源代码下载（三个样例工程Maven版本Q?xfire-src.zip
相关lib文g请到XFire官方|站Q见参考） 下蝲发布版本?/p>
目录
实现功能与特? 2
实现功能与特?/h1>
- ZJ2EEq_的Web Service服务
- 开发方便，配置?
- 设计接口
- 实现服务
- 配置暴露接口
- XFire自动生成对应的wsdl
- 支持高详细配置
- 与Spring无缝集成
q行环境
- JDK 1.4+
- Tomcat 4.0+ / WebLogic 8.1 Q需要特D配|，见附录）未测试其他环?/li>
- 其他包依赖参?http://xfire.codehaus.org/Dependency+Guide
开发^?/h1>
- Eclipse WTP 1.5 q_IDEQ?a >www.eclipse.org/webtools/
- XFire 1.2.6 http://xfire.codehaus.org/Home
- 可以选择安装XFire for Eclipse插gQ可以添加XFire相关cdQ根据WSDL生成代码?a >http://xfire.codehaus.org/Eclipse+Plugin
- JDK 1.4.2 http://java.sun.com/products/archive/
- Tomcat 5.0.28 http://tomcat.apache.org/download-55.cgi#5.0.28
实施步骤
概述
- 建立一个Java Project用于Domain实体和Web Service接口Q这个工E的输出是一个jar包，为Web Service工程和Web Service Client׃n?/li>
- 建立WTP动态WEB工程部vWeb Service
- 建立Java Project使用Web Service (Web Service Client)
新徏Java Project
- 建立普通Java Project 以下UCؓcommon工程
- 如果使用MavenQ项目依?/li>
- 设计接口
- 实现服务
- 配置暴露接口
- XFire自动生成对应的wsdl
- 支持高详细配置
- Eclipse WTP 1.5 q_IDEQ?a >www.eclipse.org/webtools/
- XFire 1.2.6 http://xfire.codehaus.org/Home
- 可以选择安装XFire for Eclipse插gQ可以添加XFire相关cdQ根据WSDL生成代码?a >http://xfire.codehaus.org/Eclipse+Plugin
- JDK 1.4.2 http://java.sun.com/products/archive/
- Tomcat 5.0.28 http://tomcat.apache.org/download-55.cgi#5.0.28
实施步骤
概述
- 建立一个Java Project用于Domain实体和Web Service接口Q这个工E的输出是一个jar包，为Web Service工程和Web Service Client׃n?/li>
- 建立WTP动态WEB工程部vWeb Service
- 建立Java Project使用Web Service (Web Service Client)
新徏Java Project
- 建立普通Java Project 以下UCؓcommon工程
- 如果使用MavenQ项目依?/li>
<dependency>
<groupId>javax.mail</groupId>
<artifactId>mail</artifactId>
<version>1.4</version>
</dependency>
- 普通情况需要加入如下lib
activation-1.1.jar
mail-1.4.jar
- ~写c?org.ave7.xfire.domain.User
org.ave7.xfire.domain.User.java
package org.ave7.xfire.domain;
import java.io.Serializable;
import java.util.Date;
public class User implements Serializable {
private static final long serialVersionUID = 6517808321041980976L;
private Long userId;
private String accountId;
private String userName;
private Date lastLogin;
public String getAccountId() {
return accountId;
}
public void setAccountId(String accountId) {
this.accountId = accountId;
}
public Date getLastLogin() {
return lastLogin;
}
public void setLastLogin(Date lastLogin) {
this.lastLogin = lastLogin;
}
public Long getUserId() {
return userId;
}
public void setUserId(Long userId) {
this.userId = userId;
}
public String getUserName() {
return userName;
}
public void setUserName(String userName) {
this.userName = userName;
}
}
import java.io.Serializable;
import java.util.Date;
public class User implements Serializable {
private static final long serialVersionUID = 6517808321041980976L;
private Long userId;
private String accountId;
private String userName;
private Date lastLogin;
public String getAccountId() {
return accountId;
}
public void setAccountId(String accountId) {
this.accountId = accountId;
}
public Date getLastLogin() {
return lastLogin;
}
public void setLastLogin(Date lastLogin) {
this.lastLogin = lastLogin;
}
public Long getUserId() {
return userId;
}
public void setUserId(Long userId) {
this.userId = userId;
}
public String getUserName() {
return userName;
}
