Python, EiffelQC#QRoby{无一例外地都使用?jin)GC机制。但既然Java中的GC最名，所以天?br /> 下来自然应该抗着?/span>
q篇短文源于comp.lang.java.programmer跟comp.lang.c++上发生的一场大辩论Q支持C++和Java
的两z不同势力展开?jin)新世纪W一场冲H，跟脓(chung)发言过350Q两zN有名角压c(din)C++阵营的擂L
Pete BeckerQACM?x)员QDinkumware Ltd. 的技术副ȝ。此君精通C++和JavaQ开发过两种语言?br />
核心(j)cdQ但是却对C++狂热之极Q而对于Java颇不以ؓ(f)然。^时谈到Java的时候还好，一旦有
敢用Java来批判C++Q立d不住火爆脾气跛_出来Q以坚韧不拔的毅力和大无畏精与Ҏ(gu)周旋Q?br />
舌战儒Q哪怕只剩下一个h也要血战到底。这{奇人当真少见！我真奇怪他整天泡在usenet上，
不用工作么？他的老板P.J. Plauger如此宽宏大量QJava阵营主角是一个网名Razzi的兄弟，另外?br />
Sun公司大名鼎鼎的Peter van der Linden助阵Q妙语连珠，寸土必争Q加上h多势众，一度占据优ѝ?br />
C++阵营里大拿虽然很多，但是大多数没有Pete那么多闲工夫Q例如Greg ComeauQComeau公司老板Q?br />
每次来个只言片语Q实在帮不了(jin)Pete多大忙。但是自从C++阵营中冒Z个无名小子，|名Courage(勇气)Q?br />
发动对Java GC机制的批判，形势Z一变。C++阵营g处于全攻之势QJava阵营疲于防守Q只?br />
招架_(d)(x)“你们没有证据Q没有统计资?#8221;QŞ势很被动?/span>
垃圾攉(GC)不是一直被Java fans用来炫耀Q引以ؓ(f)傲的优点么？怎么成了(jin)q?jin)？我大惑不解，定?br /> 一看，才觉得此中颇有道理?/span>
首先QJava Swing库存在大量资源泄漏问题，q一点SUN非常清楚Q称之ؓ(f)bugsQ正在极力修正。但是看?br />
q里的问题恐怕不仅是库编写者的疏忽Q可能根源在于深层的机制Q未必能够轻易解冻I搞不好要伤筋动骨?br />
不过q个问题?sh)是那么?gu)QC++阵营觉得如果抓住Ҏ(gu)的弱Ҏ(gu)击，q是占?jin)上风也没什么说服力。谁
没有~点呢？于是反其道而行之，猛烈dJava阵营觉得最得意的东西，Java的GC机制本n?/span>
首先来想一惻Imemory leak到底意味着什么。在C++中，new出来的对象没有deleteQ这导致了(jin)memory
leak。但是C++早就有了(jin)克服q一问题的办法——smart pointer。通过使用标准库里设计_致的auto_ptr
以及(qing)各种STL容器Q还有例如boost?差不多是个准标准库了(jin))中的四个smart pointersQC++E序员只?br />
׃一个星期的旉学习(fn)最新的资料Q就可以拍着胸脯_(d)(x)“我写?/span>E序没有memory leak!”?/span>
相比之下QJavag更优UQ因Z一开始你׃用考虑什么特D的机制Q大胆地往前newQ自有GC替你
收拾D局。Java的GC实际上是JVM中的一个独立线E，采用不同的算?/span>{略来收集heap中那些不再有
reference指向的垃圑֯象所占用的内存。但是，通常情况下，GCU程的优先比较低，只有在当?/span>E序
I闲的时候才?x)被调度Q收集垃圾。当?dng)如果JVM感到内存紧张?jin)，JVM?x)主?/span>调用GC来收集垃圾，获取
更多的内存。请注意QJava的GC工作的时机是Q?. 当前E序不忙Q有I闲旉?. I闲内存?sh)?br />
现在我们考虑一U常见的情况Q?/span>E序在紧张运行之中，没哟I闲旉lGC来运行，同时机器内存很大Q?br />
JVM也没有感到内存(sh)Il果是什么？对了(jin)QGC形同虚设Q得不到调用。于是，内存被不断吞噬，而那?br />
早已l用不着的垃圑֯象仍在在宝贵的内存里睡大觉。例如：(x)
class BadGc {
public void job1() {
String garbage = "I am a garbage, and just sleeping in your precious memory, " +
"how do you think you can deal with me? Daydreaming! HAHA!!!";
....
}
public void job2() {...}
...
...
public void job1000() {...}
public static void main(String[] args) {
bgc = new BadGc();
bgc.job1();
bgc.job2();
...
bgc.job1000();
}
}
q行中，虽然garbage对象在离开job1()之后Q就再也没有用了(jin)。但是因?/span>E序忙，内存q够用，所以GC?br /> 不到调度Qgarbage始终不会(x)被回Ӟ直到E序q行到bgc.job1000()时还w在内存里嘲W你。没辙吧Q?/span>
好了(jin)Q我承认q段E序很傻。但是你不要以ؓ(f)q只是理Z的假设，恰恰相反Q大多数实用中的JavaE序都有
cM的效应。这是Z么JavaE序狂耗内存，而且好像l它多少内存吃都不够。你׃大笔的银子把内存
?28升到256Q再升到512Q结果是Q一旦执行复杂Q务，内存q是被轻易填满，而且多出来的q些内存只是
用来装垃圾，GCq是不给面子地千g唤不出来。等C的内存终于心(j)力交瘁，GC才姗姗来q，收拾D局。?br />
且GC工作的方式也很不好评P一U方法是一旦有Z(x)回收内存Q就把所有的垃圾都回收。你可以惌Q这?br />
花很长时?几百M的垃圑֕Q?Q如果你q时侯正在压下开炮的按钮QGC却叫?jin)暂定，好?jin)Q你{死吧！另一
U方法，得到Z(x)之后Q回收一些内存，让JVM感到内存?sh)那么紧张时收手。结果呢Q内存里始终有大批垃
圾，E序始终在半Mzȝ荡着。最后，GC可以每隔一D|间就q行一ơ，每次只回收一部分垃圾Q这是现?br />
大部分JVM的方式，l果是内存(sh)费?jin)，q动不动暂停几百毫秒。难啊！
反过来看看C++利用smart pointer达成的效果，一旦某对象不再被引用，pȝM容缓Q立d收内存。这
通常发生在关键Q务完成后的清?cleanup)时期Q不?x)?jing)响关键Q务的实时性，同时Q内存里所有的对象
都是有用的，l对没有垃圾I占内存。怎么P传统、朴素的C++是不是更胜一{？
据统计，目前的JavaE序q行期间占用的内存通常为对应C++E序?-20倍。除?jin)其它的原因Q上面所说的是一?br /> 非常主要的因素。我们对memory leak如此愤恨Q不是因ؓ(f)它导致大量的内存垃圾得不到清除吗Q如果有?br /> GC之后Q垃圾比以前q来势v汹，那么GC又有什么好处呢Q?/span>
当然QC++的smart pointer现在?x)用的Z多，所以现在的C++E序普遍存在更严重的memory leak问题?br /> 但是Q如果我奶奶跟舒马赫比赛车输掉了(jin)Q你能够埋怨那辆R子么Q?br /> http://www.594k.com/java/html/y2007m1/12051/
]]>
一、LiveJournal发展历程
LiveJournal?9q始于校园中的项目，几个人出于爱好做?jin)这样一个应用，以实C下功能：(x)
- 博客Q论?
- C会(x)性网l，扑ֈ朋友
- 聚合Q把朋友的文章聚合在一?
LiveJournal采用?jin)大量的开源YӞ甚至它本w也是一个开源Y件?
在上U后QLiveJournal实现?jin)非常快速的增长Q?/p>
- 2004q?月䆾Q?80万注册用戗?
- 2005q?月䆾Q?80万注册用戗?
- 2005q?月䆾Q?90万注册用戗?
- 辑ֈ?jin)每U钟上千ơ的面h?qing)处理?
- 使用?jin)大量MySQL服务器?
- 使用?jin)大量通用lg?
