article - Kenyth Zeng on Diigo

16 Dec 09

15 Dec 09

Buffer和cache的区别是什么？ - delphij's Chaos

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cache concept blog article comparison

14 Dec 09

探索 CouchDB

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db key-value article CouchDB

面向文档的数据库中根本不存在表、行、列或关系。
这并不意味着不能从 CouchDB 数据库获取一组关系数据。一个称为视图的特性允许您为没有在数据库中定义的文档创建一种任意关系。这意味着您能够获得典型的 SQL 联合查询的所有好处，但又不需要在数据库层预定义它们的关系。
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- CouchDB 的目的并不是替换关系数据库，而是为那些更适合使用面向文档模型（而不是传统的关系数据模型）的项目提供一种选择，比如 wikis、博客和文档管理系统。
- B-树储存引擎
- 它依赖于使用视图创建文档之间的任意关系，以及提供聚合和报告特性。使用 Map/Reduce 计算这些视图的结果
- CouchDB 中的 Map/Reduce 特性生成键/值对，CouchDB 将它们插入到 B-树引擎中并根据它们的键进行排序。这就能通过键进行高效查找，并且提高 B-树中的操作的性能。
- 在 CouchDB 中没有锁机制，它使用的是多版本并发性控制（Multiversion concurrency controlMVCC）— 它向每个客户机提供数据库的最新版本的快照。这意味着在提交事务之前，其他用户不能看到更改。许多现代数据库开始从锁机制前移到 MVCC，包括 Oracle（V7 之后）和 Microsoft® SQL Server 2005 及更新版本。
- 包含元数据（关于数据的数据），比如惟一的文档 ID 和修改号。文档字段可以包含各种类型的数据，比如文本字符串、数字和布尔值（true/false）等。
- 当更改 CouchDB 文档时，这些更改实际上并不是附加在原来的文档之上，而是创建整个文档的一个新版本，即修订。
- 不过，如果一个客户机保存了所有更改时，另一个客户机在尝试保存更改时将收到一个编辑冲突。可以通过加载更新版本的文档来解决该冲突，然后重新进行编辑并再次保存。
- 想一下关系数据库，对于每个应用程序，严格定义的表之间的关系对于为数据赋予意义至关重要。不过，当要求实现更高的性能时，则需要创建物化视图来反规范化（de-normalize）数据。在很多情况下，面向文档数据库采用相反的方法处理事情。它将数据储存在一个平面地址空间中，这就像一个完全反规范化的数据仓库。然后它提供一个视图模型为数据添加结构，因此能够聚合数据得出有用的含义。
- CouchDB 在 Web 应用程序、iPhone 应用程序和 Facebook 应用程序中越来越流行。

08 Dec 09

InfoQ: SproutCore: An HTML 5 Application Framework

www.infoq.com/...sproutcore-1-0 - Preview

HTML5 javascript framework article interview

InfoQ: Virtual Panel: Evolution of JavaScript Frameworks for HTML 5

www.infoq.com/js-for-h5 - Preview

javascript framework HTML5 support compatibility discussion article

HTML 5 introduces a number of new Javascript APIs.
2D drawing API which can be used with a new canvas
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- A history API that exposes the browsing history and allows pages to add to it to facilitate better back-button support in AJAX applications.
- Cross-document messaging
- A drag & drop API to use in combination with a draggable attribute.
- A new network API to enable web applications to communicate with each other on local area networks
- Applications like Mozilla Labs' Bespin point to the need of non-DOM-centric development, and I've always thought of the DOM as a tool for JavaScript developers, rather than the approach some take, where if you can't represent a change withing the DOM, it shouldn't be done in the browser.
- Flash/Flex/AIR is a good example of an "alternative model" that thrives as part of (and in parallel to) the HTML/DOM/CSS web.

InfoQ: JavaRebel: Dynamic Classloading in the JVM

www.infoq.com/...javarebel - Preview

classloader JRebel article

JavaRebel brings Ruby and PHP style dynamic reloading of classes to Java.
This includes adding and removing both methods and fields and the only forbidden changes are to ‘extends’ and ‘implements’ clauses