public void setUserName(String userName) {
this.userName = userName;
}
}
- ~写接口 org.ave7.xfire.ws.UserService
org.ave7.xfire.ws.UserService.java
package org.ave7.xfire.ws;
import org.ave7.xfire.domain.User;
public
interface UserService {
public User queryUserByAccoutId(String accountId);
public
void createUser(User user);
}
package org.ave7.xfire.ws;
import org.ave7.xfire.domain.User;
public
interface UserService {
public User queryUserByAccoutId(String accountId);
public
void createUser(User user);
}
新徏WTP动态WEB工程
- 配置WTP加入Tomcat Server Runtime
- 选择Windows -> Preference
- 在左侧选择Server->Installed Runtime dTomcat
- 新徏工程Q选择Dynamic Web Project 输入Project Name: XFireService
- 讄q行环境为Dynamic Web Module 2.3 , JDK 1.4
- 如果需要结合MavenQ请如下配置Q否则用默认即?br>
- 如果使用Mavenh入如下依赖以及之前的Common工程Q否则根据后面的列表复制lib文g到对应目?/li>
<dependency>
<groupId>org.codehaus.xfire</groupId>
<artifactId>xfire-aegis</artifactId>
<version>1.2.4</version>
</dependency>
<dependency>
<groupId>org.codehaus.xfire</groupId>
<artifactId>xfire-spring</artifactId>
<version>1.2.4</version>
<dependency>
<groupId>xalan</groupId>
<artifactId>xalan</artifactId>
<version>2.7.0</version>
</dependency>
Lib文g列表
xbean-2.2.0.jar
qdox-1.5.jar
commons-attributes-api-2.1.jar
ant-1.5.jar
wstx-asl-3.2.0.jar
stax-utils-20040917.jar
commons-httpclient-3.0.jar
spring-1.2.6.jar
XmlSchema-1.1.jar
stax-api-1.0.1.jar
jaxen-1.1-beta-9.jar
xfire-annotations-1.2.4.jar
xfire-aegis-1.2.4.jar
xfire-core-1.2.4.jar
xfire-spring-1.2.4.jar
xfire-xmlbeans-1.2.4.jar
jdom-1.0.jar
xbean-spring-2.7.jar
wsdl4j-1.6.1.jar
commons-beanutils-1.7.0.jar
activation-1.1.jar
mail-1.4.jar
commons-codec-1.3.jar
xmlParserAPIs-2.6.2.jar
xercesImpl-2.6.2.jar
junit-3.8.1.jar
commons-logging-1.0.4.jar
xalan-2.7.0.jar
实现服务
org.ave7.xfire.ws.UserServiceImpl.java
package org.ave7.xfire.ws;
import java.rmi.RemoteException;
import java.util.Date;
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.ave7.xfire.domain.User;
public
class UserServiceImpl implements UserService {
private
static
final Log log = LogFactory.getLog(UserServiceImpl.class);
public
void createUser(User user) throws RemoteException {
log.debug(“createUser user=” + user);
}
public User queryUserByAccoutId(String accountId) throws
RemoteException {
log.debug(“accountId=” + accountId);
User user = new User();
user.setAccountId(“testAccount”);
user.setLastLogin(new Date());
user.setUserName(“试用户“);
user.setUserId(new Long(123L));
return user;
}
}
import java.rmi.RemoteException;
import java.util.Date;
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.ave7.xfire.domain.User;
public
class UserServiceImpl implements UserService {
private
static
final Log log = LogFactory.getLog(UserServiceImpl.class);
public
void createUser(User user) throws RemoteException {
log.debug(“createUser user=” + user);
}
public User queryUserByAccoutId(String accountId) throws
RemoteException {
log.debug(“accountId=” + accountId);
User user = new User();
user.setAccountId(“testAccount”);
user.setLastLogin(new Date());
user.setUserName(“试用户“);
user.setUserId(new Long(123L));
return user;
}
}
利用Spring、XFire装配与暴露服?/h2>
- 在web.xml配置相关lg
<?xml version=“1.0″ encoding=“UTF-8″?>