二、LiveJournal架构现状概况
三、从LiveJournal发展中学?/h2>
LiveJournal?台服务器发展?00台服务器Q这其中l历?jin)无数的伤痛Q但同时也摸索出?jin)解册些问题的?gu)Q通过对LiveJournal的学?fn)，可以让我们避免LJ曄犯过的错误，q且从一开始就对系l进行良好的设计Q以避免后期的痛苦?/p>
下面我们一步一步看LJ发展的脚步?/p>
1、一台服务器
一 台别人捐助的服务器，LJ最初就跑在上面Q就像Google开始时候用的破服务器一P值得我们敬。这个阶D，LJ的h以惊人的速度熟?zhn)的Unix的操 作管理，服务器性能出现q问题，不过q好Q可以通过一些小修小改应付过厅R在q个阶段里LJ把CGI升C(jin)FastCGI?/p>
最l问题出C(jin)Q网站越来越慢，已经无法通过优过化来解决的地步，需要更多的服务器，q时LJ开始提供付Ҏ(gu)务，可能是想通过q些钱来购买新的服务器，以解军_时的困境?br /> 毫无疑问Q当时LJ存在巨大的单炚w题，所有的东西都在那台服务器的铁皮盒子里装着?/p>
2、两台服务器
用付Ҏ(gu)务赚来的钱LJC(jin)两台服务器：(x)一台叫做Kenny的Dell 6U机器用于提供Web服务Q一台叫做Cartman的Dell 6U服务器用于提供数据库服务?/p>
LJ有了(jin)更大的磁盘，更多的计资源。但同时|络l构q是非常单，每台机器两块|卡QCartman通过内网为Kenny提供MySQL数据库服务?br />
暂时解决?jin)负载的问题Q新的问题又出现?jin)?x)
- 原来的一个单点变成了(jin)两个单点?
- 没有冷备份或热备份?
- |站速度慢的问题又开始出C(jin)Q没办法Q增长太快了(jin)?
- Web服务器上CPU辑ֈ上限Q需要更多的Web服务器?
3、四台服务器
又买?jin)两収ͼKyle和StanQ这ơ都?U的，都用于提供Web服务。目前LJ一共有3台Web服务器和一台数据库服务器。这旉要在3台Web服务器上q行负蝲均横?/p>
LJ把Kenny用于外部的网养I使用mod_backhandq行负蝲均横?/p>
然后问题又出C(jin)Q?/p>
- 单点故障。数据库和用于做|关的Web服务器都是单点，一旦Q何一台机器出现问题将D所有服务不可用。虽然用于做|关的Web服务器可以通过保持?j)蟩同步q速切换，但还是无法解x(chng)据库的单点，LJ当时也没做这个?
- |站又变慢了(jin)Q这ơ是因ؓ(f)IO和数据库的问题，问题是怎么往应用里面d数据库呢Q?
4、五台服务器
又买?jin)一台数据库服务器。在两台数据库服务器上用了(jin)数据库同?Mysql支持的Master-Slave模式)Q写操作全部针对L据库Q通过BinlogQ主服务器上的写操作可以q速同步到从服务器上）(j)Q读操作在两个数据库上同时进?也算是负载均横的一U吧)?/p>
实现同步时要注意几个事项Q?/p>
- L作数据库选择法处理Q要选一个当前负载轻一点的数据库?
- 在从数据库服务器上只能进行读操作
- 准备好应对同步过E中的gq，处理不好可能?x)导致数据库同步的中断。只需要对写操作进行判断即可，L作不存在同步问题?
5、更多服务器
有钱?jin)，当然要多C服务器。部|后快了(jin)没多久，又开始慢?jin)。这ơ有更多的Web服务器，更多的数据库服务器，存在 IO与CPU争用。于是采用了(jin)BIG-IP作ؓ(f)负蝲均衡解决Ҏ(gu)?/p>
6、现在我们在哪里Q?/h2>
现在服务器基本上够了(jin)Q但性能q是有问题，原因出在架构上?/p>
数据库的架构是最大的问题。由于增加的数据库都是以Slave模式d到应用内Q这样唯一的好处就是将L作分布到?jin)多台机器，但这样带来的后果是写操作被大量分发Q每台机器都要执行，服务器越多，费p大，随着写操作的增加Q用于服务读操作的资源越来越?/p>
׃台分布到两台
最l效?/p>
现在我们发现Q我们ƈ不需要把q些数据在如此多的服务器上都保留一份。服务器上已l做?jin)RAIDQ数据库也进行了(jin)备䆾Q这么多的备份完全是对资源的费Q属于冗余极端过度。那Z么不把数据分布存储呢Q?/p>
问题发现?jin)，开始考虑如何解决。现在要做的是把不同用L(fng)数据分布C同的服务器上q行存储Q以实现数据的分布式存储Q让每台机器只ؓ(f)相对固定的用h务，以实现^行的架构和良好的可扩展性?/p>
??jin)实现用户分l，我们需要ؓ(f)每一个用户分配一个组标记Q用于标记此用户的数据存攑֜哪一l数据库服务器中。每l数据库׃个master?qing)几个slave l成Qƈ且slave的数量在2-3収ͼ以实现系l资源的最合理分配Q既保证数据L作分布，又避免数据过度冗余以?qing)同步操作对pȝ资源的过度消耗?/p>
׃収ͼ一l）(j)中心(j)服务器提供用户分l控制。所有用L(fng)分组信息都存储在q台机器上，所有针对用L(fng)操作需要先查询q台机器得到用户的组P然后再到相应的数据库l中获取数据?/p>
q样的用h构与目前LJ的架构已l很相像?jin)?/p>
在具体的实现旉要注意几个问题：(x)
- 在数据库l内不要使用自增IDQ以便于以后在数据库l之间迁UȝP以实现更合理的I/OQ磁盘空间及(qing)负蝲分布?
- useridQpostid存储在全局服务器上Q可以用自增，数据库组中的相应值必M全局服务器上的gؓ(f)准。全局服务器上使用事务型数据库InnoDB?
- 在数据库l之间迁Uȝh要万分小?j)，当迁UL用户不能有写操作?
7、现在我们在哪里
问题Q?/p>
- 一个全局L务器Q挂掉的话所有用h册及(qing)写操作就挂掉?
- 每个数据库组一个主服务器，挂掉的话q组用户的写操作挂掉?
- 数据库组从服务器挂掉的话?x)导致其它服务器负蝲q大?
对于Master-Slave模式的单炚w题，LJ采取?jin)Master-Master模式来解冟뀂所谓Master-Master实际上是人工实现的，q不是由MySQL直接提供的，实际上也是两台机器同时是MasterQ也同时是SlaveQ互相同步?/p>
Master-Master实现旉要注意：(x)
- 一个Master出错后恢复同步，最好由服务器自动完成?
- 数字分配Q由于同时在两台机器上写Q有些ID可能?x)冲H?
解决Ҏ(gu)Q?br />
- 奇偶数分配IDQ一台机器上写奇敎ͼ一台机器上写偶?
- 通过全局服务器进行分?LJ采用的做??
Master-Master模式q有一U用法，q种Ҏ(gu)与前一U相比，仍然保持两台机器的同步，但只有一台机器提供服务（d写）(j)Q在每天晚上的时候进行轮换，或者出现问题的时候进行切换?/p>
8、现在我们在哪里
现在插播一条广告，MyISAM VS InnoDB?/p>
使用InnoDBQ?/p>
- 支持事务
- 需要做更多的配|，不过值得Q可以更安全的存储数据，以及(qing)得到更快的速度?
使用MyISAMQ?/p>
- 记录日志QLJ用它来记|络讉K日志Q?
- 存储只读?rn)态数据，_快?
- q发性很差，无法同时d数据Q添加数据可以）(j)
- MySQL非正常关闭或L时会(x)D索引错误Q需要用myisamchk修复Q而且当访问量大时出现非常频繁?
9、缓?/h2>
d我写q?a >一文章介lmemcachedQ它?yu)是由LJ的团队开发的一Ƅ存工P以key-value的方式将数据存储到分布的内存?sh)。LJ~存的数据：(x)
- 12台独立服务器Q不是捐赠的Q?
- 28个实?
- 30GBd?
- 90-93%的命中率Q用qsquid的h可能知道Qsquid内存加磁盘的命中率大概在70-80%Q?
