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Java Programming Technology

What are Some Essential Java Libraries? 77

rleclerc writes "I would like to ask those 'Javaniers' in the Slashdot community what they thought were essential non-standard libraries that every Java coder should have. Normally I roll my own when it comes to that type of thing and simply build on whats available in the foundation classes. However, recent work has pushed me toward looking at some scientific libraries and I thought I would find out what libraries others in the Java community would consider an essential weapon in their Java arsenal. A few that I am looking at are the Cern scientific libraries and the Apache Commons Collections libraries. To avoid extra libraries I have opted to use the Java logging rather than the Apache one. Anyone like to add anything to the list?"
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What are Some Essential Java Libraries?

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  • For server based applications JMX is a must.
    Don't write off log4j.

    Spring is very good indeed.
  • List (and reasons) (Score:5, Informative)

    by sameb ( 532621 ) on Tuesday December 14, 2004 @07:47PM (#11087726) Homepage
    In no particular order...

    Commons Logging. [] Yeah, you said you wanted to avoid extra libraries, but the overhead of commons logging is so incredibly small, and the extra libraries you'll want to otherwise use are going to require it anyway. It's a measly 28KB last I checked, and well worth it.

    HttpClient [] If you want to do any form of HTTP transfers, avoid HttpUrlConnection (built in to Java) at all costs. The HttpUrlConnection code is broken in many ways (too many to list), so you'll need another library. HttpClient does a good job of hiding the HTTP transfer behind the scenes, and has easy ways of letting you extend/change what you need.

    JGoodies Looks [] Swing is getting better every day, but for that extra polish, you'll want to use the JGoodies Looks library. It does a great job of making Metal look just that much better, and also helps out the Windows L&F in some places.

    Xerces [] I'm not sure if the bulk of this is included in the latter versions of Java, but Xerces is definitely a must-have for any XML parsing.

    Other goodies...

    For rendevous (multicast DNS) support, use jmDNS []. It just works.

    If you need i18n handling (normalization, etc..), IBM's icu4j [] does a great job.

    • I agree but with one change. JDOM is far easier to use than xerces. Also, the swt GUI tools in Eclipse are a nice improvement over swing.

    • by Anonymous Coward
      The HttpUrlConnection code is broken in many ways (too many to list), so you'll need another library.

      How many other classes in the Java standard library are the same way? I'm trying to formulate a position on whether Java would've been better off to not have so many classes by default and rely on some other process to build a big armory of classes (like Perl), or if they indeed took the right path by having so many classes by default (it means companies can build on a huge amount of code that comes di
      • by sameb ( 532621 )
        It's a tough question. Many of the built-in Java classes work wonders, and by building them in, it lets other built-in classes make use of them instead of having to build their own versions. One example is the Collections API. Sure, there could be things added/removed/changed with the API and things like ArrayList, LinkedList, HashMap, TreeSet, etc... but by including them, other necessary stuff can be simpler because they don't have to worry about a simple list or queue.

        The remaining object-oriented pr
    • Castor [] will do generate Java classes from you XML Schema and make XML IO and validation easy. The support for Schema is not 100% (some simple types are missing and not support for keys) but overall it's a great help for avoiding writing boring IO code.
  • by Anonymous Coward
    jython []
  • My top 5 (Score:4, Informative)

    by jacoberrol ( 561252 ) <jacoberrol @ h o t m a> on Tuesday December 14, 2004 @07:50PM (#11087766)
    These are my top 5
    • Logging - log4j (I agree with the previous poster. Don't write log4j off)
    • Unit Test - junit
    • Xml Serialization - xstream (very light-weight and easy to use object->xml serialization )
    • Data access - iBATIS (a beautifully simple data access layer)
    • App framework - Spring (not just for the web controller... the IoC and AOP stuff is quite nice.)
  • JDOM for processing and manipulating XML, real easy to use.
  • My last couple... (Score:4, Insightful)

    by (H)elix1 ( 231155 ) <> on Tuesday December 14, 2004 @07:53PM (#11087818) Homepage Journal
    The last several projects have included jakarta-regexp-1.3.jar. Yes, if you are lucky enough to be able to count on using JDK 1.4 you have another option. One jar and you are golden for regular expressions.