<!DOCTYPE web-app PUBLIC “-//Sun Microsystems, Inc.//DTD Web Application 2.3//EN”
“http://java.sun.com/dtd/web-app_2_3.dtd”>
<web-app id=“WebApp_ID”>
<display-name>XFireService</display-name>
<context-param>
<param-name>contextConfigLocation</param-name>
<param-value>classpath:applicationContext*.xml</param-value>
</context-param>
<listener>
<listener-class>
org.springframework.web.context.ContextLoaderListener
</listener-class>
</listener>
<servlet>
<servlet-name>xfire</servlet-name>
<servlet-class>
org.codehaus.xfire.spring.XFireSpringServlet
</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>xfire</servlet-name>
<url-pattern>/service/*</url-pattern>
</servlet-mapping>
</web-app>
- 在applicationContext.xml配置相关服务
<?xml version=“1.0″ encoding=“UTF-8″?>
<!DOCTYPE beans PUBLIC “-//SPRING//DTD BEAN//EN”
“http://www.springframework.org/dtd/spring-beans.dtd”>
<beans>
<import resource=“classpath:org/codehaus/xfire/spring/xfire.xml” />
<bean id=“baseWebService”
class=“org.codehaus.xfire.spring.remoting.XFireExporter”
lazy-init=“false” abstract=“true”>
<property name=“serviceFactory” ref=“xfire.serviceFactory” />
<property name=“xfire” ref=“xfire” />
</bean>
<bean id=“userWS” class=“org.ave7.xfire.ws.UserServiceImpl”></bean>
<bean id=“userService” parent=“baseWebService”>
<property name=“serviceBean” ref=“userWS” />
<property name=“serviceClass”
value=“org.ave7.xfire.ws.UserService” />
</bean>
</beans>
试q访问服?/h2>
- 查lib文g夹，Maven用户注意d对common工程的依赖，其他情况hcommon工程导出的jar包复制到web-inf/lib目录
- 在WTP中添加服务器Q部|应?br>
- 在浏览器中输入类?http://localhost:8080/XFireService/service 应看?br>
- 点击wsdl http://localhost:8080/XFireService/service/UserService?wsdl 看到
如果q一步出?00错误Q请查是否有xalan.jar?/li>
- 在WTP中利用Web Service Explore试SOAP方式Q在WTP工具栏选择
最右侧按钮
- 点击右上角进入WSDL page
- 点击WSDL Main节点输入服务wsdl地址Q点?br>
- 列出所有的可用服务Q选择服务试
- 试queryUserByAccountId
- 点击l果中的Source可以看到SOAP报文
利用XFire实现客户?/h2>
- 新徏一个普通Java工程Qlib中引用XFire相关?/li>
<!DOCTYPE web-app PUBLIC “-//Sun Microsystems, Inc.//DTD Web Application 2.3//EN”
“http://java.sun.com/dtd/web-app_2_3.dtd”>
<web-app id=“WebApp_ID”>
<display-name>XFireService</display-name>
<context-param>
<param-name>contextConfigLocation</param-name>
<param-value>classpath:applicationContext*.xml</param-value>
</context-param>
<listener>
<listener-class>
org.springframework.web.context.ContextLoaderListener
</listener-class>
</listener>
<servlet>
<servlet-name>xfire</servlet-name>
<servlet-class>
org.codehaus.xfire.spring.XFireSpringServlet
</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>xfire</servlet-name>
<url-pattern>/service/*</url-pattern>
</servlet-mapping>
</web-app>
<!DOCTYPE beans PUBLIC “-//SPRING//DTD BEAN//EN”
“http://www.springframework.org/dtd/spring-beans.dtd”>
<beans>
<import resource=“classpath:org/codehaus/xfire/spring/xfire.xml” />
<bean id=“baseWebService”
class=“org.codehaus.xfire.spring.remoting.XFireExporter”
lazy-init=“false” abstract=“true”>
<property name=“serviceFactory” ref=“xfire.serviceFactory” />
<property name=“xfire” ref=“xfire” />
</bean>
<bean id=“userWS” class=“org.ave7.xfire.ws.UserServiceImpl”></bean>
<bean id=“userService” parent=“baseWebService”>
<property name=“serviceBean” ref=“userWS” />
