BlogJava-Jcat-随笔分类-Java

Groovy 修饰符

Jcat — Mon, 10 Nov 2008 04:30:00 GMT

Groovy把最常用的东西都设置成default了，经常可以省这省那的（比如括号、分号、public等）；又加上闭包，初学的时候，有些代码，一眼望去，都分不清是方法、是类、还是闭包。
这里先简单总结一下常用的修饰符。

package jcat.bit.g

/*
修饰符有三类：
1. static
2. 作用域：public(默认), private, protected.
3. 类型：def（默认，动态）, void（无类型，静态）, 其它常规静态类型
*/
class Test {
    static def a_static_def = 'a_static_def'
    static a_static = 'a_static'
    def a_def = 'a_def'

    static void main(strs) {
        println a_static_def
        println a_static

        println t_static_def()
        println t_static()

        new Test().with {
            println a_def

            println t_public_def()
            println t_public()
            println t_def()
        }
    }

    static def t_static_def() { // def = 可以返回任何类型，包括void
        return "t_static_def"
    }

    static t_static() { // 有其它修饰符可以省略def（默认public + def）
        return "t_static"
    }

    public def t_public_def() {
        return "t_public_def"
    }

    public t_public() { // 默认def
        return "t_public"
    }

    def t_def() { // 至少要有一个修饰符，所以这个def不能省略; 且默认public
        return "t_def"
    }

    static void t_static_void() {
        //return "t_static_void"    // cannot return an object from a method that returns "void"
    }
}

Jcat 2008-11-10 12:30 发表评论

Groovy JDBC

Jcat — Fri, 07 Nov 2008 07:02:00 GMT

用JDBC操作数据库，对比一下Java和Groovy。

环境：SQL Server 2000 （记得打补丁SP4，不然JDBC访问会报错）
JDBC Driver：msbase.jar，mssqlserver.jar，msutil.jar

Java版

package jcat.bit.java;

import java.sql. * ;

public class JDBC {
     public static void main(String[] args) throws ClassNotFoundException, SQLException {
        Class.forName( " com.microsoft.jdbc.sqlserver.SQLServerDriver " );
        Connection conn = DriverManager.getConnection(
                 " jdbc:microsoft:sqlserver://localhost:1433;DatabaseName=pubs " ,
                 " sa " , "*** " );

        Statement stmt = conn.createStatement();
        ResultSet rs = stmt.executeQuery( " select top 10 * from authors " );

         while (rs.next()) {
            System.out.println(rs.getString( 2 ) + " " + rs.getString( 3 ));  // 数id
        }

        rs.close();
        stmt.close();
        conn.close();
    }
}

Groovy版

package jcat.bit.groovy

import groovy.sql.Sql

class JDBC {
    static void main(args) {
        Sql sql = Sql.newInstance(
                "jdbc:microsoft:sqlserver://localhost:1433;DatabaseName=pubs",
                "sa", "***",
                "com.microsoft.jdbc.sqlserver.SQLServerDriver")
        sql.eachRow("select top 10 * from authors") {row ->
            println row.au_fname + " " + row.au_lname    //直接用数据库的字段名就可以操作结果集了，不用去数id
        }
    }
}

总结
1. 建立查询，差别不大，都是JDBC那一套；Groovy不用处理异常
2. 处理查询结果，Groovy因为有闭包，处理这些迭代问题很方便
3. Groovy不用关闭

Jcat 2008-11-07 15:02 发表评论

Groovy Closure “操作”也成了参数

Jcat — Thu, 06 Nov 2008 18:04:00 GMT

1. 闭包代表（定义）了一段代码（操作）：光看这一句，其实方法也能实现相同的功能呀。
2. 闭包可以作为方法的参数：这才是闭包的特殊之处和真正意义。

下面演示一个只有闭包能做，方法做不到的例子。

方法的作用是提炼共性，再代之以不同的参数。即对不同的“数据”进行相同的“操作”。从3个loop可以看出：
    Comm1：相同的数据
    Comm2：相同的for循环
    Diff1：循环体内执行的操作不同

Comm1很好搞定，参数aa就是提炼出的共性
Comm2看似是共性，却很难提炼，因为for循环和循环体内的操作实际是一个整体；Comm2被Diff1纠缠，3个loop是完全不同的3组操作，无法提炼。

比如，如果现在想要按照奇数循环，只能依次改动三个循环。

int [] aa = [ 1 , 2 , 3 , 4 , 5 , 6 ]

// loop1
for ( int i = 0 ; i < aa.length; i ++ ) {
    println aa[i]
}

// loop2
for ( int i = 0 ; i < aa.length; i ++ ) {
    print aa[i]
}

// loop3
for ( int i = 0 ; i < aa.length; i ++ ) {
    print aa[i] + ' '
}

// loop1
for ( int i = 0 ; i < aa.length; i += 2 ) {
    println aa[i]
}

// loop2
for ( int i = 0 ; i < aa.length; i += 2 ) {
    print aa[i]
}

// loop3
for ( int i = 0 ; i < aa.length; i += 2 ) {
    print aa[i] + ' '
}

下面我们看看闭包的强大之处，Comm1和Comm2都被很好的封装在了loop方法里；Diff1则作为参数（闭包）传入loop方法。

static void main(String[] a) {
    int[] aa = [1, 2, 3, 4, 5, 6]

    loop(aa) { println it }
    loop(aa) { print it }
    loop(aa) { print it + ' ' }
}

如果我们想要改变循环的方式，只需要改一处

static void loop(int[] aa, Closure c) {
    for (int i = 0; i < aa.length; i++) {
        c.call(aa[i])
    }
    println ' '
}

static void loop(int[] aa, Closure c) {
    for (int i = 0; i < aa.length; i += 2) {
        c.call(aa[i])
    }
    println ' '
}

总结，闭包本身并没什么难点，关键是怎样合理的设计一个接受Closure类型参数的方法。从GDK的方法也可以看出，大多数接受闭包的方法都是和数组迭代有关（也即循环）。

