6.转换器和格式化

1.Converter:转换器：可以在应用程序的任意层中使用

2.Formatter格式化：专门为Web设计

二者都可以将一种对象转换成另一种对象类型

1.Converter

必须实现org.springframework.core.convert.converter.Converter

public interface Converter<S,T>

S:是源类型

T：是目标类型

在类Body中，需要编写一个来自Converter接口的convert方法实现。

T convert(S source);

 1 package app06a.converter;
 2 
 3 import java.text.ParseException;
 4 import java.text.SimpleDateFormat;
 5 import java.util.Date;
 6 
 7 import org.springframework.core.convert.converter.Converter;
 8 
 9 public class StringToDateConverter implements Converter<String, Date> {
10 
11     private String datePattern;
12 
13     public StringToDateConverter(String datePattern) {
14         this.datePattern = datePattern;
15     }
16 
17     @Override
18     public Date convert(String s) {
19         try {
20             SimpleDateFormat dateFormat = new SimpleDateFormat(datePattern);
21             dateFormat.setLenient(false);
22             return dateFormat.parse(s);
23         } catch (ParseException e) {
24             // the error message will be displayed when using <form:errors>
25             throw new IllegalArgumentException(
26                     "invalid date format. Please use this pattern""
27                             + datePattern + """);
28         }
29     }
30 }

为了使用SpringMVC应用程序中定制Converter

需要在Spring MVC配置文件中编写converterService bean

Bean的类名称为org.springframework.context.support.ConversionServiceFactoryBean

这个Bean必须包含一个converts属性，它将列出要在应用程序中使用所有定制的Converter

要给<mvc:annotation-driven conversion-service="conversionService"/>

conversion-service属性赋bean名称

 1 <?xml version="1.0" encoding="UTF-8"?>
 2 <beans xmlns="http://www.springframework.org/schema/beans"
 3     xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
 4     xmlns:p="http://www.springframework.org/schema/p"
 5     xmlns:mvc="http://www.springframework.org/schema/mvc"
 6     xmlns:context="http://www.springframework.org/schema/context"
 7     xsi:schemaLocation="
 8         http://www.springframework.org/schema/beans
 9         http://www.springframework.org/schema/beans/spring-beans.xsd
10         http://www.springframework.org/schema/mvc
11         http://www.springframework.org/schema/mvc/spring-mvc.xsd     
12         http://www.springframework.org/schema/context
13         http://www.springframework.org/schema/context/spring-context.xsd">
14         
15     <context:component-scan base-package="app06a.controller"/>
16      
17     <mvc:annotation-driven conversion-service="conversionService"/>
18     <mvc:resources mapping="/css/**" location="/css/"/>
19     <mvc:resources mapping="/*.html" location="/"/>
20     
21     <bean id="viewResolver" class="org.springframework.web.servlet.view.InternalResourceViewResolver">
22         <property name="prefix" value="/WEB-INF/jsp/"/>
23         <property name="suffix" value=".jsp"/>
24     </bean>
25     
26     <bean id="conversionService" 
27             class="org.springframework.context.support.ConversionServiceFactoryBean">
28         <property name="converters">
29             <list>
30                 <bean class="app06a.converter.StringToDateConverter">
31                     <constructor-arg type="java.lang.String" value="MM-dd-yyyy"/>
32                 </bean>
33             </list>
34         </property>
35     </bean>
36 </beans>

Employee类

 1 package app06a.domain;
 2 
 3 import java.io.Serializable;
 4 import java.util.Date;
 5 
 6 public class Employee implements Serializable {
 7     private static final long serialVersionUID = -908L;
 8 
 9     private long id;
10     private String firstName;
11     private String lastName;
12     private Date birthDate;
13     private int salaryLevel;
14 
15     public long getId() {
16         return id;
17     }
18 
19     public void setId(long id) {
20         this.id = id;
21     }
22 
23     public String getFirstName() {
24         return firstName;
25     }
26 
27     public void setFirstName(String firstName) {
28         this.firstName = firstName;
29     }
30 
31     public String getLastName() {
32         return lastName;
33     }
34 
35     public void setLastName(String lastName) {
36         this.lastName = lastName;
37     }
38 
39     public Date getBirthDate() {
40         return birthDate;
41     }
42 
43     public void setBirthDate(Date birthDate) {
44         this.birthDate = birthDate;
45     }
46 
47     public int getSalaryLevel() {
48         return salaryLevel;
49     }
50 
51     public void setSalaryLevel(int salaryLevel) {
52         this.salaryLevel = salaryLevel;
53     }
54 
55 }