<property name=“serviceClass”
value=“org.ave7.xfire.ws.UserService” />
</bean>
</beans>
- 查lib文g夹，Maven用户注意d对common工程的依赖，其他情况hcommon工程导出的jar包复制到web-inf/lib目录
- 在WTP中添加服务器Q部|应?br>
- 在浏览器中输入类?http://localhost:8080/XFireService/service 应看?br>
- 点击wsdl http://localhost:8080/XFireService/service/UserService?wsdl 看到
如果q一步出?00错误Q请查是否有xalan.jar?/li> - 在WTP中利用Web Service Explore试SOAP方式Q在WTP工具栏选择 最右侧按钮
- 点击右上角进入WSDL page
- 点击WSDL Main节点输入服务wsdl地址Q点?br>
- 列出所有的可用服务Q选择服务试
- 试queryUserByAccountId
- 点击l果中的Source可以看到SOAP报文
利用XFire实现客户?/h2>
- 新徏一个普通Java工程Qlib中引用XFire相关?/li>
如果使用Mavend如下依赖以及对common工程的引?/p>
<dependency>
<groupId>org.codehaus.xfire</groupId>
<artifactId>xfire-aegis</artifactId>
<version>1.2.4</version>
</dependency>
普通Java工程d如下lib以及对common工程的引?/p>
activation-1.1.jar
commons-codec-1.3.jar
commons-httpclient-3.0.jar
commons-logging-1.0.4.jar
jaxen-1.1-beta-9.jar
jdom-1.0.jar
junit-3.8.1.jar
mail-1.4.jar
stax-api-1.0.1.jar
stax-utils-20040917.jar
wsdl4j-1.6.1.jar
wstx-asl-3.2.0.jar
xercesImpl-2.6.2.jar
xfire-aegis-1.2.4.jar
xfire-core-1.2.4.jar
xmlParserAPIs-2.6.2.jar
XmlSchema-1.1.jar
- ~写客户端程?/li>
org.ave7.xfire.client.MyClient.java
package org.ave7.xfire.client;
import java.net.MalformedURLException;
import java.rmi.RemoteException;
import org.ave7.xfire.domain.User;
import org.ave7.xfire.ws.UserService;
import org.codehaus.xfire.client.XFireProxyFactory;
import org.codehaus.xfire.service.Service;
import org.codehaus.xfire.service.binding.ObjectServiceFactory;
public
class MyClient {
public
static
void main(String[] args) {
try {
Service serviceModel = new ObjectServiceFactory()
.create(UserService.class);
UserService service = (UserService) new XFireProxyFactory().create(
serviceModel,
“http://localhost:8080/XFireService/service/UserService”);
User user = service.queryUserByAccoutId(“123″);
System.out
.println(“userId=” + user.getUserId() + “, userName=”
+ user.getUserName() + “, lastLogin=”
+ user.getLastLogin());
} catch (MalformedURLException e) {
e.printStackTrace();
} catch (RemoteException e) {
e.printStackTrace();
}
}
}
import java.net.MalformedURLException;
import java.rmi.RemoteException;
import org.ave7.xfire.domain.User;
import org.ave7.xfire.ws.UserService;
import org.codehaus.xfire.client.XFireProxyFactory;
import org.codehaus.xfire.service.Service;
import org.codehaus.xfire.service.binding.ObjectServiceFactory;
public
class MyClient {
public
static
void main(String[] args) {
try {
Service serviceModel = new ObjectServiceFactory()
.create(UserService.class);
UserService service = (UserService) new XFireProxyFactory().create(
serviceModel,
“http://localhost:8080/XFireService/service/UserService”);
User user = service.queryUserByAccoutId(“123″);
System.out
.println(“userId=” + user.getUserId() + “, userName=”
+ user.getUserName() + “, lastLogin=”
+ user.getLastLogin());
} catch (MalformedURLException e) {
e.printStackTrace();
} catch (RemoteException e) {
e.printStackTrace();
}
}
}
- q行。控制台打印输出
2007-8-16 10:25:52 org.codehaus.xfire.aegis.type.DefaultTypeMappingRegistry crea
teTypeCreator
信息: Couldn’t find Java 5 module on classpath. Annotation mappings will not be su
pported.