如何建立~存{略Q?/p>
想缓存所有的东西Q那是不可能的，我们只需要缓存已l或者可能导致系l瓶颈的地方Q最大程度的提交pȝq行效率。通过对MySQL的日志的分析我们可以扑ֈ~存的对象?/p>
~存的缺点？
- 没有完美的事物，~存?sh)有~点Q?
- 增大开发量Q需要针对缓存处理编写特D的代码?
- 理隑ֺ增加Q需要更多h参与pȝl护?
- 当然大内存(sh)需要钱?
10、Web讉K负蝲均衡
在数据包U别使用BIG-IPQ但BIG-IPq不知道我们内部的处理机Ӟ无法判断由哪台服务器对这些请求进行处理。反向代理ƈ不能很好的vC用，不是已经够快?jin)，是达不到我们想要的效果?/p>
所以，LJ又开发了(jin)Perlbal。特点：(x)
- 快，，可管理的http web 服务?代理
- 可以在内部进行{?
- 使用Perl开?
- 单线E，异步Q基于事Ӟ使用epoll , kqueue
- 支持Console理与httpq程理Q支持动态配|加?
- 多种模式Qweb服务器，反向代理Q插?
- 支持插gQGIF/PNG互换Q?
11、MogileFS
LJ使用开源的MogileFS作ؓ(f)分布式文件存储系l。MogileFS使用非常单，它的主要设计思想是：(x)
- 文g属于c（cL最的复制单位Q?
- 跟踪文g存储位置
- 在不同主Z存储
- 使用MySQL集群l一存储分布信息
- 大容易廉L(fng)?
到目前ؓ(f)止就q么多了(jin)Q更多文可以在http://www.danga.com/words/扑ֈ?a >Danga.com?a >LiveJournal.com?同学们拿q个文参加?jin)两ơMySQL ConQ两ơOS ConQ以?qing)众多的其它会(x)议Q无U的把他们的l验分n出来Q值得我们学习(fn)。在web2.0时代快速开发得到大家越来越多的重视Q但良好的设计仍是每一个应 用的基础Q希望web2.0们在成长为Top500|站的\上，不要因ؓ(f)架构ȝ?jin)网站的发展?/p> http://blog.csdn.net/xmr_gxcfe/archive/2007/09/14/1785292.aspx
]]>
J2EE开发中大量的专业羃略语很是让hqhQ尤其是跟一些高手讨论问题的时候，三分钟就被h家满口的专业术语h?jin)，PO VO BO DTO POJO DAOQ一大堆的就来了(jin)Q听q老罗对这U现象的批判的朋友会(x)?x)?j)一W）(j)?/p>
首先声明偶也不是什么高手，以下ȝ都是自己的体?x)。不对之处请(zhn)多指教?/p>
POQ?br>persistant object持久对象
最形象的理解就是一个PO是数据库中的一条记录?br>好处是可以把一条记录作Z个对象处理，可以方便的{为其它对象?br>
BOQ?br>business object业务对象
主要作用是把业务逻辑装Z个对象。这个对象可以包括一个或多个其它的对象?br>比如一个简历，有教育经历、工作经历、社?x)关pȝ{?br>我们可以把教育经历对应一个POQ工作经历对应一个POQ社?x)关pd应一个PO?br>建立一个对应简历的BO对象处理历，每个BO包含q些PO?br>q样处理业务逻辑Ӟ我们可以针对BOd理?br>
VO Q?br>value object值对?br>ViewObject表现层对?br>
主要对应界面昄的数据对象。对于一个WEB面Q或者SWT、SWING的一个界面，用一个VO对象对应整个界面的倹{?br>
DTO Q?br>Data Transfer Object数据传输对象
主要用于q程调用{需要大量传输对象的地方?br>比如我们一张表?00个字D，那么对应的PO有100个属性?br>但是我们界面上只要显C?0个字D，
客户端用WEB service来获取数据，没有必要把整个PO对象传递到客户端，
q时我们可以用只有q?0个属性的DTO来传递结果到客户端，q样也不?x)暴露服务端表结?到达客户端以后，如果用这个对象来对应界面昄Q那此时它的w䆾p{为VO
POJO Q?br>plain ordinary java object 单java对象
个h感觉POJO是最常见最多变的对象，是一个中间对象，也是我们最常打交道的对象?br>
一个POJO持久化以后就是PO
直接用它传递、传递过E中是DTO
直接用来对应表示层就是VO
DAOQ?br>data access object数据讉K对象
q个大家最熟?zhn)Q和上面几个O区别最大，基本没有互相转化的可能性和必要.
主要用来装Ҏ(gu)据库的访问。通过它可以把POJO持久化ؓ(f)POQ用POl装出来VO、DTO
ȝ下我认ؓ(f)一个对象究竟是什么O要看具体环境Q在不同的层、不同的应用场合Q对象的w䆾也不一P而且对象w䆾的{化也是很自然的。就像你对老婆来说是老公Q对父母来说是子女。设计这些概늚初衷不是Z(jin)唬h而是Z(jin)更好的理解和处理各种逻辑Q让大家能更好的ȝ面向对象的方式处理问?
大家千万不要陷入q度设计Q大可不必ؓ(f)?jin)设计而设计一定要在代码中区分各个对象。一句话技术是为应用服务的?br>
Ƣ迎指正?br>
M(jin)个图Q感觉没有完全表辑և自己的意思。。。。。谁帮忙完善下，最好能体现各个O在MVC中的位置
转自Q?a href="http://www.tkk7.com/vip01/archive/2007/01/08/92430.html">http://www.tkk7.com/vip01/archive/2007/01/08/92430.html
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l. (tng)q接到数据库的方?br />{：(x)1) (tng)ODBC(Open (tng)Database (tng)Connectivity)
(tng) (tng) (tng) (tng) (tng) (tng) (tng)一个以C语言为基讉KSQL为基数据库引擎的接口Q它提供?jin)一致的接口用于和数据库沟通以?qing)访问数据?br /> (tng) (tng) (tng) (tng)2) (tng)JDBC
(tng) (tng) (tng) (tng) (tng) (tng) (tng)Java版本的ODBC
2. (tng)JDBC应用~程接口
{：(x)JDBC应用~程接口是：(x)
(tng) (tng) (tng) (tng)1) (tng)标准的数据访问接口，可以q到不同的数据库;
(tng) (tng) (tng) (tng)2) (tng)JAVA~程语言的一l类和接口?br /> (tng) (tng) (tng) (tng)JDBC应用~程接口能够Q?br /> (tng) (tng) (tng) (tng)1) (tng)q接到数据库;
(tng) (tng) (tng) (tng)2) (tng)发SQL查询字符串到数据?
(tng) (tng) (tng) (tng)3) (tng)处理l果?br /> (tng) (tng) (tng) (tng)JDBC应用~程接口有二个主要的部分Q?br /> (tng) (tng) (tng) (tng)1) (tng)JAVA应用E序开发接口面向JAVA应用E序开发?
(tng) (tng) (tng) (tng)2) (tng)JDBC驱动E序开发接?br /> (tng) (tng) (tng) (tng)
3. (tng)JDBC (tng)Driver
{：(x)1) (tng)一大堆实现?jin)JDBCcd接口的类;
(tng) (tng) (tng) (tng)2) (tng)提供?jin)一个实现java.sql.Driver接口的类?br />
4. (tng)JDBC (tng)Driver的四U类?br />{：(x)1) (tng)JDBC-ODBC?br /> (tng) (tng) (tng) (tng)由O(jin)DBC驱动提供JDBC讉K
(tng) (tng) (tng) (tng)2) (tng)本地API
(tng) (tng) (tng) (tng)部分Java (tng)driver把JDBC调用转化成本地的客户端API
(tng) (tng) (tng) (tng)3) (tng)JDBC-net
(tng) (tng) (tng) (tng)U的Java (tng)driverQ将JDBC调用转入DBMSQ与|络协议无关。然后通过服务器将调用转ؓ(f)DBMS协议?br /> (tng) (tng) (tng) (tng)4) (tng)本地协议
(tng) (tng) (tng) (tng)U的java (tng)driverQ将JDBC调用直接转ؓ(f)DBMS使用的网l协?br />
5. (tng)JDBC开发者接?br />{：(x)1) (tng)java.sql--java (tng)2q_下JDBC的主要功能，标准?J2SE)
(tng) (tng) (tng) (tng)2) (tng)javax.sql--java (tng)2q_下JDBC增强功能Q企业版(J2EE)
6. (tng)使用URL认数据?br />{：(x)我们使用URL来确定一个数据库(正确的Driver,正确的主?正确的协议，正确的协议，正确的用户名和密?;
(tng) (tng) (tng) (tng)语法Qprotocol:subprotocol:subname
(tng) (tng) (tng) (tng)范例Qjdbc:db2:MyTest
(tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng)jdbc:db2://localhost:6789/MyTest
7. (tng)javax.sql包JDBC2.0的增强功?br />{：(x)1) (tng)数据源接?