03 Dec 09

幂律分布-搜狐财经

business.sohu.com/...n268436291.shtml - Preview

20-80 article analysis social LongTail starred

也请注意由于少数几位摄影者不成比例的提交量，3/4的摄影者所提交照片数量低于平均值。这个模式在博客、邮件组等社会性媒体中普遍呈现。
维基百科用户中提交过内容的不足2%，却足以为数百万用户创造深远的价值。如果考虑过减少这些不平等的话，推动维基百科发展的自发的劳动分工就不可能了。
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- 绝大多数大型社会实验都推动了利用某种不平等现象而不是限制它。
- 因为大型社会系统不应被理解为某种“平均”用户行为的简单聚合，所谓“平均”从来都不存在。
- 以维基百科的文章编辑为例，你可以料到排名第二的最活跃用户的编辑量只及第一名编辑量的一半，而排名第10的只做了后者的1/10。这也是所谓“80/20法则”背后的形态。
- 他发现在他所研究的每个国家其财富都呈幂律分布，这个模式如此普遍，他因而称之“可预料的不均衡”（a predictable imbalance）。
- 20世纪早期意大利经济学家维弗雷多·帕累托（Vilfredo Pareto）
- 这个形态同我们熟悉的钟形曲线分布（bell curve distribution）都很不一样。钟形曲线分布也叫正态分布
- 由于他们的活跃程度，对“平均”参与的任何测量失去了意义。从少数极度活跃的成员到一大群几乎不活动成员之间是陡峭的下跌，尽管平均值很容易计算，却几乎完全不具代表性。

06 Nov 09

Class Loading in Java: Time to Add Dynamicity? | Javalobby

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JRebel hot deploy java discussion .net jvm classloader class article

But not everything can be reloaded by JavaRebel: No reloads with class hierarchy change are possible.
no schema changes are allowed.
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- Our «irritating little» friend Ruby has this idea of open classes: you may change a class at runtime by adding new methods. This proves that it's possible to do ad-hoc changes.
- Dynamic languages pay a huge performance hit for the ability to update classes dynamically.
- http://classworlds.codehaus.org/
- AFAIK .NET does not reload code, it does full redeploy juts like Java, just application start usually will take less.
- In many cases if you have problems with proxies adding "-Drebel.forbid_bypass=true" will help.
- So if we could only have a jvm-server that could integrate all types of similar jar in the memory.
- They're all compiled with offsets, not labels. When you say "getTitle", the JVM knows the offset within the object structure to the "title" instance variable (if you had, say, 3 instance variables, title being the 3rd slot, all class references (vs, say, char or int),
- Most dynamic languages written on top of the JVM, for example, don't use Java Classes at all for their instances, because they're so rigid.

How JavaRebel Saves Development Time | Javalobby

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JRebel java hot deploy classloader jvm debug dev article how-something-work starred

When debugging through my code in Eclipse, it’s nice to make a change and see that reflected in the running instance straight away with HotSwap.
I’ve often wondered why this is the case with Java when dynamic languages and .NET can handle this quickly.
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- Finally, OSGi is another approach to take - by splitting your application into smaller modules, it can make the redeployment seem faster.
- With JavaRebel, it’s conceivable that I can start up my debug session and nicely interweave my code changes into the running instance, without anything unexpected happening.
- Why doesn’t this exist already in Java? And how has .NET managed to have this from day one?
- The tricky part in reloading object-oriented code is preserving the object state intact.
- However web development frameworks in .NET are designed around stateless and/or isolated classes so turnaround is usually instantaneous. However I’d assume that writing a complicated business app would run into same problem as Java at some point.
- The need to support class code, structure and layout changes would mean significant compromises in the JVM Just-In-Time compiler. Specifically you’d have to do dependency analysis between classes and make the method lookup and calls more dynamic than they currently are. This would decrease performance, or at least further complicate the design of the JVM. These compromises are already present in dynamic languages VMs, which makes it easy to implement such features there.
- We extend their APIs with an ability to inject and override classes, resources and web resources in the running web applications. We then interpret the rebel.xml file provided by the user to override the deployed classes and resources with the ones found from the project workspace.
- To reload the actual classes we build a kind of our own Just-In-Time compiler, which intercepts loading of every class and rewrites them in a way that makes reloading possible.

04 Nov 09

Understanding Network Class Loaders

URLClassLoader

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network classloader url security article java starred introduction

The mechanism that enabled such dynamic loading is a class loader, which is one of the cornerstones of Java dynamism.
The process of combining the code into an executable native code is called linking - the merging of separately compiled code with shared library code to create an executable application.
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- Any URL that ends with a '/' is assumed to refer to a directory, otherwise the URL is assumed to refer to a JAR file which will be opened as needed.
- One way to protect against such attacks is by using a security manager, which is not automatically installed when an application is running.
- prompt> java -Djava.security.manager MyLoader2
- The default security manager, however, doesn't allow your application to create its own class loader.
- Such a security policy allows you to state, using grant clauses, what sorts of actions a Java program can and cannot perform.
- A thread's context class loader is, by default, set to the context class loader of the thread's parent.