userId=123, userName=试用户, lastLogin=Thu Aug 16 10:25:53 CST 2007
扩展主题
利用MTOM传输二进制对象（文gQ?/h2>
MTOM是XFire的一个组Ӟ可以协助利用压羃{手D|快的在网l上传输base64的SOAP对象
MTOM以及aegis默认支持如下几种java对象的数?/p>
- byte[]
- javax.activation.DataHandler
- javax.activation.DataSource
- 配置启用MTOM
在Spring配置文g中需要MTOM的服务中加入如下配置
<bean id=“userService” parent=“baseWebService”>
<property name=“serviceBean” ref=“userWS” />
<property name=“serviceClass”
value=“org.ave7.xfire.ws.UserService” />
<property name=”properties”>
<map>
<entry key=”mtom-enabled” value=”true” />
</map>
</property>
</bean>
<property name=“serviceBean” ref=“userWS” />
<property name=“serviceClass”
value=“org.ave7.xfire.ws.UserService” />
<property name=”properties”>
<map>
<entry key=”mtom-enabled” value=”true” />
</map>
</property>
</bean>
- 在客L~写传输E序
Service serviceModel = new ObjectServiceFactory()
.create(UserService.class);
UserService service = (UserService) new XFireProxyFactory().create(
serviceModel,
“http://localhost:8080/XFireService/service/UserService”);
Client client = Client.getInstance(service);
client.setProperty(“mtom-enabled”, “true”);
client.setProperty(HttpTransport.CHUNKING_ENABLED, “true”);
User user = service.queryUserByAccoutId(“123″);
System.out
.println(“userId=” + user.getUserId() + “, userName=”
+ user.getUserName() + “, lastLogin=”
+ user.getLastLogin());
ByteArrayDataSource byteData = new ByteArrayDataSource(
“Test Sending Byte”.getBytes(), “text/plain; charset=UTF-8″);
service.transferDataSource(byteData);
.create(UserService.class);
UserService service = (UserService) new XFireProxyFactory().create(
serviceModel,
“http://localhost:8080/XFireService/service/UserService”);
Client client = Client.getInstance(service);
client.setProperty(“mtom-enabled”, “true”);
client.setProperty(HttpTransport.CHUNKING_ENABLED, “true”);
User user = service.queryUserByAccoutId(“123″);
System.out
.println(“userId=” + user.getUserId() + “, userName=”
+ user.getUserName() + “, lastLogin=”
+ user.getLastLogin());
ByteArrayDataSource byteData = new ByteArrayDataSource(
“Test Sending Byte”.getBytes(), “text/plain; charset=UTF-8″);
service.transferDataSource(byteData);
附录
XFire在WebLogic 8.1中的配置
- Add the QName JAR file (qname.jar) into the WEB-INF/lib folder in your WAR file
- Add a file weblogic.xml into the WEB-INF folder in your WAR file
<!DOCTYPE weblogic-web-app PUBLIC
“-//BEA Systems, Inc.//DTD Web Application 8.1//EN”
“http://www.bea.com/servers/wls810/dtd/weblogic810-web-jar.dtd”>
<weblogic-web-app>
<container-descriptor>
<prefer-web-inf-classes>true</prefer-web-inf-classes>
</container-descriptor>
</weblogic-web-app>
“-//BEA Systems, Inc.//DTD Web Application 8.1//EN”
“http://www.bea.com/servers/wls810/dtd/weblogic810-web-jar.dtd”>
<weblogic-web-app>
<container-descriptor>
<prefer-web-inf-classes>true</prefer-web-inf-classes>
</container-descriptor>
</weblogic-web-app>
QName JAR file (qname.jar) http://docs.codehaus.org/download/attachments/27836/qname.jar?version=1
参?/h1>
- File Transfers using SOAP XFire http://blogs.opensymphony.com/plightbo/2006/04/file_transfers_using_soap_xfir.html
- XFire生火指南
http://wiki.springside.org.cn/display/springside/XFire
- XFire官方|站
http://xfire.codehaus.org/Home
http://wiki.springside.org.cn/display/springside/XFire
http://xfire.codehaus.org/Home
XFire On WebLogic 8.1
http://docs.codehaus.org/display/XFIRE/XFire+on+WebLogic+8.1
]]>
我不明白Q服务器端的E序p大么？
Z么都跑来对JavaScript动一堆手脚?br>
有h说的好，JSF是ASP.net in JAVA?br>N把前台后台Z谈，提供些预定义的控件就是良好的框架么？
]]>
一些功能列表：
- explore the DOM tree and find elements on the page
- disable IE settings, view information
- outline elements,
- control images
- resize pages to common screen resolutions
- validate against existing standards and provides pointers to W3C specs
http://www.microsoft.com/downloads/details.aspx?FamilyID=e59c3964-672d-4511-bb3e-2d5e1db91038&displaylang=en
]]>
]]>
- A variable holds a value, while an object reference variable points to the memory that holds the object.