(tng) (tng) (tng) (tng)2) (tng)q接?
(tng) (tng) (tng) (tng)3) (tng)分布式交?
(tng) (tng) (tng) (tng)4) (tng)行集;
8. (tng)创徏一个基本的JDBC应用
{：(x)1) (tng)步骤一Q注册一个driver;
(tng) (tng) (tng) (tng)2) (tng)步骤二：(x)建立一个到数据库的q接;
(tng) (tng) (tng) (tng)3) (tng)步骤三：(x)创徏一个statement;
(tng) (tng) (tng) (tng)4) (tng)步骤四：(x)执行SQL语句;
(tng) (tng) (tng) (tng)5) (tng)步骤五：(x)处理l果;
(tng) (tng) (tng) (tng)6) (tng)步骤六：(x)关闭JDBC对象
9. (tng)注册一个Driver(步骤一)
{：(x)1) (tng)driver被用于连接到数据?
(tng) (tng) (tng) (tng)2) (tng)JDBC应用~程接口使用W一个能成功q接到给定URL的driver;
(tng) (tng) (tng) (tng)3) (tng)在同一旉可以装蝲多个driver
10.注册一个driver的方法：(x)
{：(x)1) (tng)使用cloader(装蝲;实例?注册入DriverManager)
(tng) (tng) (tng) (tng) (tng) (tng) (tng)a. (tng)Class.forName("Com.ibm.db2.jdbc.app.DB2Driver");
(tng) (tng) (tng) (tng) (tng) (tng) (tng)b. (tng)Class.forName("Com.ibm.db2.jdbc.net.DB2Driver");
(tng) (tng) (tng) (tng) (tng) (tng) (tng)c. (tng)Class.forName("Com.microsoft.jdbc.sqlServer.SQLServerDriver);
(tng) (tng) (tng) (tng) (tng) (tng) (tng)d. (tng)Class.forName("oracl.jdbc.driver.OracleDriver");
(tng) (tng) (tng) (tng) (tng) (tng) (tng)e. (tng)Class.forName("sun.jdbc.odbc.JdbcOdbcDriver");
(tng) (tng) (tng) (tng)2) (tng)实例化一个Driver
(tng) (tng) (tng) (tng) (tng) (tng) (tng)a. (tng)Driver (tng)drv (tng)= (tng)new (tng)COM.cloudscape.core.RmiJdbcDriver();
2004-9-14 (tng) (tng) (tng) (tng) (tng)星期二?tng) (tng) (tng) (tng) (tng)?br />
1. (tng)建立一个到数据库的q接(步骤?
{：(x)DriverManager调用getConnection(urlString)Ҏ(gu)Q实际上调用的是driver的connect(urlString)Ҏ(gu);
(tng) (tng) (tng) (tng)1) (tng)当一个driver肯定地对应到一个数据库URLQDriverManager建立一个连?
(tng) (tng) (tng) (tng)2) (tng)当没有driver匚wQ返回null然后下一个driver被检?
(tng) (tng) (tng) (tng)3) (tng)假如没有建立q接Q抛Z个SQLExcepiton异常
2. (tng)l常使用的一些JDBC (tng)URL
{：(x)1) (tng)JDBC-ODBC: (tng)jdbc:odbc:<DB>
(tng) (tng) (tng) (tng)2) (tng)Oracle: (tng)jdbc:oracle:oci:@<sid> (tng)or (tng)jdbc:oracle:thin:@<SID>
(tng) (tng) (tng) (tng)3) (tng)Weblogic (tng)MS-SQL: (tng)jdbc:weblogic:mssqlserver4:<DB>@<HOST>:<PORT>
(tng) (tng) (tng) (tng)4) (tng)DB2: (tng)jdbc:db2:MyTest (tng)or (tng)jdbc.db2://localhost:6789/MyTest(需要用户名和密?
3. (tng)Driverq接Ҏ(gu)
{：(x)1) (tng)创徏一个到指定Driver实例的直接调?
(tng) (tng) (tng) (tng)2) (tng)避免一般访问的问题
(tng) (tng) (tng) (tng) (tng) (tng) (tng)Driver (tng)drv (tng)= (tng)new (tng)COM.ibm.db2.jdbc.app.DB2Driver();
(tng) (tng) (tng) (tng) (tng) (tng) (tng)Connection (tng)con (tng)= (tng)null;
(tng) (tng) (tng) (tng) (tng) (tng) (tng)try (tng){con (tng)= (tng)drv.connect("jdbc:db2:MyTest",new (tng)Properties())}
(tng) (tng) (tng) (tng) (tng) (tng) (tng)catch(SQLException (tng)e){}
4. (tng)创徏一个Statement(步骤?
{：(x)1) (tng)Statement的三个接?
(tng) (tng) (tng) (tng) (tng) (tng) (tng)a. (tng)Statement;
(tng) (tng) (tng) (tng) (tng) (tng) (tng)b. (tng)PreparedStatement(l承自Statement);
(tng) (tng) (tng) (tng) (tng) (tng) (tng)c. (tng)CallableStatement(l承自PreparedStatement);
(tng) (tng) (tng) (tng)2) (tng)使用Ҏ(gu)Connection.createStatement()得到一个Statement对象
5. (tng)PreparedStatement对象
{：(x)1) (tng)调用ProparedStatement比statement更ؓ(f)高效;
(tng) (tng) (tng) (tng)2) (tng)l承自Statement;
(tng) (tng) (tng) (tng)3) (tng)语法QPreparedStatement (tng)pstm (tng)= (tng)connection.prepareStatement(sqlString);
6. (tng)CallableStatement对象
{：(x)1) (tng)通过CallableStatement调用数据库中的存储过E?
(tng) (tng) (tng) (tng)2) (tng)l承自PreparedStatement;
(tng) (tng) (tng) (tng)3) (tng)CallableStatement (tng)cstm (tng)= (tng)connection.prepareCall("{call (tng)return_student[?,?]}");
(tng) (tng) (tng) (tng) (tng) (tng) (tng)cstm.setString(1,"8623034");
(tng) (tng) (tng) (tng) (tng) (tng) (tng)cstm.registerOutparameter(2, (tng)Types.REAL);
(tng) (tng) (tng) (tng) (tng) (tng) (tng)cstm.execute();
(tng) (tng) (tng) (tng) (tng) (tng) (tng)float (tng)gpa (tng)= (tng)cstm.getFloat(2);
7. (tng)Statement接口的比?br />{：(x) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng)| (tng)Statement (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng)| (tng)PreparedStatement (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng)| (tng) (tng)CallableStatement
(tng) (tng) (tng) (tng)------------------------------------------------------------------------------
(tng) (tng) (tng) (tng)写代码位|?tng) (tng) (tng)| (tng) (tng) (tng)客户端?tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng)| (tng)客户端?tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng)| (tng) (tng)服务器端
(tng) (tng) (tng) (tng)------------------------------------------------------------------------------
(tng) (tng) (tng) (tng)写代码位|?tng) (tng) (tng)| (tng) (tng) (tng)客户端?tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng)| (tng)服务器端 (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng)| (tng) (tng)服务器端
(tng) (tng) (tng) (tng)------------------------------------------------------------------------------
(tng) (tng) (tng) (tng)~写代码技术?tng)|JavaQSQL操作 (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng)|JavaQSQL操作 (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng)| (tng) (tng)数据库的E序语言Q如PL/SQL
(tng) (tng) (tng) (tng)------------------------------------------------------------------------------
(tng) (tng) (tng) (tng)可配|性?tng) (tng) (tng) (tng) (tng)| (tng) (tng) (tng)高?tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng)|W一ơ高Q以后低 (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng)| (tng) (tng)?br /> (tng) (tng) (tng) (tng)------------------------------------------------------------------------------
(tng) (tng) (tng) (tng)可移植性?tng) (tng) (tng) (tng) (tng)| (tng) (tng) (tng)高?tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng)|假设支持PreparedStatement的话高?tng) (tng) (tng)?br /> (tng) (tng) (tng) (tng)------------------------------------------------------------------------------
(tng) (tng) (tng) (tng)传输效率 (tng) (tng) (tng) (tng) (tng)| (tng) (tng) (tng)低?tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng)|W一ơ低Q以后高 (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng)| (tng) (tng)?br />
8. (tng)执行SQL (tng)Statement(步骤?