Jcat 2008-11-07 02:04 发表评论

Groovy Closure

Jcat — Thu, 06 Nov 2008 10:50:00 GMT

Definition

    /*
        1. 变量是用来装“数据”的，闭包就是用来装“操作”的
        2. 和定义一个方法一样，闭包也可以有入参
        */
        Closure p = {x ->
            print x + ' '
        }
        [ 1 , 2 , 3 ].each(p)

        [ 4 , 5 , 6 ].each({x -> // 闭包是可以匿名的
            print x + ' '
        })

        [ 7 , 8 , 9 ].each {x -> // 括号是可以省略的
            print x + ' '
        }

        [ 10 , 11 , 12 ].each { // it是默认的参数名字，所以这里连入参的定义都省了
            print it + ' '
        }

Using

package jcat.bit

class Test {
    /*
    1. 闭包是对象，是Closure类的实例，所以：
        1）可以在类里定义Closure类型的属性
        2）可以在方法里定义Closure类型的变量
        3）可以定义一个方法，接收Closure类型的参数
    2. 闭包又有方法特质，毕竟它装的是“操作”，甚至可以像调用方法一样调用闭包
     */

    static final Closure PRINT_STR = {  // 属性（类变量）
        println it
    }

    static void main(String[] a) {
        /*
        闭包类似Java的内部类，区别是闭包只有单一的方法可以调用，但可以有任意的参数，
        闭包用“{}”括起，“->”前面是参数，后面是处理语句，可以直接调用，也可以使
        用call调用。不管那种调用，最后groovy编译器都会把编译成对doCall方法的调用，
        这是groovy对闭包的一个隐藏方法。
         */
        PRINT_STR("像方法一样调用")
        PRINT_STR.call("作为Closure的实例，再调用相应的方法")

        Closure printLength = {String s ->  // 局部变量
            println s.length()
        }
        printLength("AAA")

        /*
        通常，操作是死的，我们能动态代入的是“数据”。
        闭包使得我们可以动态的代入一段“操作”。
        “闭包是可以用作方法参数的代码块。”
         */
        closureAsParameter(null, printLength)
        closureAsParameter("BBB", PRINT_STR)
    }

    static void closureAsParameter(String s, Closure c) {
        if (s != null) {
            c.call(s)
        }
    }
}

-----------------------------------------------------------------
附上一个Java的匿名内部类的例子，用来和闭包对比一下。

package jcat.bit;

public class AnonymousInnerClass {
    public static void main(String[] args) {
        AbsClass a = new AbsClass() {
            public void foo(String s) {
                System.out.println(s);
            }
        };

        a.foo("ABC");

        AbsClass b = new AbsClass() {
            public void foo(String s) {
                System.out.println(s.length());
            }
        };
        b.foo("ABC");
    }
}

abstract class AbsClass {
    public abstract void foo(String s);
}

Jcat 2008-11-06 18:50 发表评论

Hello Grails

Jcat — Tue, 04 Nov 2008 14:04:00 GMT

最近BI的项目不忙，抽空怀念了一下编程技术：

1. 同事给了我份Flex的教程，把前三章看了一下，有了初步的了解；FlexBuilder也用了一把，不错，效果很绚丽。

2. 恰逢IDEA 8 EAP (Early Access Preview)发布，搞了一个装上试试。主要试了试对Flex的支持，感觉还有待提升。另外IDEA对内存的消耗似乎越来越多了，没做深入体验。

3. 拿出了小二去年送我的生日礼物《Grails权威指南》，翻了翻，Hello World一会就做好了。打算再进一步体验一下。

Jcat 2008-11-04 22:04 发表评论

java foundation

Jcat — Wed, 23 May 2007 14:35:00 GMT

---String---

equals in String

public boolean equals(Object anObject) {
    if (this == anObject) {
        return true;
    }
    if (anObject instanceof String) {
        String anotherString = (String)anObject;
        int n = count;
        if (n == anotherString.count) {
        char v1[] = value;
        char v2[] = anotherString.value;
        int i = offset;
        int j = anotherString.offset;
        while (n-- != 0) {
            if (v1[i++] != v2[j++])
            return false;
        }
        return true;
        }
    }
    return false;
    }

equals in Object

   public boolean equals(Object obj) {
    return (this == obj);
    }

    System.out.println(new String("aa").equals(new String("aa"))); //true
    System.out.println(new String("aa") == new String("aa"));      //false
    System.out.println("aa".equals("aa"));                         //true
    System.out.println("aa" == "aa");                              //true

Jcat 2007-05-23 22:35 发表评论

environment variable for java, groovy, ant and etc.

Jcat — Wed, 23 May 2007 13:39:00 GMT

JAVA_HOME

ANT_HOME

CATALINA_HOME

GROOVY_HOME

GRAILS_HOME

classpath=.
(%JAVA_HOME%\jre\lib is not required)

Path=%JAVA_HOME%\bin;%ANT_HOME%\bin;%CATALINA_HOME%\bin;%GROOVY_HOME%\bin;%GRAILS_HOME%\bin

Note: if you add %GROOVY_HOME%\embeddable\groovy-all-1.0.jar to classpath Grails can't work correctly.