- The short-circuit logical operators && and || operate only on boolean operands. For example, the expression
9&&7 will not compile. Understand the difference between short-circuit logical operators and bitwise
operators. - If the first expression of a && operator is false, the second expression is not evaluated, and if the first
expression of a || operator is true, the second expression is not evaluated.
Look Out
- Be on guard for words that are only slightly different from the Java keywords, such as synchronize instead of synchronized, implement instead of implements, and protect instead of protected.
- Whether an array stores primitive variables or object references, the array itself is always an object.
- It is illegal to include the array size in the array declaration.
- Division by zero generates a runtime ArithmeticException only if the operands are integers. In case of float and double, the result of division by zero is infinity.
- The result of the modulo operator always carries the sign of the first operand (i.e. the one before the operator);
you can ignore the sign of the second operand. - You cannot instantiate an enum by using the new operator.
Memorize
- Know the Java language keywords.
- Know the range of values for all primitive data types.
- All primitive data types except boolean and char are signed.
- The first character of an identifier must be a letter, a dollar sign ($), or an underscore (_). Characters other than the first character in an identifier may be a letter, a dollar sign, an underscore, or a digit.
]]>
- The method name and return type are mandatory in a method declaration. Even though you are not required to specify a modifier in a method declaration, the default modifier is assigned to the method, if you don’t declare one.
- A static variable belongs to the class and not to a particular instance of the class, and therefore is initialized when the class is loaded, and before the class is instantiated.
- Because a static method belongs to a class and not to a particular instance of the class, it cannot access the nonstatic methods and variables of the class in which it is defined.
- An instance of an inner class can only exist in an instance of the outer class, and has direct access to all the instance variables and methods of the outer instance.
- If you make a super call or a this call, it must be in the beginning of a constructor. That means you can make either a super call or a this call, but not both.
Look Out
- The variable-length parameters list must appear last in the parentheses of a method and it consists of a data type, three dots, and a name, in that order.
- A Java class cannot inherit from more than one class, but it can inherit from one class and one or more interfaces.
- The class that inherits from an interface must provide implementation for all the methods that are declared in the interface if the class is not abstract.
- An interface can extend another interface but it cannot implement another interface or a class.
Memorize
- If you do not provide any constructor for a class you write, the compiler provides the default constructor for that class. If you write at least one constructor for the class, the compiler provides no constructor.
- If you don not make a this or a super call in the beginning of a constructor, the compiler places a super() call there.
- You use the keyword extends to write a derived class that inherits from a parent class, and use the keyword implements to write a class that inherits from an interface.
- The methods in an interface are inherently public and abstract, and the variables in the interface are inherently public, final, and static.
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- Plan an agenda.
- Define key business drivers.
- Define key success facts.
- Work out persona.
- Work out Scenario.
- High level architecture
- High level design
- Development
- QA
- Deployment
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也许你已l学会了一门计机语言Q也怽会写一D不错的E序?
也许你在嘈杂的环境用不费力的可以用熟悉的IDE完成一个项目?
不过Q你q在? - * /?做所有的计算么？
q个W记是Z写出更加正确的程序，小的一个学习过E?
我不ȝ复杂的道理，只记录用得上的方案?
出现的一切代码都使用Java语言?
正确的计过E导致错误的计算l果
关于基本数D中的一些陷?
点数和实数
当早期的Fortran和algol创造出realq个关键字时Q你q真以ؓ那么是实敎ͼ不过说真的，你被骗了?
所以到了CQ我们拥有了float?
那么他们到底有什么不同呢Q?
单地?
System.out.println(”Value of 1/3: ” + (1/3f))
输?
Value of 1/3: 0.33333334
很简单，q是很早之前您就知道的四舍五入。当时我们只是那无法写完的@环在U怸划下一?#8221;?#8221;Q然后非常开心可以少写几个字W。如果你有一个负责Q的数学老师Q他Q她Q就会反复的叮咛你，要小心，计算时候要保留l果_ֺ往后一位的数倹{?
当这一切轮C计算机，我们叫它Q?
舍入误差
舍入误差有时相当惊h。对1/3q加840ơ，你会得到279.9915Q本应当?80Q，如何惊hQ我们会在下面看到?