    The other is import org.apache.xpath.XPathAPI; My god is it nice to be able to say

    NodeList nl = XPathAPI.selectNodeList(doc, "config/adapter/config/property[@name='foo']");

    than the normal horking about with SAX or DOM parsers.
    • I've found that the only really working regex library is jregex. All the others just have too many bugs (even the builtin jdk1.4 one). In most of them split can't handle empty fields.

      -the hermit
  • A few I use a lot (Score:3, Informative)

    by eyeball ( 17206 ) on Tuesday December 14, 2004 @08:00PM (#11087895) Journal
    Mozilla's LDAP SDK [] when doing LDAP work

    The pre-1.5 concurrent threading classes []

    Command-line argument handler library []

    Log4J [] logging.
  • by Pengo ( 28814 ) on Tuesday December 14, 2004 @08:04PM (#11087927) Journal

    First, make a plan of what your trying to do.. then go browse apache Commons.

    There have been many times I got through a project, or part way into it.. and realized I could of saved a TON of time by using a tool from that resource.

    If your doing anything with XML, it's worth taking a look at JDom.

    Make sure your using Eclipse, and if your doing web based projects.. I highly recomend I have been a subscribe for a while, and have really enjoyed the enhancements that their modules bring for web development.

  • My top 3 (well 4 actually) would be:
    • commons_lang
    • commons_logging + log4j
    • JUnit

    The rest depends on the frameworks I am using and the project.

    I used to roll my own, but now I tend to do a web search for what I want before resorting to building my own.
  • cglib and more (Score:4, Interesting)

    by Earlybird ( 56426 ) <> on Tuesday December 14, 2004 @09:08PM (#11088569) Homepage
    cglib [], a library that lets you do metaclass programming efficiently in Java; it's similar to java.lang.reflect.Proxy, but more flexible and compiled to bytecode. Cglib is commonly used to create decorators -- for example, Hibernate uses it to generate proxies, to transparently track whether persistent objects have changed in memory and must be re-saved to the database -- but there are other uses, such as mimicking the mixin pattern.

    Xalan [] for XSLT and XPath processing. Here's a tip: Never, ever use SAX for XML parsing of application-specific data structures. SAX is a nice low-level interface for building upon, but unless you're programmatically emitting a document from scratch, it's painful to use -- you always end up writing a stack-based content handler to keep nesting state. XPath makes parsing a breeze.

    JGroups [] (formerly JavaGroups) is a protocol stack for building reliable, fairly efficient network communications based on, among other things, multicast IP. The entire stack is user-defineable, so you can pick and choose the level of reliability and which features you want (TCP support, pinging, group membership management etc.).

    Lucene [] is a text-indexing engine. It's actually pretty crap, and does not scale very far (we're talking a few seconds for result sets of only a few thousand documents), and the code is pure spaghetti (abstract base classes! Inheritance!), but if you need a little indexing engine or some decent text tokenization classes, and your performance requirements are modest, it works well enough.

    SableCC [] is a good BNF-based parser generator that generates type-safe parse trees that can navigated at runtime. Unlike the more well-known JavaCC [], it's easy to get started, not least because the BNF-like grammar is so simple.

    • Re:cglib and more (Score:3, Informative)

      What's wrong with abstract base classes and inheritance? These are fundamental concepts of OO. Spaghetti code can be written in any language, regardless of these features.
        • What's wrong with abstract base classes and inheritance?

        Nothing -- if you use them correctly. In the case of Lucene, there is no clear separation between interface and implementation, and the implementation itself frequently violates good design principles such as separation of concerns and encapsulation. (The author of Lucene also seems ignorant of the fact that Java has an interface keyword. Pure abstract base classes have their place in MI languages like C++, of course.)

      • What's wrong with abstract base classes and inheritance? These are fundamental concepts of OO. Spaghetti code can be written in any language, regardless of these features.

        Because inheritance breaks encasulation. When given the choice between composition and inheritance, you should always choose composition. With a well encasulated library, you won't need to dig into the source. Chances are, with a lot of inheritance, you'll need the original library source even for the most basic use of that library.
    • COLT:
  • "Patterns in Java" in 2 volumes from JWiley...this is midway between the library and DIY. The library may not exactly meet your need and you will spend some time reading code and hacking or building a layer on top of the library. And DIY, as you know, is always started as a Quick and Dirty project that quickly proves less Q and more D than is the most work. And a pattern, assuming you find one that fits your needs, brings experience or understanding of the problem to your project that a librar
  • Usefull libraries (Score:3, Informative)

    by Anonymous Coward on Tuesday December 14, 2004 @10:08PM (#11089040)
    We've found that the below libraries usually suit most applications:
    • log4j - Killer logging tool
    • ant - Killer build tool
    • junit - Killer unit test tool
    • xerces - XML parser
  • One of the easiest ways I've seen to do text IO and processing is to just write some stubbies in Jython - to open a file, write to it, etc. Regex stuff can be simplified this way too. Basically, just a wrapper class.

