1、 1 外文翻译 Beginning JSP, JSF, and Tomcat Web Development From Novice to Professional Material Source:http:/ Author:Giulio Zambon Jsp is a technology that lets you add dynamic content to web pages.Without jsp,you always.Have to update the appearance or the content of plain static html.Pages by hand .ev
2、en if all.You want to do is change a date or a picture,you must edit the html,file and type in your modifications.nobody is going to do it for you,whereas with jsp,you can make the content.Depend on many factors,including the time of the day,the information provided by the user,her history of intera
3、ction with your web site,and even her browser type .This capability is Essential to provide online services in which each customer is treated differently depending on Her preferences and requirements a crucial aspect of providing meaningful onlin services is For the system to be able to remember dat
4、a associated with the service and it is users that is why Databases play an essential role in dynamic . In chapter is simple hello.jsp example,you saw that request.getheader returns a string that describes the client is web browser.despite the face that the variable request is not defined anywhere,t
5、his works because tomcat defines several implicit variables: application, config, out, pagecontext, request, response, and session.the most commonly used are out and request,followed by application and session.This first line of hello.jsp is an example of a direction element,another component of jsp
6、; Directives provide tomcat with information it needs to translate the jsp page.As such directives.Are independent of specific requests.Besides page,other available directives are include and taglib.The purpose of standard action is to encapsulated activities that tomcat performs when handing.An htt
7、p request from a client .There are more than a dozen standard action ： attribute, body ,felement,fallback,forward,getProperty,include,param,params,plugin,setProperty,text,and useBean.For example,the following standard action includes in a jsp page the output of another jsp. The hello.jsp example als
8、o includes another jsp component,a scripting 2 element,which is a scriptlet delimited by the pair.All scripting elements consist of code delimited by particular sequences of characters.EL is a jsp component that gives you easy access to external object. JSP provides a mechanism that lets you define
9、custom action in which a prefix of your choise replaces the jsp of the standard actions.With the tag extension mechanism,you can create libraries of action,which you can then use in all your applications.Several custom actions have become so widely used in the programming community that sun microsys
10、tems decided to standardize them The result is JSTL.A JSP page consists of a page template,which is composed of HTML code,as well as JSP elements,such as directives,scripting elements,and standard action. which are a type of scripting element,let you embed java code in an HTML page.Every java execut
11、able whether it is a free-standing program running directly within a runtime .Environment,an applet executing inside a browser,or a servlet executing in a container such as Tomcat boils down to instantiating classes into object and executing their methods.This might not be so apparent with JSP,becau
12、se tomcat wraps every jsp page into a class of type servlet behind the scenes,bue it still applies.Java methods consist of a sequence of operations to instantiate objects,allocate memory for variables,calculate expression. A JSP page consists of a page template,which is composed of HTML code,as well