{：(x)通过接口Ҏ(gu)SQL语句传输?认的数据库连接，q回l果可能是一个数据表Q可以通过java.sql.ResultSet讉K?br /> (tng) (tng) (tng) (tng)1) (tng)Statement的接口方法：(x)
(tng) (tng) (tng) (tng)a. (tng)executeQuery(sqlString): (tng)执行l定的SQL声明Q返回一个结果集(ResultSet)对象;
(tng) (tng) (tng) (tng)b. (tng)executeUpdate(sqlString): (tng)执行l定的SQL声明Q可以是INSERT、UPDATE或DELETE声明Q也可以是SQL (tng)DDL声明;
(tng) (tng) (tng) (tng)c. (tng)execute(sqlString): (tng)执行l定的SQL声明?br />
9. (tng)处理l果(步骤?
{：(x)1) (tng)使用l果?ResultSet)对象的访问方法获取数?
(tng) (tng) (tng) (tng) (tng) (tng) (tng)a. (tng)next():下一个记?br /> (tng) (tng) (tng) (tng) (tng) (tng) (tng)b. (tng)first():W一个记?br /> (tng) (tng) (tng) (tng) (tng) (tng) (tng)c. (tng)last():最后一个记?br /> (tng) (tng) (tng) (tng) (tng) (tng) (tng)d. (tng)previous():上一个记?br /> (tng) (tng) (tng) (tng)2) (tng)通过字段名或索引取得数据
(tng) (tng) (tng) (tng)3) (tng)l果集保持了(jin)一个指向了(jin)当前行的指针Q初始化位置为第一个记录前?br />
10. (tng)关闭JDBC对象(步骤?
{：(x)1) (tng)首先关闭记录?
(tng) (tng) (tng) (tng)2) (tng)其次关闭声明;
(tng) (tng) (tng) (tng)3) (tng)最后关闭连接对象?br />
11. (tng)数据表和cd应的三种关系Q?br />{：(x)1) (tng)一个表对应一个类;
(tng) (tng) (tng) (tng)2) (tng)一个表对应相关c?
(tng) (tng) (tng) (tng)3) (tng)一个表对应整个cdpd
12. (tng)c间关系的几U表设计Q?br />{：(x)1) (tng)多对一Q?br /> (tng) (tng) (tng) (tng)2) (tng)一对一: (tng)
(tng) (tng) (tng) (tng)3) (tng)一对多Q?br /> (tng) (tng) (tng) (tng)4) (tng)多对多：(x)
13. (tng)SQL数据cd?qing)其相应的Java数据cd
{：(x)SQL数据cd (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng)Java数据cd (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng)说明
(tng) (tng) (tng) (tng)------------------------------------------------------------------
(tng) (tng) (tng) (tng)I(yng)NTEGER或者INT (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng)int (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng)通常是个32位整?br /> (tng) (tng) (tng) (tng)SMALLINT (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng)short (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng)通常是个16位整?br /> (tng) (tng) (tng) (tng)NUMBER(m,n) (tng)DECIMAL(m,n) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng)Java.sql.Numeric (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng)合计位数是m的定点十q制敎ͼ数后面有n位数
(tng) (tng) (tng) (tng)DEC(m,n) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng)Java.sql.Numeric (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng)合计位数是m的定点十q制敎ͼ数后面有n位数
(tng) (tng) (tng) (tng)FLOAT(n) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng)double (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng)q算_ֺ为n位二q制数的点?br /> (tng) (tng) (tng) (tng)REAL (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng)float (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng)通常?2位QҎ(gu)
(tng) (tng) (tng) (tng)DOUBLE (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng)double (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng)通常?4位QҎ(gu)
(tng) (tng) (tng) (tng)CHARACTER(n)或CHAR(n) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng)String (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng)长度为n的固定长度字W串
(tng) (tng) (tng) (tng)VARCHAR(n) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng)String (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng)最大长度ؓ(f)n的可变长度字W串
(tng) (tng) (tng) (tng)BOOLEAN (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng)boolean (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng)布尔?br /> (tng) (tng) (tng) (tng)DATE (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng)Java.sql.Date (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng)Ҏ(gu)具体讑֤而实现的日历日期
(tng) (tng) (tng) (tng)TIME (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng)Java.sql.Time (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng)Ҏ(gu)具体讑֤而实现的时戳
(tng) (tng) (tng) (tng)TIMESTAMP (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng)Java.sql.Timestamp (tng) (tng) (tng) (tng) (tng) (tng)Ҏ(gu)具体讑֤而实现的当日日期和时?br /> (tng) (tng) (tng) (tng)BLOB (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng)Java.sql.Blob (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng)二进制大型对?br /> (tng) (tng) (tng) (tng)CLOB (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng)Java.sql.Clob (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng)字符大型对象
(tng) (tng) (tng) (tng)ARRAY (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng)Java.sql.Array
(tng) (tng) (tng) (tng)
2004-9-15 (tng) (tng) (tng) (tng) (tng)星期三?tng) (tng) (tng) (tng) (tng) (tng)?br />
1. (tng)元数?br />{：(x)关于数据的信息，例如cd或者容量。通过JDBC (tng)API可以讉KQ?br /> (tng) (tng) (tng) (tng)1) (tng)数据库元数据;
(tng) (tng) (tng) (tng) (tng) (tng) (tng)a. (tng)使用connection.getMetadataҎ(gu)q回DataMetaData引用
(tng) (tng) (tng) (tng) (tng) (tng) (tng)b. (tng)能够使用isReadOnly此类Ҏ(gu)获取信息
(tng) (tng) (tng) (tng)2) (tng)l果集元数据;
(tng) (tng) (tng) (tng) (tng) (tng) (tng)a. (tng)使用ResultSet.getMetadataҎ(gu)q回ResultSetMetaData引用
(tng) (tng) (tng) (tng) (tng) (tng) (tng)b. (tng)能够使用getColumnCount此类Ҏ(gu)获取信息
2. (tng)事务处理
{：(x)1) (tng)一pd的动作作Z个不可分的操?
(tng) (tng) (tng) (tng)2) (tng)JDBC (tng)API中用事务处理步骤：(x)
(tng) (tng) (tng) (tng) (tng) (tng) (tng)a. (tng)用false作ؓ(f)参数调用setAutoCommitҎ(gu);
(tng) (tng) (tng) (tng) (tng) (tng) (tng)b. (tng)执行一或多个关于数据库的操?
(tng) (tng) (tng) (tng) (tng) (tng) (tng)c. (tng)调用commitҎ(gu)完成改变;
(tng) (tng) (tng) (tng) (tng) (tng) (tng)d. (tng)恢复上次提交后的改变Q调用rollbackҎ(gu).