Jcat 2007-05-23 21:39 发表评论

Struts

Jcat — Sun, 08 Apr 2007 15:47:00 GMT

struts用了也一年了，基本的东西都会用，不过因为是在工作中边学边用，难免很多知识点都不系统，惭愧呀。这几天找本书梳理一下。

---MVC---
V：多种视图共享一个后台模型
M：实现与界面独立，良好的封装
C：更好的维护程序流程

model1：JSP（V、C）+JavaBean（M）
只适用于小型程序，JSP的双重角色使HTML和Java混合，很难维护。

model2：JSP(V)+Servlet(C)+JavaBean(M)
Struts也是model2（用ActionServlet代替Servlet）。Struts的所有功能都是建立在已有的Java Web组件上，如Servlet，JSP，JavaBean，它只是利用一种方式将这些元素组织了起来，使它们协同工作。

---点滴---
在Struts应用程序中，所有的用户请求都由ActionServlet接收，然后根据struts-config.xml查找相应的子控制器。Web容器加载Struts应用程序后，struts-config.xml被首先读入内存成为一个ActionMapping对象。

基本流程：HttpRequest-->XxxForm-->validate()=true-->XxxAction-->execute()-->(return) ActionForward-->JSP
这其中的配置信息都存在于struts-config中

国际化： + ApplicationResources.properties

---web.xml---

ApplicationContext name
配置事件监听器

--> Session过期时间

根URL的默认页面：先找index文件，找不到再查找该list

制定在返回特定HTTP状态码，或者特定类型的异常被抛出时显示的页面。
对标记库描述符文件（Tag Library Descriptor File）指定别名

---struts-config.xml---

定义数据源

定义全局异常

定义全局转发（名字相同时，局部转发优先）
定义控制配置类，如TilesRequestProcessor

指定消息资源文件，配合使用

插件

---Action们---
Action：线程安全的，所以都是singlon的。不应该在Action类中使用域变量保存用户特定信息，如状态信息（可以将一些与特定请求无关的变量定义为域变量，如Log变量）
ActionForward：可以是静态的从config文件中读，如mapping.findForward("success")；也可以是动态的指定，如new ActionForward("success","/aaa/bbb.jsp",true)

预定义的Action
ForwardAction：类似
IncludeAction：类似
以上两个Action，使Struts遵循MVC，避免直接调用JSP，可以充分利用控制器的预处理功能。
DispatchAction：以资源为中心，减少Action的数量。
通常可设置parameter="method"，则调用的url为http://xxx/yyy?method=add
也可以设置parameter="add, update"，则调用的url为http://xxx/yyy?add=true
LookupDispatchAction：DispatchAction的子类，通过反查资源绑定，找到类中对应的方法。
SwitchAction：Struts支持多应用程序模块（即multi-module），SwitchAction用来执行在不同应用程序模块间的切换操作。

Jcat 2007-04-08 23:47 发表评论

Apache vs Tomcat

Jcat — Tue, 06 Mar 2007 13:00:00 GMT

本质区别：
1）
apache支持静态页面；
tomcat支持动态页面，比如servlet等。
2）
apache是web（http）服务器，它是专门用于提供HTTP服务，以及相关配置的（例如虚拟主机、URL转发等等）
tomcat是应用（java）服务器，它只是一个servlet（jsp）容器，可以认为是apache的扩展，但是可以独立于apache运行。
3）
apache是一辆卡车，上面可以装一些东西如html等。但是不能装水，要装水必须要有容器（桶），而这个桶也可以不放在卡车上。

使用区别：
tomcat 作为 jsp，servlet 容器，虽然有静态解析功能，但性能上与 apache 相比相差很远。
apache 可以运行一年不重启，稳定性非常好，而 tomcat 则不见得。

整合：
一般使用apache+tomcat的话，apache只是作为一个转发，对jsp的处理是由tomcat来处理的。

整合的好处是：
如果客户端请求的是静态页面，则只需要Apache服务器响应请求，apache 解析 html 等静态网页非常快，是经过无数测试证明的。
如果客户端请求动态页面，则是Tomcat服务器响应请求。
因为jsp是服务器端解释代码的，这样整合就可以减少Tomcat的服务开销。

其它：
Tomcat是Apache组织在符合J2EE的JSP、Servlet标准下开发的一个JSP服务器

some official definitions:
What is the Apache HTTP Server?
    * is a powerful, flexible, HTTP/1.1 compliant web server
    * implements the latest protocols, including HTTP/1.1 (RFC2616)
    * is highly configurable and extensible with third-party modules
    * can be customised by writing 'modules' using the Apache module API
    * provides full source code and comes with an unrestrictive license
    * runs on Windows 2003/XP/2000/NT/9x, Netware 5.x and above, OS/2, and most versions of Unix, as well as several other operating systems

What is the Apache Tomcat?
    Apache Tomcat is the servlet container that is used in the official Reference Implementation for the Java Servlet and JavaServer Pages technologies. The Java Servlet and JavaServer Pages specifications are developed by Sun under the Java Community Process.
    Apache Tomcat is developed in an open and participatory environment and released under the Apache Software License.

Jcat 2007-03-06 21:00 发表评论

input data from cmd

Jcat — Sun, 04 Feb 2007 11:24:00 GMT

import java.io.InputStreamReader;
import java.io.BufferedReader;
import java.io.IOException;

/**
* User: Jcat
* Date: 2006-11-19
*/
public class Lab {
     public static void main(String[] args) throws IOException {
        InputStreamReader ir;
        BufferedReader in;
        String s;

        ir = new InputStreamReader(System.in);
        in = new BufferedReader(ir);
        s = in.readLine();
        System.out.println(s);
    }
}

Jcat 2007-02-04 19:24 发表评论

The ultimate webdesign usability checklist

Jcat — Thu, 25 Jan 2007 04:39:00 GMT

I noticed that I, and fellow webdesigners, keep making the same usability mistakes over and over. This checklist with 88 questions is a must read for every webdesigner who cares about usability.

This website, NotUsable.com, is not designed by me. Giving me the perfect excuse why this website doesn’t pass my own usability checklist. But I would love to hear your comments and don’t forget to let me know when you can answer the whole checklist with ‘yes’!

Note that my design company is called Achtentachtig, which means Eighty Eight in Dutch, that’s why there are 88 questions in this checklist. Just to let you know.

Enough talking, let’s start!

Technical

Did you validate your (X)HTML using W3C Markup Validation Service?
Did you validate your CSS using W3C CSS Validation Service?
Did you check your website in at least IE, FF, Opera and Safari?

Images

Did you add the ALT and TITLE attributes to all your important images?
Did you add the LONGDESC attributes to all your image that need a description?
Did you write effective ALT text?
Did you make the size of your pages less then 50KB?
Did you choose the appropriate filetype for your images?
Did you add a description to images that support your content?
Did you use plain text instead of images for important content?