13、 as JSP elements,such as directives,scripting elements,and standard action.As wementioned inchapter1. Scriptlets,which are a type of scripting element,let you embed java code in an HTML page.Every java executable whether it is a free-standing program running directly within a runtime .Environment,an
14、 applet executing inside a browser,or a servlet executing in a container such as Tomcat boils down to instantiating classes into object and executing their methods.This might not be so apparent with JSP,because tomcat wraps every jsp page into a class of type servlet behind the scenes,bue it still a
15、pplies.Java methods consist of a sequence of operations to instantiate objects,allocate memory for variables,calculate expression,Perform assignments,or execute other methods. Java makes available primitive data type similar to the basic types of C/C+.However,there is one important,if not so apparen
16、t,difference.The precision of the numeric.Type is implementation-dependent in C,but it is guaranteed to be constant across platforms in java.Here are some examples of how you can declare variables and initialize them： String aString = “abcdxyz“; 3 int k = aString.length();/k is then set to 7 Char c
17、= aString.chatAT(4);/c is set to x Static final String NAME = “John Dod“; The final keyword in the example of declarations makes the variable unchangeable,This is how you define constants in java .The static keyword indicates that a variable is to be shared by all objects instantiated from the class
18、 within the same application.The use of static variables in jsp required some further comment.In JSP,you can declare variables in three way: The first declaration means that a new variable is created for each incoming HTTP client request； the second one means that a new variable is created for each
19、new instance of the servlet;and the third one means that the variable is shared among all instances of the servlet.Tomcat converts each JSP page into a subclass of the HTTP servlet class normally,tomcat instantiates each one of these classes only once and then creates a java thread for Each incoming
20、 request.The same servlet object is then executed within each thread . As there is a single servlet,this is no longer true if you direct tomcat to create a new servlet instance for each incoming request.Then,only the third declaration will guarantee that the variable is shared among all requests.The
21、re are no surprises with the binary operators that is,the operators that require two operands.They include the expected addition,subtraction,multiplication,division,and modulus operators,when applied to strings,the addition operator concatenates them.Besides the normal assignment operator represente
22、d by the equal sign,there is also an assignment operator for each binary one.For example,this line of code means that you take the current variable a,add to it b,and store it back into a： a += b; /same as a = a + b; The most commonly used unary operators include a minus sign,which negates what follo
23、ws,and the increment and decrement operators： a+; /same as a += 1; a-; /same as a -= 1; You can assign the value of an expression of one type to a variable of another type,but with some restriction.With numeric type ,you can only assign values to variables.For example,you can assign an int values to
24、 a variable of type long.but to 4 assign a long value to an int variable,you have to typecast the value,as in int iVar = (int)1234567L;Be careful with that!You can assign objects to variables of other types,but you can typecast a value of a superclass into a variable of a subclass type.Comparison op