(tng) (tng) (tng) (tng) (tng) (tng) (tng)try
(tng) (tng) (tng) (tng) (tng) (tng) (tng){
(tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng)con.setAutoCommit(false);
(tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng)Statement (tng)stm (tng)= (tng)con.createStatement();
(tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng)stm.executeUpdate("insert (tng)into (tng)student(name, (tng)age, (tng)gpa) (tng)values('gzhu', (tng)30, (tng)4.8)");
(tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng)stm.commit();
(tng) (tng) (tng) (tng) (tng) (tng) (tng)}
(tng) (tng) (tng) (tng) (tng) (tng) (tng)catch(SQLException (tng)e)
(tng) (tng) (tng) (tng) (tng) (tng) (tng){
(tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng)try
(tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng){
(tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng)con.rollback();
(tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng)}
(tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng)catch(Exception (tng)e)
(tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng){
(tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng)}
(tng) (tng) (tng) (tng) (tng) (tng) (tng)}
3. (tng)q发控制
{：(x)1) (tng)讄隔离U别Ҏ(gu)QsetTransactionIsolation
(tng) (tng) (tng) (tng)2) (tng)隔离U别?rn)态变?br /> (tng) (tng) (tng) (tng) (tng) (tng) (tng)a. (tng)TRANSACTION_NONEQ只ȝ数据字典;
(tng) (tng) (tng) (tng) (tng) (tng) (tng)b. (tng)TRANSACTION_READ_UNCOMMITTEDQ只L提交数据;
(tng) (tng) (tng) (tng) (tng) (tng) (tng)c. (tng)TRANSACTION_READ_COMMITTEDQ只L提交数据;
(tng) (tng) (tng) (tng) (tng) (tng) (tng)d. (tng)TRANSACTION_REPEATABLE_READQ重复读取数?
(tng) (tng) (tng) (tng) (tng) (tng) (tng)e. (tng)TRANSACTION_SERIALIZABLEQ无论做什么操作都不许别h动?br /> (tng) (tng) (tng) (tng)3) (tng)CZQcon.setTransactionIsolation(Connection.TRANSACTION_READ_UNCOMMITTED);
4. (tng)JDBC (tng)2.0 (tng)应用E序~程接口增强功能
{：(x)1) (tng)ResultSet增强Q?br /> (tng) (tng) (tng) (tng) (tng) (tng) (tng)a. (tng)可以回卷;
(tng) (tng) (tng) (tng) (tng) (tng) (tng)b. (tng)可以修改;
(tng) (tng) (tng) (tng) (tng) (tng) (tng)讄CZQStatement (tng)stm (tng)= (tng)con.createStatement(ResultSet.TYPE_SCROLL_SENSITIVE,ResultSet.CONCUR_UPDATABLE);
(tng) (tng) (tng) (tng)2) (tng)Statement增强?jin)批量修改能?batch (tng)updates);
(tng) (tng) (tng) (tng)3) (tng)更高U的数据cd(例：(x)Struct)?br />
5. (tng)JDBC (tng)2.0标准扩展
{：(x)1) (tng)JNDI(Java (tng)Naming (tng)and (tng)Directory (tng)I(yng)nterface): (tng)解决L状态下Object的查?
(tng) (tng) (tng) (tng)2) (tng)q接池：(x)在内存(sh)保存?sh)(jin)一个数据库q接Q不需要注册驱动器Q提高性能的重要方法?img src ="http://www.tkk7.com/coolfiry/aggbug/78860.html" width = "1" height = "1" />
]]>
CZ1Q将两个class文g存档C个名为?classes.jar' (tng)的存文件中Q?br /> (tng)& nbsp; (tng) (tng) (tng) (tng) (tng)jar (tng)cvf& nbsp;classes.jar (tng)Foo.class (tng)Bar.class
CZ2Q用一个存在的清单QmanifestQ文件?mymanifest' (tng)?tng)foo/& nbsp;目录下的所?br /> (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng)文g存C个名? (tng)'classes.jar' (tng)的存文件中Q?br /> (tng) (tng) (tng) (tng) (tng) (tng) (tng)jar (tng)cvfm (tng) classes.jar (tng)mymanifest (tng)-C (tng)foo/ (tng).
来个例子试试看Q?br />我们只有一个HelloWorldQ如下：(x)
public& nbsp; (tng)class (tng) (tng)HelloWorld{
(tng)public& nbsp;static (tng)void (tng)main(String[] (tng)args){
(tng)System.out.println(“Hi, (tng)Hello (tng)World!?;
}
}
我将q个java文g存到C盘跟目录下，okQ接下来Q?br />在先前打开的命令提C符?跌{到C盘提C符?Q我们输入javac (tng)HelloWorld.javaQ然后l输入：(x)jar (tng)& nbsp;cvf (tng) (tng)hello.jar (tng) (tng)HelloWorld.classQ回车后M的C盘看看，多了(jin)什么，没错 (tng)hello.jar (tng)?br />基本的步骤我们现在都知道?jin)，你可以自己去试一下随着jar后面的参数的不同Q结果有什么变化?br />紧接着我们看看如何q行我们的jar包?br />在进入正题(sh)前，你要先打开我们刚刚做好的jar包看看，多了(jin)什么呢QMETA-INF目录Q再看看里面是什么，q有一个MANIFEST.MF文g是不是？用文本编辑器(我这里是UltraEdit)打开它看看：(x)
Manifest-Version: (tng) 1.0
Created-By: (tng)1.4.2 (tng)(Sun (tng)Microsystems& nbsp;Inc.)
是q样。这里我们对它进行修改，加一句：(x)Main-Class: (tng) HelloWorld (tng)(在第三行)。这个就是我们之前写的那个类Q也是我们的入口类。也卻I
Manifest -Version: (tng)1.0
Created-By: (tng)1.4.2 (tng)(Sun& nbsp;Microsystems (tng)I(yng)nc.)
Main-Class: (tng)HelloWorld< BR>接下来，我们在命令提C符里执行：(x)
jar (tng)umf (tng) MANIFEST.MF (tng)app.jar
q样我们使用?jin)我们自qMANIFEST.MF文g对原来默认的q行?jin)更新。你不妨可以再进ȝ看是不是M?jin)Main-Class: (tng)HelloWorldq一句?br />OkQ这个最后的一步了(jin)Q来验证我们做的一切，在命令提C符中输入：(x)
java (tng)-jar (tng)hello.jar (执行)
出现?jin)什么，――Hi, (tng)Hello (tng)World!
我们再来看看 jar文g在tomcat中发布，注意Q在tomcat中我们就不能再用jarq种格式Q而改war格式Q它是专门用于web应用的，其实整个q程下来基本上和jar是类似的Q?br />先准备我们要打包的资源?br />扑ֈ存放tomcat的webapps目录Q进到其中，新徏一个文件夹Q这里命名ؓ(f)helloQ再q去新徏WEB-INF文g夹，再进L建classes文g夹，此时我们也将我们唯一的servletQ?HelloWorld.java攑ֈq里Q在与classes目录同下徏立一文gweb.xml。OkQ目前我们初步徏立了(jin)一个简单的web应用?
q是HelloWorld.javaQ?br />import (tng)java.io.*;< BR>import (tng)javax.servlet.*;
import (tng)javax.servlet.http.*;
public (tng)class (tng)HelloWorld (tng)extends& nbsp;HttpServlet (tng){
(tng)public (tng)void (tng) doGet(HttpServletRequest (tng)req, (tng)HttpServletResponse (tng) res)
(tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng)& nbsp; (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng) (tng)& nbsp; (tng)throws (tng)ServletException, (tng)I(yng)OException& nbsp;{
(tng) (tng)res.setContentType("text/html");
(tng) (tng)PrintWriter (tng)out (tng)= (tng)res.getWriter ();
(tng) (tng)out.println("<HTML>");< BR> (tng) (tng)out.println("<HEAD><TITLE& gt;Hello, (tng)World!</TITLE></HEAD>");< BR> (tng) (tng)out.println("<BODY>");
& nbsp; (tng)out.println("Hello, (tng)World!");
(tng) (tng)out.println("</BODY></HTML>");
(tng)}
}//end (tng)here!