Content

Did you use a sans-serif typeface with a decent font size for your body text?
Did you adjusted the leading and tracking, if necessary, to increase readability?
Did you align your body text to the left? (depends on language)
Did you use EM or percentages instead of PX?
Did you make sure that there are no whole sentences in uppercase?
Did you use less then 78 characters, including spaces, per line?
Did you make brief and precise paragraphs with explanatory titles?
Did you use lists to sum things up?
Did you write your conclusion first and then your explanation?
Did you create enough contrast between the text and the background?
Did you make your website also accessible for text-only browsers?
Did you make sure that there are no ‘under construction’ pages?
Did you include a print function on pages with a large amount of text?
Did you include a print stylesheet?
Did you replace all special characters with the ISO Latin-1 codes?
Did you spell check your content and did you proofread for grammar errors??

Navigation

Did you make sure that all your links work? W3C Link checker does the job.
Did you include a link to all your main pages on your homepage?
Did you include your main navigation on every page?
Did you use no more then 8 items in your main navigation?
Did you distinguish the active and nonactive page in the menu?
Did you use self explanatory link text instead of ‘click here’?
Did you use self explanatory link text instead of business terms?
Did you make a distinction between visited and non-visited links?
Did you make a distinction between links and plain text?
Did you add the TITLE attribute to all your links?
Did you use breadcrumbs if you have a large amount of pages?
Did you include a search option if you have a large amount of pages?
Did you make your logo link to your homepage?
Did you make a skip to content link at the top of your pages?
Did you make a skip to menu link at the top of your pages?
Did you make it possible to browse your website using SHIFT-TAB and RETURN?
Did you make sure you didn’t use any javascript links?

Structure

Did you make a consistent page structure?
Did you place your logo at the top left?
Did you place an explanatory tag line next to your logo?
Did you place your search box at the top right?
Did you place important content above the fold/scroll?
Did you make your design on a grid system?
Did you make your design fluid using percentages?
Did you make your website also viewable on low resolutions?
Did you make custom titles (as in TITLE tag) for all your pages?

Forms

Did you make sure that users don’t return to an altered form after an error?
Did you make a friendly and informative error page?
Did you make a friendly ‘thank you’ page with a confirmation email?
Did you add only a ’submit’ button and no ‘reset’ button?
Did you tell the user what to expect after clicking the submit button?
Did you split long forms up into multiply pages?
Did you gave the user room to type?
Did you place an asterisk when a field is compulsatory?
Did you keep the standard look of input fields that is generated by the browser?
Did you create a logical order of asking information?
Did you use double input fields for passwords only?
Did you let the computer, not the user, handle information formatting?
Did you make sure that users can fill in the entire form using the TAB key?
Did you explain to the user why you ask certain information?
Did you explain to the user what you are going to do with that information?
Did you use realtime validation using AJAX?
Did you use the LABEL tag?
Did you place the LABEL above the input field, instead of next to it?
Did you choose the correct input type for different data?
Did you make the top input field automatically active using setfocus?
Did you destinguish the active field from non-active fields using input:focus?
Did you use the FIELDSET and LEGEND entities when appropriate?
Did you check if your forms also work with Javascript turned off?

Multimedia

Did you make sure that essential information/navigation is not made in Flash?
Did you make sure that music and videoclips don’t start playing automatically?
Did you make sure that music and videoclips can be turned off at any time?
Did you inform the user about the size and length of your music and videoclips?

Extra features

Did you make a custom 404 page?
Did you make a site map?
Did you make a rss feed? (if you add content regularly)
Did you make a high contrast version of your website?
Did you make good looking URL’s (like this one)?
Did you make sure that there are no frames on your website?
Did you make sure that there are no pop ups on your website?
Did you make a contact form instead of just an email link?

Any suggestions?

Add number 88 by giving a comment on this post!

原文地址

Jcat 2007-01-25 12:39 发表评论

online status indicator

Jcat — Wed, 20 Dec 2006 01:34:00 GMT

QQ

yahoo.cn

yahoo

onlinestatus.msn

关于msn，似乎还没有找到官方的服务（垃圾微软），第三方提供的服务总是不太稳定

Jcat 2006-12-20 09:34 发表评论

一些页面自动跳转的实现

Jcat — Wed, 22 Nov 2006 09:20:00 GMT

功能：5秒后，自动跳转到同目录下的02view.html文件

1）html的实现

优点：简单
缺点：Struts Tiles中无法使用

2）javascript的实现

优点：灵活，可以结合更多的其他功能
缺点：受到不同浏览器的影响

3）结合了倒数的javascript实现（IE）

<span id="totalSecond">5span>

<script language="javascript" type="text/javascript">
var second = totalSecond.innerText;
setInterval("redirect()", 1000);
function redirect(){
totalSecond.innerText=--second;
if(second<0) location.href='02view.html';
}
script>

优点：更人性化
缺点：firefox不支持（firefox不支持span、div等的innerText属性）

3'）结合了倒数的javascript实现（firefox）

4）解决Firefox不支持innerText的问题

<span id="totalSecond">5span>

<script language="javascript" type="text/javascript">
if(navigator.appName.indexOf("Explorer") > -1){
document.getElementById('totalSecond').innerText = "my text innerText";
} else{
document.getElementById('totalSecond').textContent = "my text textContent";
}
script>

5）整合3）和3'）

<span id="totalSecond">5span>

<script language="javascript" type="text/javascript">
    var second = document.getElementById('totalSecond').textContent;

    if (navigator.appName.indexOf("Explorer") > -1)
    {
        second = document.getElementById('totalSecond').innerText;
    } else
    {
        second = document.getElementById('totalSecond').textContent;
    }

    setInterval("redirect()", 1000);
    function redirect()
    {
        if (second < 0)
        {
            location.href = '02view.html';
        } else
        {
            if (navigator.appName.indexOf("Explorer") > -1)
            {
                document.getElementById('totalSecond').innerText = second--;
            } else
            {
                document.getElementById('totalSecond').textContent = second--;
            }
        }
    }
script>