25、erators are straightforward when applied to primitive data types.you have =to check for equality,!=to check for inequality,to check for“greater than,“=to check for “greater than or equal to,“ 指示提供 tomcat 将信息翻译成 JSP 页面 .这样的指示独立于特别的要求 .除了页面 ,其它可利用的指示是 include 和 taglib.标准动作的目的是在tomcat 执行客户的 http 请求的活动时
26、进行封装处理 .这里有超过 12 标准动作 :attribute、 body 、 Element、 fallback,、 forward、 getProperty、 include、param、 params、 plugin、 setProperty、 text 和 useBean.举个例子 ,以下标准动作包含在一个 JSP页面中输出的另一个 JSP. hello.JSP 的例子还包括另一个 JSP 组件 ,一个脚本元素 ,这是一个通过一对 划分的脚本小程序 .所有脚本组成的代码划分了一种特殊的的字符序列 .这是一个 JSP 组件 ,使你容易试用外部对象 . JSP提供了一种机制 ,让您自定
27、义的选择哪一个前缀代替 JSP的标准行动 .用标签扩展机制 ,你可以创造图书馆的活动 ,然后你可以使用你所有的applications.Several.定制动作已经变得如此广泛应用于编程社会 , sun microsystems决定规范他们的 JSTL.一个 JSP页面由一个网页模板、 HTML代码 ,以及 JSP 的元素组成 ,例如指令 ,脚本元素 ,标准动作 .这是一种脚本元素 ,让你7 在一个 HTML页面内嵌入 Java代码 .每个 Java 是否可执行不依赖于运行的时间环境 ,一个程序在执行一个浏览器 ,或小服务程序执行一个容器 .比如 Tomcat 可以归结为实例化类对象和执行他们
28、的方法 .这可能不会如 JSP,明显 ,因为在后台 tomcat覆盖来了每个 JSP页面中 class 类 ,而是它仍然适用 . Java 方法包括一系列的行动将被实例化对象、分配内存为变量 ,计算的表达 ,完成分配或者执行其他方法 .Java 可以提供与 C / c+原始数据类型相似的基本类型 .但是 ,有一个重要的 ,在 Java 中如果不是很明显差别 ,区别准确的数字类型是依赖于实现的 C语言中 ,但这是能保证在跨平台保持恒定 . 这里是一些如何声明变量和初始化的例子： String aString = “abcdxyz“; int k = aString.length();/k is
29、then set to 7 Char c = aString.chatAT(4);/c is set to x Static final String NAME = “John Dod“; 例子中 ,最后的关键词声明使变量不变 ,这是如何定义常数 ,在 Java,静态关键字表明一个变量 ,初始化对象在同一个类中应用 . 在 JSP中静态变量的使用有进一步的要求：可以有三种声明变量的方法： 第一个声明意味着为了每个发出请求的 HTTP客户提供一个变量；第二个意味着为每个新建小服务程序的实例提供一个新的变量；第三个意味着变量是共享小服务程序的全部可能情况 . 在正常情况下 ,tomcat终止每个
30、JSP 页面中转化为子类的 HTTP.Tomcat 仅实例化一次这些类 ,然后创建一个 Java线程 .相同的小服务程序对象在每一个线程中有一个单一的已知的小服务程序 ,如果你直接在 tomcat中创建一个新的小服务程序实例作为每个收到的请求 ,那么 ,只有三分之一可以 保证声明共享变量为所有的要求 .如无意外 ,二进制操作符需要两个操作对象 ,他们包括预期的加、减、乘、除和模数操作符 ,当应用于字符串时 , 他们的加法操作符序除正常赋值运算符所代表的等号 ,还有一个赋值运算符的二进制 .例如 ,这一行的代码意味着以当前的变量 ,加上 b,并将其存储回给 a: a += b; /same as
31、 a = a + b; 最常用的一元操作包括一个负号 ,接下来是递增和递减运算符 : a+; /same as a += 1; a-; /same as a -= 1; 你可以把一个类型的值赋给另 一个类型的变量 ,另一种类型 ,但是有一些限8 制 ,数值类型 ,你只能用变量赋值 .例如 ,你可以指定整型的变量为长整型 ,但是不能将长整型的值赋给整型 .你必须将这个值进行类型转换 .就像 intiVar =(int)1234567L;小心 !你可以指定变量对象为其他类型 ,但是但是你可以对父类的值的变量类型子类进行类型转换 . 比较运算符是直接的应用原始数据类型 .用 =表示相等 ,用！ =表
32、示不相等 ,表示”大于 “ =表示“大于等于” ,表示“小于” , =表示“小于或等于 .“没什么令人惊讶的 .然而 , 你必须小心 , 当你进行比较的 对象 ,举例说明 : String s1 = “abc“; String s2 = “abc“ String s3 = “abcd“,substring(0,3); Boolean b1 = (s1 = “abc“); Boolean b2= (s1 = “s2“); Boolean b3= (s1 = “s3“); 正如你所想 ,b1及 b2输出为“ true” ,但是 b3输出的是“ false” ,虽然 s3被赋值成“ abc” !但是
33、问题在于比较运算符不看内部的赋值 ,他们只检查是对象的实例方法是否相同 ,而不是赋值是 否相同 ,因此 ,只要你移动在“ abc”字符串 ,编译器就会提供关于相同的实例常量字符串 .如预期所想 ,当你创建出不同的实例“ abc” ,验证等于“ fail” . 学习中得到的教训是： ,如果你比较内部的对象 ,你必须使用例子中的这个“相等”的这个方法 ,s1.equals(s3)会返回“ true” . 结构化查询语言 (SQL)是使用最广泛的 DBMSs交互语言 .这个附件的目的并不是提供一个综合全面的 SQL手册 ,而是要列出并解释最常见的概念、条款和声明 .大多数的 DBMSs 都不支持整个
34、 SQL标准 ,而且 ,厂商有时候加不标准的元素 , 在实践中 ,防止 DBMSs 溢出 , 我们会限制自己标准规范基础来帮助你识别关键字 . SQL 技术 数据表是由行和列组成的组织 .这是一个自然的方法组织数据 ,你可能通过使用电子表格熟悉它 ,不过 ,虽然有一些相似之处 ,一个数据库表不是一个excel工作表 .例如 :电子表格 ,你可以在单元格中指定个人数据类型 ,而在数据库中 ,所有的列的数据类型都相同 .列定义 ,每个单元格都有他们的名字和类型 ,代表数据结构允许的表格 .例如 ,员工表可能包含列名首名末名 ,社会安全号码包含文字串 , columns 函数被命名为 Employe
35、eNumber 和 YearSalary,其包含数字 ,包含日期命 .数据与相关各员工将都存入一排 . 交易值 交易值应多关注一些 , 因为他们在数据库中代表操作符一个很重要的概念 .交易表明一系列的数据库操作没有中断的进行 , 在中间没有任何其他潜在操作 .9 要弄懂这些 ,你必须在术语中访问相同的表格 . 检索 SELECT（检索）是一个或多个表格和视图中检索数据 .在某种程度上 , SELECT的复杂性是由于有两种方法可以选择：检索实际资料的结果或获取的数据 ,应用功能更糟糕的是 , 更糟糕的是 ,一些元素 ,仅适用于两种方式中的一种来解释如何使用 SELECT.我们要分两种运作模式 .
36、 创建数据库 CREATE DATABASE（创建数据库）是创建一个新的、空的数据库 .当与 Java和 JSP一起使用 SQL时 ,你需要指定一个统一的字符编码标准的字符集 ,每个字符被存储在一个可变数目的字节 .事实上 ,有几个 统一的字符编码标准 ,但 utf8是目前应用最广泛的也是与 ASCIL最类似的标准 , 同样地 ,他是英语语系的最好选择 ,你不需要用到 统一的字符编码标准 ,默认就好了 . 插入 INSERT（插入）是在现有的表或视图中存储一个或多个行 . 终止 DROP（终止）是当你想要删除一个 数据库、一个表格一个指针或一个视图时用来声明的 . 转换表格 ALTER TABLE（转换表格）是用来改变表格现有的结构的 . 修改 UPDATE（修改）是用来修改现有表或视图中的一个或多个的数据 .