对它~译。下面是web.xmlQ?lt; BR><?xml (tng)version="1.0" (tng)encoding="ISO-8859-1"?>
<!DOCTYPE (tng)web-app (tng)PUBLIC
(tng) (tng)'-//Sun (tng)Microsystems, (tng)I(yng)nc.//DTD (tng)Web (tng)Application (tng)2.3//EN'
(tng) (tng)'
http://java.sun.com/j2ee/dtds/web-app_2_3.dtd&< /FONT>#39;><web-app>
(tng) (tng)<servlet>
(tng) (tng) (tng) (tng)<servlet-name>hello</servlet-name& gt;
(tng) (tng) (tng) (tng)<servlet-class& gt;HelloWorld</servlet-class>
(tng) (tng) </servlet>
(tng) (tng)<servlet-mapping& gt;
(tng)<servlet-name>hello</servlet- name>
(tng)<url-pattern>/HelloWorld& lt;/url-pattern>
(tng) (tng)</servlet-mapping& gt;
</web-app>
开始压~，形成war档：(x)
在命令提C符下进到先前创制的hello目录下，执行 (tng)jar (tng) (tng)cvf (tng) (tng)hello.war (tng) (tng)* (tng)Q我们便得到hello.war。将它拷贝至 webapps目录下，okQ来看最后一步，打开tomcat的目录conf中的server.xmlQ加入：(x)
(tng) (tng)<Context (tng)path="/hello" (tng)docBase="hello.war"& nbsp;debug="0"
(tng) (tng) (tng) (tng)reloadable ="true"/>
大功告成Q运行它Q启动tomcatQ后在浏览器中输?img src="http://www.matrix.org.cn/images/small/url.gif" align="absmiddle" />http://localhost:8080/hello/HelloWorldQ有?jin)吗Q?br />最后，如果你想用ant来完成以上的打包zdQ下面就告诉你：(x)
对于jar来说。在build.xml 中，
(tng)<target (tng)name="jar">< BR> (tng) (tng)<jar (tng)destfile="${app_home}/hello.jar"& gt;
(tng) (tng) (tng)<fileset (tng)dir=" ${dest}" (tng)includes="**"/>
(tng) (tng)& nbsp; (tng) (tng) (tng)<!--fileset (tng)dir="${dest} " (tng)includes="**/action.properties"/-->
(tng) (tng) (tng) (tng)</jar>
(tng)& lt;/target>
对于warQ?br /><war& nbsp;warfile="hello.war" (tng)webxml="./WEB-INF/web.xml">
(tng) (tng) (tng) (tng)<fileset (tng)dir="html"/& gt;
(tng) (tng) (tng) (tng)<lib (tng) dir="lib/">
(tng) (tng) (tng) (tng)& nbsp; (tng) (tng) (tng)<exclude (tng)name="oracle*.jar"/& gt;
(tng) (tng) (tng) (tng)</lib>
(tng) (tng) (tng) (tng)<classes (tng) dir="build/servlets">
(tng) (tng) (tng)& nbsp; (tng) (tng) (tng) (tng) (tng)<include& nbsp;name="**/*.class"/>
(tng) (tng)</classes& gt;
</war> (tng)
好了(jin)Q就q么多，希望对你有点帮助。：(x)Q?
我上传了(jin)上面打过的两个包Qhello.jar和hello.war?img src="http://www.matrix.org.cn/images/small/download.gif" align="absmiddle" border="0" height="16" width="16" />?点击下蝲?/font>
?点击下蝲?/font>W一rar文g对应的是hello.jar,下蝲后将其名改ؓ(f) hello.jar
W二rar文g对应hello.warQ下载后改ؓ(f)hello.war?br />q是׃上传不了(jin) jar格式和war格式的文Ӟ你只好照我上面说的去做了(jin) (tng)Q）(j)
补充Q?br /> ############
jar基本操作Q?br />############
1.& nbsp;创徏jar文g
(tng) (tng)jar (tng)cf (tng)jar- file (tng)input-file(s)
c---want (tng)to (tng)Create& nbsp;a (tng)JAR (tng)file.
f---want (tng)the (tng) output (tng)to (tng)go (tng)to (tng)a (tng)file (tng) rather (tng)than (tng)to (tng)stdout.
eg: (tng)1) jar (tng)cf (tng)myjar.jar (tng)query_maintain_insert.htm< BR> (tng) (tng) (tng) (tng)2)jar (tng)cvf (tng) myjar.jar (tng)query_maintain_insert.htm
(tng) (tng) (tng) (tng) (tng) (tng)v---Produces (tng)verbose(详细? (tng)output.
(tng) (tng) (tng) (tng)3)jar& nbsp;cvf (tng)myjar.jar (tng)query_maintain_insert.htm (tng)mydirectory< BR> (tng) (tng) (tng) (tng)4)jar (tng)cv0f (tng) myjar.jar (tng)query_maintain_insert.htm (tng)mydirectory
(tng) (tng) (tng) (tng) (tng) (tng)0---don't& nbsp;want (tng)the (tng)JAR (tng)file (tng)to (tng)be& nbsp;compressed.
(tng) (tng) (tng) (tng)5)jar& nbsp;cmf (tng)MANIFEST.MF (tng)myjar.jar (tng)yahh.txt
(tng) (tng) (tng) (tng) (tng) (tng)m---Used& nbsp;to (tng)include (tng)manifest (tng)information (tng) from (tng)an (tng)existing (tng)manifest (tng)file.
(tng) (tng) (tng) (tng)6)jar (tng)cMf (tng)MANIFEST.MF& nbsp;myjar.jar (tng)yahh.txt
(tng) (tng) (tng)& nbsp; (tng) (tng)M---the (tng)default (tng)manifest (tng) file (tng)should (tng)not (tng)be (tng)produced.
(tng) (tng) (tng) (tng)7)jar (tng)cvf (tng)myjar.jar& nbsp;*
(tng) (tng) (tng) (tng) (tng) (tng) *---create (tng)all (tng)contents (tng)in (tng)current& nbsp;directory.
2. (tng)察看jar文g
(tng)& nbsp;jar (tng)tf (tng)jar-file
t---want (tng)to& nbsp;view (tng)the (tng)Table (tng)of (tng)contents (tng) of (tng)the (tng)JAR (tng)file.
eg: (tng)1)jar& nbsp;vft (tng)yahh.jar
(tng) (tng) (tng) (tng) (tng) (tng)v---Produces (tng)verbose(详细? (tng) output.
3. (tng)提取jar文g
(tng) (tng) jar (tng)xf (tng)jar-file (tng)[archived-file(s)]
x- --want (tng)to (tng)extract (tng)files (tng)from (tng) the (tng)JAR (tng)archive.
eg: (tng)1)jar (tng)xf& nbsp;yahh.jar (tng)yahh.txt(仅提取文件yahh.txt)
(tng)& nbsp; (tng) (tng)2)jar (tng)xf (tng)yahh.jar (tng)alex/yahhalex.txt (仅提取目录alex下的文gyahhalex.txt)
(tng) (tng) (tng)& nbsp;3)jar (tng)xf (tng)yahh.jar(提取该jar包中的所有文件或目录)
4. (tng)修改Manifest文g
(tng) (tng)jar (tng) cmf (tng)manifest-addition (tng)jar-file (tng)input-file(s)< BR>m---Used (tng)to (tng)include (tng)manifest (tng)information& nbsp;from (tng)an (tng)existing (tng)manifest (tng)file.< BR>5. (tng)更新jar文g
(tng) (tng)jar (tng) uf (tng)jar-file (tng)input-file(s)
u---want (tng)to (tng)update (tng)a
]]>
该文章提供了(jin)打包Java code的几U方法，我们会(x)探讨Java manifest 文gQ给出用于管理JAR文g所依赖文g、估计跨q_发布所需的CLasspath的合适方?我也?x)解释如何用manifest包版本特性来认包的兼容?..
什么是JAR文gQ?/b>
在开发过E中Q我们可以直接用Java class文g来运行程序，但这q不是一个好方式Q好在Java 提供?JAR(Java Archive)文g来提供发布和q行?br />
jar 文g实际上是class 文g的ZIP压羃存Q这U格式被q泛使用Q因此易与用，有很多中工具可以操作q种格式的文件。也正是因ؓ(f)q个原因Qjar文g本nq不能表达所包含应用E序的标{信息?br />
Manifest 因此得以出现
Z(jin)要提供存的标签信息Qjar 文g指定?jin)一个特定目录来存放标签信息QMETA-INF 目录Q其中我们来x(chng)该目录中的MANIFEST.MF文gQ他是JAR的manifest文gQ他包含?jin)JAR文g的内Ҏ(gu)qͼq在q行时向JVM? 供应用程序的信息Q大多数JAR文g含有一个默认生成的manifest 文g,执行JAR命o(h)或用zip工具Q都可以产生?br />
如果是由jar命o(h)产生?manifest 文gQŞ?