Jcat 2006-11-22 17:20 发表评论

TAKE ALL'S FISH

Jcat — Sat, 12 Aug 2006 07:28:00 GMT

吉祥三宝

http://struts.apache.org/

http://www.springframework.org/

http://www.hibernate.org/

Apache

http://ant.apache.org/
Apache Ant is a Java-based build tool. In theory, it is kind of like Make, but without Make's wrinkles.

http://lucene.apache.org/
Apache Lucene is a high-performance, full-featured text search engine library written entirely in Java. It is a technology suitable for nearly any application that requires full-text search, especially cross-platform.

http://jakarta.apache.org/commons/index.html
The Commons is a Jakarta subproject focused on all aspects of reusable Java components.

http://jakarta.apache.org/velocity/index.html
Velocity is a Java-based template engine. It permits anyone to use a simple yet powerful template language to reference objects defined in Java code.

Sourceforge

http://junit.sourceforge.net/
JUnit is a simple framework to write repeatable tests. It is an instance of the xUnit architecture for unit testing frameworks.

http://httpunit.sourceforge.net/
HttpUnit makes you easy to be able to bypass the browser and access your site from a program. When combined with a framework such as JUnit, it is fairly easy to write tests that very quickly verify the functioning of a web site.

http://dozer.sourceforge.net/
Dozer is a powerful, yet simple Java Bean to Java Bean mapper that recursively copies data from one object to another. Typically, these Java Beans will be of different complex types.

http://xdoclet.sourceforge.net/xdoclet/index.html
XDoclet is an open source code generation engine. It enables Attribute-Oriented Programming for java. In short, this means that you can add more significance to your code by adding meta data (attributes) to your java sources. This is done in special JavaDoc tags.

http://displaytag.sourceforge.net
The display tag library is an open source suite of custom tags that provide high-level web presentation patterns which will work in an MVC model. Actually the display tag library can just... display tables! Give it a list of objects and it will handle column display, sorting, paging, cropping, grouping, exporting, smart linking and decoration of a table in a customizable XHTML style.

http://cglib.sourceforge.net/
cglib is a powerful, high performance and quality Code Generation Library, It is used to extend JAVA classes and implements interfaces at runtime.

Others

http://www.opensymphony.com/compass/
Compass is a first class open source Java Search Engine Framework, enabling the power of Search Engine semantics to your application stack decoratively. Built on top of the amazing Lucene Search Engine, Compass integrates seamlessly to popular development frameworks like Hibernate and Spring.

http://www.opensymphony.com/quartz/
Quartz is a full-featured, open source job scheduling system that can be integrated with, or used along side virtually any J2EE or J2SE application - from the smallest stand-alone application to the largest e-commerce system.

http://groovy.codehaus.org/
Groovy is an agile dynamic language for the Java Platform with many features that are inspired by languages like Python, Ruby and Smalltalk, making them available to Java developers using a Java-like syntax.

http://www.singularsys.com/jep/
JEP is a Java library for parsing and evaluating mathematical expressions. With this package you can allow your users to enter an arbitrary formula as a string, and instantly evaluate it. JEP supports user defined variables, constants, and functions. A number of common mathematical functions and constants are included.

http://www.dom4j.org/
dom4j is an easy to use, open source library for working with XML, XPath and XSLT on the Java platform using the Java Collections Framework and with full support for DOM, SAX and JAXP.

http://www.castor.org/
Castor is an Open Source data binding framework for Java. It's the shortest path between Java objects, XML documents and relational tables. Castor provides Java-to-XML binding, Java-to-SQL persistence, and more.

Jcat 2006-08-12 15:28 发表评论

Hello Velocity

Jcat — Tue, 08 Aug 2006 00:21:00 GMT

单行注释： ##your note
多行注释： #*your note*#

不能直接访问对象的域，只能通过方法来访问。关于方法的调用，有两种变体（Velocity会帮你调用相应的方法）：
1）对于context中的Hashtable对象，可以直接用$hashtable.key来得到value，相当于$hashtable.get(key)
2）对于context中的JavaBean对象，可以直接用$javaBean.property来访问，相当于$javaBean.getProperty()

安静引用符（Quiet Reference Notation）$!
作用：当引用的变量为null时，将输出空字符串。（如果用$xxx，当null时，会输出字符串"$xxx"）

双引号中的$xxx将仍然被解析；单引号中的$xxx将不被解析，输出字符串"$xxx"

关于路径：
1. 为VelocityEngine指定velocityLoaderPath，该路径为存放vm文件的根目录（其下可以建子文件夹，无需另外指定）
2. 对vm的引用都是以velocityLoaderPath开始的绝对路径。比如：

|-velocityLoaderPath
   |-a.vm
   |-B
     |-b.vm

在b.vm中引用a.vm：#parse("a.vm") 正确； #parse("../a.vm") 错误

Jcat 2006-08-08 08:21 发表评论

Doohickey

Jcat — Sat, 05 Aug 2006 16:27:00 GMT

最后的逗号
String[] strs = {"1", "2", "3", };
System.out.println(strs.length); //3

这竟然是符合语法的！

ArrayInitializer:
{ [VariableInitializer {, VariableInitializer} [,]] }
VariableInitializer: ArrayInitializer Expression
http://java.sun.com/docs/books/jls/third_edition/html/syntax.html#18.1

"This is good for quick testing. I always use this. In my case, I have a table, sometimes I care some columns, other times I care some other columns, so I am lazy to remove the last comma when I change columns. It's convenient."

