’ve seen, Spring Batch constantly saves its state in order to be able to recover/restart exactly when it stopped. JobRepository is the bean in charge of saving the state, and its sole implementation uses data access objects layer, which currently has two implementations – in-memory maps and JDBC. It looks like this:

JobRepository class diagram

Of course, the maps are for losers testing,  JDBC implementation is the one to use in your production environment, since you have RDBMS at your application anyway, right? Or not…

Today, when NoSQL is gaining momentum (justified, if you ask me) the assumption that  “you always have RDBMS in enterprise application” is not true anymore. So, how can you work with Spring Batch now? Using in-memory DAOs? Not good enough. Installing, setting up, maintaining, baby-sitting RDBMS only for Spring Batch meta-data? Hum, you’d rather not. There is a great solution – just keep the meta-data in the NoSQL database you use for the application itself. Thanks to Spring, the Spring Batch architecture is modularized and loosely-coupled, and all you have to do in order to make it work is to re-implement the four DAOs.

So, here’s the plan:

  • Implement *Dao with NoSqlDb*Dao
  • Add them to Spring application context
  • Create new SimpleJobRepository, injecting your new NoSqlDb DAOs into it
  • Use it instead of the one you would create from JobRepositoryFactoryBean
  • Profit

That was exactly what I did for our customer, implementing the DAOs using MongoDB. Guess what, you must go and take a look at MongoDB.  It’s lightning-fast, schema-less document-oriented database, that kicks ass. When you suddenly have a strange feeling that RDBMS might not be the best solution for whatever you do, chances are you’d love MongoDB, as I do now. There are use-cases, in which you just can’t implement whatever you need to do with relational storage. Well, I lied. You can. It will take a year, it will look ugly and perform even worse. That’s my case, and I am just happy the year is 2010 and we know by now that one size doesn’t fit all.

I have to admit -implementing Spring Batch DAOs with MongoDB was fun. Even Spring Batch meta-data model, which was designed with relational storage in mind, persists nicely in MongoDB. Should I even mention that the code is cleaner comparing to JDBC? Even on top of JDBC template?

Now go and grab the Spring Batch over MongoDB implementation and the reference configuration: I have used the samples and the tests from original Spring Batch distribution, trying to make as few changes as necessary. You’ll need MongoDB build for your platform and Gradle 0.9p1 to build and run. (Why Gradle? Because it is truly a better way to build).

If you use MongoDB – enjoy the implementation as is. If you use some other document-oriented DB, the conversion should be straightforward. In any case, I’ll be glad to hear your feedback.

Written by JBaruch

27/04/2010 at 15:10


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