Manifest-Version: 1.0
Created-By:1.4.0-beta
(Sun Microsystems Inc.)
q些信息没甚么用,仅仅告诉我们使用的是1.0的manifest文g,W一行定义manifest的格式，W二行说明?SUN 的JDK1.4的jar工具生成该文Ӟ如果manifest文g是由其他 Q如antQ?创徏的，那将?x)出?“Created-By: Ant 1.2?之类的内容，如果你是自己创徏manifest文gQ你可以加入自己的一些相关信?
基础格式
manifest 文g的格?是很单的Q每一行都?名－?对应?属性名开_(d)接着?":" Q然后是属性|每行最?2个字W，如果需要增加，你可以在下一行箋(hu)行，l行以空格开_(d)以空格开头的行都?x)被视?f)前一行的l行?br />
所有在开头的属性都是全局的，你也可以定义特定class 或package的属性，E后介l这U?br />
把manifest文g插入JAR文g
使用 m 选项Q把指定文g名的manifest文g 传入Q例?br /> jar cvfm myapplication.jar myapplication.mf -C classdir
如果你用ant来创建时Q在ant 的build.xml 加入如下条目
<target name="jar">
<jar jarfile ="myapplication.jar"
manifest="myapplication.mf">
<fileset dir="classdir"
includes="**/*.class"/>
</jar>
</target>
q行JavaE序
现在我们来体验一下manifest文g的作用，如果现在我们有一个Java 应用E序打包在myapplication.jar中， main class?com.example.myapp.MyAppMain Q那么我们可以用以下的命令来q行
java -classpath myapplication.jar com.example.myapp.MyAppMain
q显然太ȝ(ch)?jin)，现在我们来创qmanifest文gQ如下：(x)
Manifest-Version: 1.0
Created-By: JDJ example
Main-Class: com.example.myapp.MyAppMain
q样我们可以用如下的命o(h)来运行程序了(jin)Q（明显单多?jin)，也不会(x)造成无谓的拼写错误）(j)
java -jar myapplication.jar
理JAR的依赖资?/b>
很少Java应用?x)仅仅只有一个jar文gQ一般还需?其他cd。比如我的应用程序用C(jin)Sun ?Javamail classes Q在classpath中我需要包含activation.jar ?mail.jar,q样在运行程序时,相比上面的例?我们要增加一?
java -classpath mail.jar:activation.jar -jar myapplication.jar
在不同的操作pȝ?jar包间的分隔符也不一P在UNIX用“：(x)”，在window中?“；”，q样也不方便
同样Q我们改写我们的manifest文gQ如?br /> Manifest-Version: 1.0
Created-By: JDJ example
Main-Class: com.example.myapp.MyAppMain
Class-Path: mail.jar activation.jar
Q加入了(jin)Class-Path: mail.jar activation.jarQ用I格分隔两个jar包）(j)
q样我们仍然可以使用和上例中相同的命令来执行该程序：(x)
java -jar myapplication.jar
Class-Path属性中包含?jin)用I格分隔的jar文gQ在q些jar文g名中要对特定的字W用逃逸符Q比如空|要表C成"%20"Q在路径的表 CZQ都采用?”来分隔目录Q无论是在什么操作系l中Q?即在window?Q而且q里用的是相对\径（相对于本w的JAR文gQ：(x)
Manifest-Version: 1.0
Created-By: JDJ example
Main-Class: com.example.myapp.MyAppMain
Class-Path: ext/mail.jar ext/activation.jar
Multiple Main ClassesQ多ȝQ?br />
q有一UMultiple Main Classes情况Q如果你的应用程序可能有命o(h)行版? 和GUI版本Q或者一些不同的应用却共享很多相同的代码Q这时你可能有多个Main ClassQ我们徏议你采取q样的策略：(x)把共享的cL成lib包，然后把不同的应用打成不同的包Q分别标志主c：(x)如下
Manifest for myapplicationlib.jar:
Manifest-Version: 1.0
Created-By: JDJ example
Class-Path: mail.jar activation.jar
Manifest for myappconsole.jar:
Manifest-Version: 1.0
Created-By: JDJ example
Class-Path: myapplicationlib.jar
Main-Class: com.example.myapp.MyAppMain
Manifest for myappadmin.jar:
Manifest-Version: 1.0
Created-By: JDJ example
Class-Path: myapplicationlib.jar
Main-Class: com.example.myapp.MyAdminTool
在myappconsole.jar ?myappadmin.jar的manifest文g中分别注明各自的 Main Class
Package Versioning
完成发布后，如果使用者想?jin)?Q哪些代码是谁的Q目前是什么版本？使用什么版本的cdQ解决的Ҏ(gu)很多 Qmanifest提供?jin)一个较好的Ҏ(gu)Q你可以在manifest文g中描q每一个包的信息?br />
Java U承?jin)实现说明与描述分离的原则，package 的描q?定义?jin)package 是什么，实现说明 定义?jin)谁提供了(jin)描q的实现Q描q和实现包含 名、版本号和提供者。要得到q些信息Q可以查看JVM的系l属性（使用 java.lang.System.getProperty() Q?br />
在manifest文g中，我可以ؓ(f)每个package定义描述和实现版本，声明名字Qƈ加入描述属性和实现属性，q些属性是
Specification-Title
Specification-Version
Specification-Vendor
Implementation-Title
Implementation-Version
Implementation-Vendor
当要提供一个类库或~程接口Ӟ描述信息昑־是很重要Q见以下范例Q?br />
Manifest-Version: 1.0
Created-By: JDJ example
Class-Path: mail.jar activation.jar
Name: com/example/myapp/
Specification-Title: MyApp
Specification-Version: 2.4
Specification-Vendor: example.com
Implementation-Title: com.example.myapp
Implementation-Version: 2002-03-05-A
Implementation-Vendor: example.com
Package Version 查询
在manifest文g中加入package描述后，可以用Java提供的java.lang.Package classq行Package 的信息查询，q里列D3个最基本的获取package object的方?br />
1.Package.getPackages():q回pȝ中所有定义的package列表
2.Package.getPackage(String packagename):按名q回package
3.Class.getPackage():q回l定class所在的package
使用者这Ҏ(gu)可以动态的获取package信息.
需要注意的是如果给定的package中没有class被加?则也无法获得package 对象
Manifest 技?/b>
L以Manifest-Version属性开?br />
每行最?2个字W，如果过的化Q采用箋(hu)?br />
认每行都以回Rl束Q否则改行将?x)被忽?br />
如果Class-Path 中的存在路径Q?/"分隔目录Q与q_无关
使用I分隔d性和package属?br />
使用"/"而不?."来分隔package 和class ,比如 com/example/myapp/
class 要以.classl尾Qpackage 要以 / l尾
]]>
摘要:
q日, Sun 宣布收购 JRuby 目.Sunl于开始表露出让不仅仅是Javaq行在JVM上的兴趣?(tng)
q日, Sun 宣布收购 JRuby 目.
Sunl于开始表露出让不仅仅是Javaq行在JVM上的兴趣?
q日,SUNq出?jin)重要的一?
Charles Nutter, JRuby 的核?j)开发者之一, 宣布: Sun 已经整体收购?jin)JRuby 目. 他与JRuby的另外一个核?j)开发?br />Thomas Enobo 都将?x)加入Sun.
从这ơ动作看的出来Ruby在Sun战略中的C, (tng) (tng)看来Ruby很有可能成ؓ(f)JVM支持的第一个非Java语言.
动态语a, 已经不遥q了(jin).
官方站点:
http://jruby.sourceforge.net/
(http://www.matrix.org.cn/resource/news/JRuby+Sun_954.html)
Sunl于开始表露出让不仅仅是Javaq行在JVM上的兴趣?
q日,SUNq出?jin)重要的一?
Charles Nutter, JRuby 的核?j)开发者之一, 宣布: Sun 已经整体收购?jin)JRuby 目. 他与JRuby的另外一个核?j)开发?br />Thomas Enobo 都将?x)加入Sun.
从这ơ动作看的出来Ruby在Sun战略中的C, (tng) (tng)看来Ruby很有可能成ؓ(f)JVM支持的第一个非Java语言.
动态语a, 已经不遥q了(jin).
官方站点:
http://jruby.sourceforge.net/
(http://www.matrix.org.cn/resource/news/JRuby+Sun_954.html)
]]>
]]>