运行没有main的java类
通常我们需要在java类中添加main函数才能在命令行运行这个类，但是有一种（可以让你晕死的）方法可以让你在没有main的情况下也可以运行java class（当然不是用applet），代码如下：

public class NoMainMethod
{
     static
{
        System.out.println( " Hello word, no main method! " );
        System.exit( 0 );
    }
}

static语句块会在加载类的时候加载，它在main函数之前运行。当static语句块运行完毕后，会寻找main函数，如果没有找到，就会抛出异常。但是在以上的代码中，static语句块执行后，我们终止程序的运行，所以异常就不会被抛出啦。

跳出JavaBean的命名规范
通常，JavaBean的命名规范为：属性名的第二个字母也不能大写。即不可以出现类似 aAndB 这样的属性名。如，Hibernate的PO如果出现这样的名字，将抛出net.sf.hibernate.PropertyNotFoundException异常。但是有一个办法可以解决该问题：

java file:
private String aAndB;
public String getAAndB() {
         return aAndB;
}
public void setAAndB(String aAndB) {
         this .aAndB = aAndB;
}

mapping.xml < property name ="AAndB" column ="a_and_b" />

      结研究发现，上述办法可以成功的将aAndB这样的属性与数据库mapping起来。
      显然hibernate是通过setter和getter来访问对象的属性的，所以我们可以说：mapping.xml并不是在类的属性和数据库的字段名之间做映射，而是在setter/getter和数据库的字段之间做映射。
      诚然，即使可以也别这么干，实际工作中，还是规避这种问题的好。

Jcat 2006-08-06 00:27 发表评论

Read source code is a good way to learn anything!

Jcat — Thu, 03 Aug 2006 10:43:00 GMT

Experience
To know how dose List.remove(Object) work, I do many test sample. But I still feel not very realizing. Finally, I took a look at souce code, and then I knew everything!

public boolean remove(Object o) {
    if (o == null) {
            for (int index = 0; index < size; index++)
        if (elementData[index] == null) {
            fastRemove(index);
            return true;
        }
    } else {
        for (int index = 0; index < size; index++)
        if (o.equals(elementData[index])) {
            fastRemove(index);
            return true;
        }
        }
    return false;
    }

1. List store very object's reference but object's own.
2. remove(Object) will remove the first reference in List which refer to the object
3. If you want to change an object to a new index: back up it--> remove it--> re-add it

Experience
I create a class to handle something annotated by Annotations. But it doesn't work. I found out it is returned false by Class.getMethod().isAnnotationPresent(Todo.class). Finally, I got the reason by reading source code.

public enum RetentionPolicy {
    /**
     * Annotations are to be discarded by the compiler.
     */
    SOURCE,

    /**
     * Annotations are to be recorded in the class file by the compiler
     * but need not be retained by the VM at run time.  This is the default
     * behavior.
     */
    CLASS,

    /**
     * Annotations are to be recorded in the class file by the compiler and
     * retained by the VM at run time, so they may be read reflectively.
     *
     * @see java.lang.reflect.AnnotatedElement
     */
    RUNTIME
}

Jcat 2006-08-03 18:43 发表评论

小错不断，大错不犯

Jcat — Tue, 25 Jul 2006 05:11:00 GMT

症状：刚配置好struts，可是DispatchAction怎么都不工作（Action可以工作），也不报错
原因：只引入了struts自身的jar，看一看release中lib下，还有不少非struts的jar，可以猜想这些都是DispatchAction所需要的，而Action不需要（以前以为这些没用）。不报错让我很郁闷。

症状：刚配置好struts，action可以工作了，就是不能正确的forward到jsp页面，execute中加断点，也不进入。
原因：execute有两个！！！HttpServletRequest vs ServletRequest，前者才是struts所使用的execute。

症状：在web.xml里面设置好了

<error-page>
<error-code>404error-code>
<location>/404.jsplocation>
error-page>

但当出现404错误时，并没有显示404.jsp这一页，而是显示browser提供的error report page

原因：在客户端浏览器如IE的internet选项高级属性中默认使用“友好的http错误信息”，这样会造成你的服务器是输出你所定义的错误页面，但到客户端被IE这混蛋给覆盖掉了。解决方案是你定义的错误页面的大小必须大于512bytes，就不会被客户端设置所影响了。

症状：用hibernate访问数据库，可以insert，可以select，可以drop，就是不能update，而且没有任何错误消息

原因：
设置成true即可。
（当mutable＝false，却又执行update操作时，hibernate至少应该提供警告消息告知一下才对,可惜没有，所以很难发现）

症状：
      Javascript弹出窗口时，如果用的是相对路径，形如javascript:void(window.open('../../test.html'))，不同的浏览器的处理不同（因为js是浏览器处理的东西）。
      比如，不是部署在根目录下时（根目录下又建了一个目录）：在Firefox下，是以服务器为视角，则../../即可；而在IE下，则是以浏览器为视角，则需要多加一级，如../../../。

解决：用绝对路径 javascript:void(window.open('http://www.verican.com/test.html'))；或者，用 target="_blank" href="../../test.html"> （因为这是服务器处理的东西，所以不管部署在哪里，相对路径都是唯一确定的）

症状：
刷新的时候 1）抛出ServletException
                     2）The page cannot be refreshed without resending the information, Click Retry to send the information again.

原因：Struts中redirect设置问题（具体原理以后再研究）

解决：一般的，forward到一个具体的page，redirect＝false；forward到另一个action，redirect＝true

症状：

save a form --> forward to list page --> refresh --> retry --> save the form again (error)

原因：

解决：一般的，从save一个表单后，应该forward到另一个action，且redirect＝true（而不是另一个page，即便当前action里有这个page）。这样可以保证不会通过刷新重复save数据。

症状：
      用Spring + Velocity发email，开始都好好的，也能现实图片，但当加入某一幅图片以后，无法正常显示（得到一个页面为空白的Email，虽然也有大小）。把图片从bmp换到jpg，再换到gif，未果。减小图片的尺寸、大小，未果。几乎都要绝望了～～～

原因：NOTE: Invoke addInline after setText; else, mail readers might not be able to resolve inline references correctly.（这是Spring API里的原话，NND）

感受：
      1.以前没写过发Email的程序，工作中用到了，照猫画虎拿过来就用，也没有仔细阅读文档，导致这次惨痛的教训。
      2.Spring中这部分设计的也有问题，它在两个表面上没什么关系的方法之间，建立了顺序上的依赖关系。这使得出现这种情况时，没有任何线索。