Discover the secrets of the Java Serialization API

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java serialization starred api article persistence

That means we could easily transfer a flattened object across a network wire and have it be rebuilt on the other side!
the class file must be accessible from the system in which the restoration occurs
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- In other words, the object's class file and methods are not saved; only the object's state is saved.
- what if we have a class that contains an instance of Thread? In that case, can we ever persist objects of that type? The answer is yes, as long as we tell the serialization mechanism our intentions by marking our class's Thread object as transient.
- The bottom line: you must mark transient any field that
  either cannot be serialized or any field you do not want serialized.
- That does not make for a seamless mechanism,
  something the Java Serialization API promises developers.
- developers can enhance the normal process by
  providing two methods inside their class files. Those methods are:
  
  private void writeObject(ObjectOutputStream out) throws IOException;
  private void readObject(ObjectInputStream in) throws IOException, ClassNotFoundException;
  
  Notice that both methods are (and must be) declared private, proving
  that neither method is inherited and overridden or overloaded.
- 230   private void readObject(ObjectInputStream in) throws IOException, ClassNotFoundException
  
  240   {
  
  250     // our "pseudo-constructor"
  
  260     in.defaultReadObject();
  
  270     // now we are a "live" object again, so let's run rebuild and start
  
  280     startAnimation();
  
  290
  
  300   }
- Those methods work because the call to ObjectOutputStream.writeObject()
  kicks off the serialization protocol. First, the object is checked to ensure it
  implements Serializable and then it is checked to see whether
  either of those private methods are provided. If they are provided, the
  stream class is passed as the parameter, giving the code control over its usage.
- Encryption could be added to the output and decryption
  to the input (note that the bytes are written and read in cleartext with no
  obfuscation at all).
- , you can once again use the private methods to just throw the
  NotSerializableException.
- you can implement Externalizable,
- That means that if the state of the written
  object is written and then written again, the new state will not be saved!
- That flattened object sits in the file system for some
  time.
- because all persistent-capable
  classes are automatically given a unique identifier. If the identifier of the
  class does not equal the identifier of the flattened object, the exception will
  be thrown.
- If you wish to control versioning, you simply have to provide the serialVersionUID
  field manually and ensure it is always the same, no matter what changes you make to
  the classfile.
- serialver Baz

02 Nov 09

ClassLoader说明 - 锈材技术收藏站 - JavaEye技术网站

without code

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classloader java article example starred

大家可以看看sun.misc.Launcher的源码，Bootstrap和Extention就在该文件里。该src可以在sun的网站上下载该压缩包，约60M(jdk-1_5_0-src-scsl.zip)，它不在jdk自带的那个src.zip里。
在一个单虚拟机环境下，标识一个类有两个因素：class的全路径名、该类的ClassLoader。
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- 代理模型是Java安全模型的保证。譬如，我们自己写一个String.java，并且编译、package到自己的java.lang包下。按照代理模型，当前线程的ClassLoader会将其代理到父ClassLoader，父ClassLoader(最终会是Bootstrap)会找到 rt.jar下的String.class，也就是说我们的String.class不会捣乱。
- 将应用的ClassLoader从默认的Parent-First，改成Parent-Last就可以解决
- 1、应用框架可以自己控制Classes的目录，并且自动部署。
  
  我读过Jive公司的Wildfire(著名的即时通讯服务器)，它自己有一套应用框架，非常灵活，遵循该框架插件规范的的第三方的plug-in放置在指定目录可以自动部署，实现某些扩展功能，如文件传输、语音聊天。

Tacit Records: The Java Class Loader — Developer.com

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classloader java article

Since each class loader is itself a class, the question as to which comes first is often asked.
The SecureClassLoader is an extension of ClassLoader and a standard class loader within the JDK runtime library.
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- java.net.URLClassLoader
- sun.applet.AppletClassLoader
- java.rmi.server.RMIClassLoader
- sun.misc.Launcher$ExtClassLoader
- sun.misc.Launcher$AppClassLoader