    Caveat: I haven't used Java since about 1.3, and I hear they've improved the text APIs significantly in 1.4 (or was it 1.5?).
  • Yajul (Score:3, Informative)

    by utahjazz ( 177190 ) on Tuesday December 14, 2004 @11:25PM (#11089553)
    Yajul [] has all the the little things you normally have to write and test yourself.

    It has lots of obvious classes that you'd almost expect in the JDK like TeeOutputStream, ByteCountingOutputStream, Cache, and StringUtil.
  • My Favorites (Score:5, Informative)

    by 2starr ( 202647 ) on Tuesday December 14, 2004 @11:32PM (#11089606) Homepage
    GlazedLists [] - UI List/Table Manipulation

    Doug Lea's Concurrency Utilities [] - If you haven't yet made the plunge to Java 5.0, this is indispensable for anything thread related.

    Trove4J [] - High performance collections that work with primitives. We do wire-speed packet capture and flow analysis with this stuff. 'nuf said.

  • My most favourite (Score:4, Interesting)

    by Lao-Tzu ( 12740 ) on Tuesday December 14, 2004 @11:49PM (#11089682) Homepage

    I'm currently building a variety of petroleum engineering tools in Java. Here are the libraries I've found most useful:

    JFreeChart [] - for all your plotting needs. Robust, quick, and fairly bug free. Not perfect, but hackable.

    iText [] - a free Java PDF library. My preferred method for creating reports, especially since a lot of my output needs to be e-mailed or submitted to the government, not printed out.

    JAMA [] - a Java Matrix package. The fact that this library has a working singular value decomposition has saved me bunches of time programming a boring and tricky algorithm. I guess it has other stuff, too.

  • Most of the big ones have already been touched on.

    A couple of template packages that are good:
    Freemarker []
    Velocity [].

    And if you need to perform pdf manipulation: Big Faceless Java PDF Library [] It's not free but it's a really nice package

    • Don't use Velocity. It is a nice, simple template language, but you suddenly bang your head against its limitations. Mainly, it's only got macros, not composable procedures, which makes life a pain in the arse.

      I haven't used FreeMarker, but it claims to fix that kind of stuff. Next time...

    • Another templating package is Jelly [] the avantage is that it uses a syntax that's quite similar to JSLT.
    • Interesting, this is the first post I could find that mentions any framework libraries. Does everyone here just use straight JSP?

      I would be interested in /.er's opinions on framework libraries such as struts [] and hibernate [].

  • by Anonymous Coward
    DynaBean, RowSetDynaClass and ResultSetDynaClass are IMHO better than any other DAO. They work like java beans. but unlike statically defined java beans they can have arbitrary number of fields. DynaBean is a dynamic-DAO without code gen. the fields are defined according to ResultSetMetadata. if your resultset has 10 columns the bean has 10 fields. if your resultset is from a 10+15 table join you have 25 fields in the bean. you can turn the beans into an xml representation. it lacks compile type field name
  • is ofcourse the ultimate library you need, it should be part of Java.

    Apache offers a lot of good tools, most of which are considered "standard". Jakarta Commons and Xerces in particular.

    If you need to create custom parsers (i.e. embedded languages or custom file format), take a look at

    Other than those, I use no external libraries at the moment, mainly because I have no need for anything else.
  • ... recently I discovered TableLayout. Most Swing guis I code nowadays use it. Very flexible and much easier to use than GridBagLayout. []
  • It really depends on what you want to do. But generally my starting points usually are for db related stuff hibernate for many other things stuff from the jakarta project (much of the commons stuff, xerces, log4j and others) and from there usually it becomes rougher, swing you cannot do wrong with the jgoodies stuff from, Karsten Lentzsch has done an excellent work) otherwise it depends on the task and license.
  • by LadyLucky ( 546115 ) on Wednesday December 15, 2004 @04:32AM (#11090722) Homepage
    If it comes from apache, use it. There's so much!
    • Log4j (really, reconsider using it, it's the industry standard even with the 1.4 logging stuff, that should tell you something)
    • Tomcat for servlets, it's great
    • Velocity for a templating engine
    • Commons for your utility junk
    • Ant for building stuff
    I would also recomment as another poster has Doug Lea's concurrency utilities. If you have *anywhere* written an Object.wait() or a Object.notify[all](), then replace it with these libraries.