症状：
遍历List时，一调用remove就出错，（错误的）代码如下

for (Object o : list)
    {
            list.remove(o);
        }

原因：ConcurrentModificationException，有remove操作时，不能用foreach循环

解决：用传统循环（看了传统还是很有用的）

for (int i = 0; i < list.size(); i++)
    {
            list.remove(i--);
        }

注意remove过后需要 i-- (--i is wrong)

症状：

boolean b = new Integer(3) == new Integer(3); //false

原因：其实是很简单的问题，但是IDEA只会对String的 = = 做智能提示，注意即可。

症状：
org.hibernate.MappingException: Could not read mappings from resource: jcat/learn/mapping.xml

开始以为路径没写对，试验了N中路径的写发后，还是不行。后来才发现是因为mapping.xml是空的。

解决：给mapping.xml加上一个空壳就可以了（好歹空壳不等于空）

xml version="1.0" encoding="gb2312"?>
DOCTYPE hibernate-mapping SYSTEM "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd" >

<hibernate-mapping default-lazy="false">

hibernate-mapping>

NOTE：几种路径的写法
1. classpath:packagename/filename
例子：在applicationContext.xml中注册hibernate.cfg.xml

<bean id="GlobalHibernateSessionFactory" class="org.springframework.orm.hibernate3.LocalSessionFactoryBean">
        <property name="dataSource">
            <ref local="GlobalDataSource"/>
        property>
        <property name="configLocation">
            <value>classpath:hibernate.cfg.xmlvalue>
        property>
bean>

2. packagename/filename
例子：在hibernate.cfg.xml中注册mapping.xml

症状：提交表单程序，加入了上传文件的功能后，出现异常
java.lang.IllegalArgumentException: Cannot invoke com.verican.newsadmin.form.TicketForm.setUploadFile - argument type mismatch

解决：将表单声明为mulptipart类型

<html:form action="/ticket" enctype="multipart/form-data">
<html:file property="uploadFile"/>
html:form>

症状：IE cannot open the Internet site file: ....

<html>
<head>
    <title>title>
head>
<body>
    <span id="TypeDes2"/>
    <script type="text/javascript">
       TypeDes2.innerHTML = "Test Span";
    script>
body>
html>

解决：对于单标签，浏览器找不到innerHTML属性。改为双标签即可。

Jcat 2006-07-25 13:11 发表评论

Hello Hibernate

Jcat — Mon, 03 Jul 2006 06:24:00 GMT

POJO principle

1. The class can not be final

2. Must implement Serializable

3. Must contain a non-argument constructor

4. The getter and setter must be public

Jcat 2006-07-03 14:24 发表评论

Keymap in IntelliJ

Jcat — Mon, 26 Jun 2006 13:26:00 GMT

摘要: Editing Ctrl + Space Basic code completion (the name of any class, method or v... 阅读全文

Jcat 2006-06-26 21:26 发表评论

Some useful IntelliJ Plugin

Jcat — Sat, 24 Jun 2006 05:01:00 GMT

==must be installed==

RegexPlugin
http://www.intellij.org/twiki/bin/view/Main/RegexPlugin

unitTest: better (and also bigger) than JunitGenerator

CVS bar: VCS bar is too old

SpellCheckPlugin
http://www.intellij.org/twiki/bin/view/Main/SpellCheck

DBHelper: more powerful than SQL Query Plugin. Maybe the latter will be removed after I am familiar with DBHelper.
http://ca.geocities.com/davidhuo2003/dbhelper.html

Rearranger: use it in canonical class, such as bean
http://www.intellij.org/twiki/bin/view/Main/RearrangerPlugin

simpleUML
http://www.intellij.org/twiki/bin/view/Main/SimpleUML

Key promoter: Shows to user how easy he can make same action using only keyboard

==good for using==

IdeaMouseGestures: IdeaMouseGestures plugin provides easy way to assign Idea's menu items to mouse gestures.
http://www.smardec.com/products/idea.html

KonaWorks PowerPack: A new code action to easily insert an expression inside a string literal
http://www.konaworks.org/

DragNDrop: This plugin will allow a user to drag and drop files into the main pane of IntelliJ

Workspaces
http://www.intellij.org/twiki/bin/view/Main/WorkspacesPlugin

RemoteTail: The plugin allows the user to view the content of a file which could be on a different computer.

Jump to Usage: Simple plugin to make navigation to element usages easier than using Alt+F7.
http://sourceforge.net/projects/jumptousage

Library Finder: helps to find library files (.jar/.zip) for a "fully qualified" class/resource name.
http://code.google.com/p/libraryfinder/

IntelliLang: IntelliLang is a combination of three basic kinds of functionality that are meant to support the developer in dealing with certain tasks that relate to (custom) languages in IntelliJ IDEA.
http://www.jetbrains.net/confluence/display/CONTEST/IntelliLang

XPathView + XSLT-Support: required by IntelliLang
http://www.intellij.org/twiki/bin/view/Main/XPathViewPlugin

Tabifier: The tabifier plugin retabs Java code so that syntactic elements are aligned vertically.
http://www.intellij.org/twiki/bin/view/Main/TabifierPlugin

Struts Assistant: it will conflict with Struts Plugin, so Struts Assistant is enough.
http://www.intellij.org/twiki/bin/view/Main/StrutsAssistant

IdeaSpring: Helpful to edit applicationContext.xml. But it is even a commercial one! So it has to be re-download every 15 days.

XFile: defaul Changes is good enough, so maybe it will be removed later.
http://www.echologic.com/plugins/xfiles.html

UpperLowerCapitalize: just use the capticalize, since there is default upper/lower in IDEA
http://www.intellij.org/twiki/bin/view/Main/UpperLowerCapitalize

IdeaJad: a popular decompiler
http://www.tagtraum.com/ideajad.html

SyncEdit: Remove the default shortcut "Tab" (for "Next SyncEditable Word"), since I need "Tab" work normally.