Java 编程的动态性，第 1 部分：类和类装入 - K.Y.Z@CSDN - CSDN博客

blog.csdn.net/...35510.aspx - Preview

classloader article tomcat starred

在编写应用程序以使用接口时，可以到运行时才指定其实际实现。这个用于组装应用程序的后联编方法广泛用于 Java 平台，servlet 就是一个常见示例。
每个构造好的类在某种意义上是由装入它的类装入器所“拥有”。类装入器通常保留它们所装入类的映射，从而当再次请求某个类时，能通过名称找到该类。
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- 这里 Common 类装入器从 Tomcat 安装的某个特定目录的 JAR 文件进行装入，旨在用于在服务器和所有 Web 应用程序之间共享代码。Catalina 装入器用于装入 Tomcat 自己的类，而 Shared 装入器用于装入 Web 应用程序之间共享的类。最后，每个 Web 应用程序有自己的装入器用于其私有类。
- 在 Java 2 平台中将 setContextClassLoader 方法和 getContextClassLoader 方法添加到了 java.lang.Thread 类中。这些方法允许该框架设置类装入器，使得在运行每个应用程序中的代码时可以将类装入器用于该应用程序。
- 类装入器的灵活性甚至允许动态地重新装入已修改的代码

01 Nov 09

page 2 > The Chain of Responsibility pattern's pitfalls and improvements - JavaWorld

www.javaworld.com/...jw-0816-chain.html - Preview

pattern article best-practice servlet filter event starred

By nature, a global event hook chain is not classic CoR. The event must be delivered to all listeners in the chain,
regardless of whether a listener already handles it. So the CallNextHookEx() call seems to be the job of the base class, not the individual listeners. Letting the individual listeners make the call
doesn't do any good and introduces the possibility for stopping the chain accidentally.
"4. a) Either invoke the next entity in the chain using the FilterChain object (chain.doFilter()), 4. b) or not pass on the request/response pair to the next entity in the filter chain to block the request processing."

page 1 > The Chain of Responsibility pattern's pitfalls and improvements - JavaWorld

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pattern article best-practice servlet filter event starred

I wrote two Java programs (for Microsoft Windows OS) that must catch global keyboard events generated by other applications
concurrently running on the same desktop. Microsoft provides a way to do that by registering the programs as a global keyboard
hook listener.
The code that registers the program itself as a hook listener was missing the CallNextHookEx() call required by the hook framework.
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- Events are sent to the first listener in the chain. To allow all
  listeners to receive events, each listener must make the CallNextHookEx() call to relay the events to the listener next to it. If any listener forgets to do so, the subsequent listeners will not
  get the events; as a result, their designed functions will not work.

31 Oct 09

JOT: Journal of Object Technology - UML 2 Composition Model, Conrad Bock

www.jot.fm/...column5 - Preview

uml 2.0 composition toread article

21 Oct 09

Presentation Model

www.martinfowler.com/...PresentationModel.html - Preview

design pattern mvc article GUI

The view either stores all its
state in the Presentation Model or synchonizes its state with
Presentation Model frequently
In the case of composition a Presentation Model may contain
one or many child Presentation Model instances, but each child
control will also have only one Presentation Model.

Separated Presentation

www.martinfowler.com/...SeparatedPresentation.html - Preview

design pattern mvc article GUI

As well as a separation, there is also a strict visibility
rule. The presentation is able to call the domain but not
vice-versa. This can be checked as part of a build with dependency
checking tools.
Although the domain cannot call the presentation it's often
necessary for the domain to notify the presentation if any changes
occur. Observer is the usual solution to this
problem.
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- Ask yourself if anything would be duplicated between
  the GUI and command line presentation code - if it is then it's a
  good candidate for moving to the domain.

29 Sep 09

主流媒体不小心透露了中国人身上的四条吸血管

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economy china US stock market politics article analysis starred

Kenyth Zeng's Library tagged article → View Popular

第八组第三次作业--穿越GFW技术及其控制方法

Buffer和cache的区别是什么？ - delphij's Chaos

探索 CouchDB

InfoQ: SproutCore: An HTML 5 Application Framework

InfoQ: Virtual Panel: Evolution of JavaScript Frameworks for HTML 5

InfoQ: JavaRebel: Dynamic Classloading in the JVM

幂律分布-搜狐财经

Class Loading in Java: Time to Add Dynamicity? | Javalobby

How JavaRebel Saves Development Time | Javalobby

Understanding Network Class Loaders

Discover the secrets of the Java Serialization API

ClassLoader说明 - 锈材技术收藏站 - JavaEye技术网站

Tacit Records: The Java Class Loader — Developer.com

Java 编程的动态性，第 1 部分：类和类装入 - K.Y.Z@CSDN - CSDN博客

page 2 > The Chain of Responsibility pattern's pitfalls and improvements - JavaWorld

page 1 > The Chain of Responsibility pattern's pitfalls and improvements - JavaWorld

JOT: Journal of Object Technology - UML 2 Composition Model, Conrad Bock

Presentation Model

Separated Presentation

主流媒体不小心透露了中国人身上的四条吸血管

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