不过有意思的事情Q和时候的情Ş不一P舍入误差q不是由于不能除或者是无理数造成的，cM?/5的数字连加之后也有误差。这是因为绝大多? 计算机是Z2q制体系的，所以IBM有用于商业计的10q制计算机。简单的事实是利用float表达?的幂ơ，在精度范围是没有舍入误差的?
l出常用定义Q?
作如下计，你会期待怎样的结果呢Q?
别偷懒，用你久远的口能力，很容易就可以得出Q它本来应该?。而事实上Q我们伟大的计算机的{案?222784.0
Z么？
因ؓQ?0000001/20000000的时候，{案本应该是0.50000005Q由于舍入误差，我们得到?.5000006?
接下来我们减?.5的时候，得到的应当是0.00000006Q这P我们׃׃所有的正确的数?
更糟p的是，计算Z实际得到的值是5.9604645e-8?
因此Q您的存ƾ户头上可能会^白无故减?222784元。只因ؓ银行军_向你支付利息之后Q调整了汇率?
呃，q一ơ，我们叫它Q?
相消误差——两个非常相q的值相减时Q如果消Ml大多数有效数|那么׃发生相消误差?br>舍入误差——是_值和其可表达g间的差倹{?
如果q有什么要说的Q那是Q?br>
Double比float 更接q实敎ͼ貌似不需要我说?br>点q算不遵守代数定?
比如Qa = 1.0, b = 3.0e-8, c = 4.0e-8
那么Q?nbsp; (a+b)+c = 1.0
a+(b+c) = 1.0000001
不过加法和乘法还是满交换律的?
下一ơ：轮到了整数?
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因ؓ要还换空间了Q终于可以ؓ自己的网站写JavaE序了，刚好老师要我ȝ一下，提供一个即插即用的Ajax JAVA环境?
汗~~不过单美Q我开心的说一下吧?
框架选择汇?
- Ajax toolkit: Dojo http://dojotoolkit.org/
- Communication: DWR http://getahead.ltd.uk/dwr/
- Presentation: Struts 2 http://struts.apache.org/2.x/ / WebWork http://www.opensymphony.com/webwork/
- IoC: Spring http://www.springframework.org/
- Persistence: Hibernate http://www.hibernate.org/ or iBatis http://ibatis.apache.org/
选择理由
Dojo
我最q是Dojo。Dojo提供了丰富的Widget和不断增加的教程文。拥有了IBM和SUN的官Ҏ持。更重要的是QDojo不止为Java设计QDojo是一个通用的^収ͼq意味着Q所有最新的技术都可以UL到Dojo上面来，而你q不需要重新学习?
Dojo最大的q是，启动~慢Q官方网站在|络质量不好的时候会有死机的感觉。不q依然记?.3?.4的巨大惊喜。我怿随着Dojo的成熟，对其的学习是一U保值的投资?
DWR
q是目前几个框架中，我唯一没有在实际项目中使用q的。之前用Dojo和WW写程序的时候，使用JSON作ؓ数据 媒介Q没有用RPCQ。写了很多代码来负责同步JSON与JAVA对象。目前看来DWR可以很好的解册个问题。而且Q随着Annotation的流行，q配|都不用了?
Struts2 / WW
目前没有用过Struts 2不过从前wWW的表现来看，l对是开发速度之选。丰富的扩展支持Q良好的接口设计Qؓ易变的Web环境提供了舒适的开发体验。再加上Apache的大名，那就素质量的保证啊。虽然有Ajax支持的鸡肋（T_T原谅我，我是真的不会用那个）。Struts2同样开始支持Annotation配置Q真是ؓ我省心啊?
Spring
Spring is coming?.
没有理由Q只要不用EJBQ那么只有Spring才是J2EE的选择Q良好的扩展性，无所不在的简z。M记怎么说来着Q和谐美啊。Spring是和谐Q让那一片一片菱角分明的框架l合的天衣无~。总而言之一句话QSpring是端午节的p米啊。（那谁是粽子叶呢？Q?
Hibernate ?iBatis
其实持久层的选择p省重一点了?
Hibernate很方便，方便到太Ҏ犯错误。所以我把iBatis列进去，q是性能和健壮性的考虑?
我明白Hibernate有多么方便，如果两三个月p交付一个项目，Hibernate能够让你忘掉SQL的存在。但是要做一个逻辑复杂的SNS站点QiBatis无疑更轻巧更考验才智?
以上Q再加上Acegi和axis2Q暂时没打算用）Q开心的玩Java AJAX?/p>