World of Java
http://www.worldofjava.org/

Scratch Pad: Additional editor tool window to hold pieces of code temporarily. No syntax colouring, intentions or error highlighting.
http://www.intellij.org/twiki/bin/view/Main/ScratchPadPlugin

HTML Preview: Provides preview for html files using Mozilla browser

==learning==

TabSwitch: Open files/tabs switcher

CVS Report for IntelliJ IDEA: CVS Report for IntelliJ IDEA is a free open source plugin for IntelliJ IDEA to generate statistical reports from your CVS repository.
http://vcsreport.sourceforge.net/

RssPlugin: RSS Plugin for viewing RSS feeds within IntelliJ.
http://www.intellij.org/twiki/bin/view/Main/RssPlugin

Hibernate Tools: better than hibero which is even a commercial one!

Smart Introduce: how to use it?
http://www.intellij.org/twiki/bin/view/Main/SmartIntroducePlugin

GroovyJ: hoping it can become more powerful
http://groovy.codehaus.org/IntelliJ+IDEA+Plugin

==not very useful, so can be ignore==

Code Outline: Have not found anything useful (dosen't work in IDEA 6.0)

OpenContainingForder: Plugin for Viewing folders with Windows Explorer, but cannot open a folder. So "Alt+Shift+E" is better

LineMover: default "Ctrl+Shift+Up/Down" is enough.

SQL Query Plugin: DBHelper is good enough

SQL script editor: DBHelper is good enough

JavaDoc Browser: the window can't be big enough, so acutal browser (such as fire fox) is better.

BTW: if you have any good recommendation, welcome to share with us.

Jcat 2006-06-24 13:01 发表评论

Hello Tomcat

Jcat — Fri, 23 Jun 2006 01:11:00 GMT

1. Tomcat config file, where you can change Tomcat's port number: /conf/server.xml

< Host ... >
       ...
        < Context   path ="/app1"   docBase ="app1"   debug ="0"   reloadable ="true" />
        < Context   path ="/app2"   docBase ="app2"   debug ="0"   reloadable ="true" />
        < Context   path ="root url"   docBase ="root dir (or the path of .war)"   debug ="0"   reloadable ="note1" >
< / Host >

note1: whether auto-reload the web application, when .class file is changed
1) during developing, set reloadable=true
2) after deployment, set reloadable=false

2. Some libs

/server/lib	just for Tomcat
/shared/lib	for all web apps
/common/lib	both Tomcat and all web apps
/webapps/jcat/WEB-INF/lib	just present web app

3. Immobile Directory Structure (the names are also immobile, include uppercase/lowercase)
   /jcat
   /jcat/WEB-INF
   /jcat/WEB-INF/web.xml
   /jcat/WEB-INF/classes
   /jcat/WEB-INF/lib

Note: WEB-INF/classes is loaded by tomcat before WEB-INF/lib , so classes has priority than lib

4. Scopes
      Application：在整个web应用程序内有效。对应于servelet中的ServletContext对象，Action中的获取：getServlet().getServletContext()
      Session：在一个用户与服务器建立连接的整个过程中有效。Action中的获取：httpServletRequest.getSession()
      Request：在一个请求周期内有效。就是从你点击页面上的一个按钮开始到服务器返回响应页面为止（包括响应页面）。
      Page：仅在一个jsp页面内有效。

*1* Request in Struts: PageFrom (request.setAttribute by using Form)-->Action(request.getAttribute&setAttribute)-->PageTo (request.getAttribute by using EL)

*2* : Parameter vs Attribute in request
   Parameter 是 URL 带过来的参数，只能是个 String ，如 www.verican.com/test?para1=1¶2=ttt
   在 Action 中的调用： request.getParameter("para1");
   在响应页面中的调用： ${param.para1} （ param 是 EL 的隐藏对象）

   Attribute 一般是 Form 带过来的属性，可以是任何对象
    在 Action 中的调用：一般已经存在于 Form 对象中;
   在响应页面中的调用： ${attributeName.xxx} （ EL 会自动调用 getXxx 方法，所以该 attribute 必须实现 getXxx 方法）

5. Web server跟踪客户状态的四种方法（HTTP是无状态的协议）
    1）建立含有跟踪数据的隐藏表格字段
    2）重写包含额外参数的URL
    3）使用持续的Cookie
    4）使用Servlet API中的Session机制

6. JavaBean的标准
   1) should be a public class
   2) should have a non-argument constructor
   3) fields should be privated, and using get & set to access them
   4) also can have some other functions as a common class

Jcat 2006-06-23 09:11 发表评论

How to use jar to implement double-click-run like .exe file

Jcat — Mon, 19 Jun 2006 14:45:00 GMT

1. workdir=learnJar

目录结构
+ learnJar
| mf.mf
|+ test
| Test.java

2. workdir>javac test\Test.java

+ learnJar
| mf.mf
|+ test
| Test.java
| Test.class

3. workdir>jar cvfm a.jar mf.mf test\Test.class

NOTE
1. manifest.mf可以放在任何位置，也可以是其它的文件名(反正最后jar中的文件名会被自动变为MANIFEST.MF)
2. "Manifest-Version: 1.0"--该行(以及其它行)冒号后面必须是个空格，否则jar时出错"invalid header field"
3. "Main-Class: test.Test<回车>"--该行必须以一个回车符结束，否则无效。
4. 如果是有UI的程序，双击jar文件即可运行。(如果安装了winrar等压缩软件，jar文件会被关联，因此，双击时并不会执行jar程序，而是调用压缩软件来打开jar文件，这时，将jar的关联去掉即可)

Appendix
Test.java

package test;

import javax.swing. * ;

public class Test extends JFrame {
     public static void main(String[] args) {
        Test impl = new Test();
        JLabel label = new JLabel( " hello world " );
        impl.add(label);
            impl.pack();
        impl.setVisible( true );
    }
}

mf.mf

Manifest-Version: 1.0
Main-Class: test.Test
<回车>

Jcat 2006-06-19 22:45 发表评论