    Junit is indespensible and these days with the IDEs indistinguishable from the core java libraries themselves.

    Don't write SQL, use hibernate.

    For security, you cant go past the legion of the bouncy castle (I'm serious)

    Use cruise control to set up a continuous build

    And the *only* piece of closed source code we rely on is Clover coverage. It's simply fantastic. You'll love it if you adopt unit testing as your quality mechanism.

    • I agree whole heartedly on everything you say. (Except maybe absolutly saying to use hibernate instead of SQL... I've run into sld situation where I wouldn't recommend it.)

      Anyhow... I'm going to be starting a job soon where Maven is the build tool instead of ANT. I've been using ANT for years. Does /. have any wisdom on Maven? As I understand it, it seems to be an "enterprise" version of ant, where the projects are fractured and co-dependant.

      Does anyone know of any good references... I wasn't able to
      • Honestly, I think maven is atrocious.

        The Bile Blog [] has plenty to say about it.

        I think Maven may work if you don't mind drinking a bit of kool aid and structuring your project around your build tool, rather than the other way round.

  • If you want to do text templating, but are turned off by JSP, you might want to take a look at Jamon []. Jamon templates can received typed parameters, support template inheritance, and a wealth of other features. It's very much inspired from perl's Mason.
  • Fastutil (Score:2, Interesting)

    by BoxedFlame ( 231097 )
    fastutil [] is what Jakarta Commons Collection should've been: an actually competent implementation of truly type safe containers.

    MG4J [] from the same place is pretty interesting too.
  • Don't forget xmlenc [], an XML output library.

    It's simple, fast and the memory footprint is negligible. It does not have the overhead of DOM-based solutions.
  • jdbc, snmp, (Score:2, Informative)

    by speculatrix ( 678524 )
    stating the obvious, no server-side java is complete without a DB!

    JDBC - mysql or postgresql or oracle-classes.jar

    we, an ISP, do lots of networky stuff with SNMP; Jonathan Sevy has a nice easy to use class library: evy/snmp/s nmp_package.html

  • Many of my favorites have already been mentioned: junit, jdom, xstream, log4j, and many things from Jakarta Commons.

    The other things I use regularly are HttpUnit [], a virtual web client and Prevayler [], a simple Java persistence framework.
  • [] Is a great package if you need to do any kind of map display.
  • XOM! (Score:3, Informative)

    by CraigoFL ( 201165 ) <> on Wednesday December 15, 2004 @10:25AM (#11091866)
    XOM [] is an excellent XML-handling library. It makes XML parsing, interpretation, and generation a breeze, and goes to great lengths to ensure that what you do is correct according to the XML specs. It's an absolute pleasure to use, especially compared to the "standard" SAX and DOM libraries.

    It's created by Elliotte Rusty Harold, who is one of the bigwigs in both the XML [] and Java [] arenas. XOM is at the intersection of those two sets.

    Technically it's still in "beta", but the API hasn't changed at all since the Alpha releases, and all the bugs fixed in the beta stages have been for performance boosts or to fix bugs dealing with the very fringes of XML.

    Probably the best part of the library isn't the code itself; it's the design process that went into making it. Check out the Design Principles [] for a good read.


  • If you whip up domain-specific languages (DSLs) often, ANTLR is an excellent tool for writing lexers and parsers and tree parsers.

    (Tree parsers parse the syntax tree generated by the parser (optional) for doing multi-pass semantic / compile checks, for example.)

    Once you've learned the techniques for DSLs you start to use them everywhere, especially in large architectural design).
  • by 4of12 ( 97621 )

    Might look around at NIST [].

    A few years ago I saw a nice presentation from one of the NIST people about getting the best Java performance for scientific computational tasks.

  • Provides a nice OO wrapper around a SAX based XML parser. []

  • Some usefull stuff that I actually *use* besides all the great tools mentioned above (in no particular order):

Whenever people agree with me, I always think I must be wrong. - Oscar Wilde