Controller

有了StringToDateConverter converter，就不需要劳驾

controller类将字符串转换成日期了

 1 package app06a.controller;
 2 
 3 import org.apache.commons.logging.Log;
 4 import org.apache.commons.logging.LogFactory;
 5 import org.springframework.ui.Model;
 6 import org.springframework.validation.BindingResult;
 7 import org.springframework.validation.FieldError;
 8 import org.springframework.web.bind.annotation.ModelAttribute;
 9 import org.springframework.web.bind.annotation.RequestMapping;
10 
11 import app06a.domain.Employee;
12 
13 @org.springframework.stereotype.Controller
14 
15 public class EmployeeController {
16     
17     private static final Log logger = LogFactory.getLog(ProductController.class);
18     
19     @RequestMapping(value="employee_input")
20     public String inputEmployee(Model model) {
21         model.addAttribute(new Employee());
22         return "EmployeeForm";
23     }
24 
25     @RequestMapping(value="employee_save")
26     public String saveEmployee(@ModelAttribute Employee employee, BindingResult bindingResult,
27             Model model) {
28         if (bindingResult.hasErrors()) {
29             FieldError fieldError = bindingResult.getFieldError();
30             logger.info("Code:" + fieldError.getCode() 
31                     + ", field:" + fieldError.getField());
32             return "EmployeeForm";
33         }
34         
35         // save employee here
36         
37         model.addAttribute("employee", employee);
38         return "EmployeeDetails";
39     }
40 }

 1 <%@ taglib prefix="form" uri="http://www.springframework.org/tags/form" %>
 2 <%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c" %>
 3 <!DOCTYPE HTML>
 4 <html>
 5 <head>
 6 <title>Add Employee Form</title>
 7 <style type="text/css">@import url("<c:url value="/css/main.css"/>");</style>
 8 </head>
 9 <body>
10 
11 <div id="global">
12 <form:form commandName="employee" action="employee_save" method="post">
13     <fieldset>
14         <legend>Add an employee</legend>
15         <p>
16             <label for="firstName">First Name: </label>
17             <form:input path="firstName" tabindex="1"/>
18         </p>
19         <p>
20             <label for="lastName">First Name: </label>
21             <form:input path="lastName" tabindex="2"/>
22         </p>
23         <p>
24             <form:errors path="birthDate" cssClass="error"/>
25         </p>
26         <p>
27             <label for="birthDate">Date Of Birth: </label>
28             <form:input path="birthDate" tabindex="3" />
29         </p>
30         <p id="buttons">
31             <input id="reset" type="reset" tabindex="4">
32             <input id="submit" type="submit" tabindex="5" 
33                 value="Add Employee">
34         </p>
35     </fieldset>
36 </form:form>
37 </div>
38 </body>
39 </html>

2.Formatter

Formatter也是将一种类型转换成另一种类型

但Formatter源类型必须是一个String，而Converter则适用于任意的源类型

为了创建Formmatter要编写一个org.springframework.format.Formatter接口的java类

public interface Formatter<T>

这里T表示输入字符串要转换的目标类型

T parse(String text,java.util.Locale.locale);

String print(T object,java.util.Locale.locale);

 1 package app06b.formatter;
 2 
 3 import java.text.ParseException;
 4 import java.text.SimpleDateFormat;
 5 import java.util.Date;
 6 import java.util.Locale;
 7 
 8 import org.springframework.format.Formatter;
 9 
10 public class DateFormatter implements Formatter<Date> {
11 
12     private String datePattern;
13     private SimpleDateFormat dateFormat;
14 
15     public DateFormatter(String datePattern) {
16         System.out.println("DateFormatter()5b========");
17         this.datePattern = datePattern;
18         dateFormat = new SimpleDateFormat(datePattern);
19         dateFormat.setLenient(false);
20     }
21 
22     @Override
23     public String print(Date date, Locale locale) {
24         return dateFormat.format(date);
25     }
26 
27     @Override
28     public Date parse(String s, Locale locale) throws ParseException {
29         try {
30             return dateFormat.parse(s);
31         } catch (ParseException e) {
32             // the error message will be displayed when using <form:errors>
33             throw new IllegalArgumentException(
34                     "invalid date format. Please use this pattern""
35                             + datePattern + """);
36         }
37     }
38 }

为了在String MVC应用程序中使用Formmatter，需要利用conversionService bean

进行注册。

bean的类名称必须为org.springframework.format.support.FormattingConversionServiceFactoryBean.

还需要给Formatter添加一个<context:component-scan base-package="app06b.formatter" />

 1 <?xml version="1.0" encoding="UTF-8"?>
 2 <beans xmlns="http://www.springframework.org/schema/beans"
 3     xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:p="http://www.springframework.org/schema/p"
 4     xmlns:mvc="http://www.springframework.org/schema/mvc" xmlns:context="http://www.springframework.org/schema/context"
 5     xsi:schemaLocation="
 6         http://www.springframework.org/schema/beans
 7         http://www.springframework.org/schema/beans/spring-beans.xsd
 8         http://www.springframework.org/schema/mvc
 9         http://www.springframework.org/schema/mvc/spring-mvc.xsd     
10         http://www.springframework.org/schema/context
11         http://www.springframework.org/schema/context/spring-context.xsd">
12 
13     <context:component-scan base-package="app06b.controller" />
14     <context:component-scan base-package="app06b.formatter" />
15 
16     <mvc:annotation-driven conversion-service="conversionService" />
17 
18     <mvc:resources mapping="/css/**" location="/css/" />
19     <mvc:resources mapping="/*.html" location="/" />
20 
21     <bean id="viewResolver"
22         class="org.springframework.web.servlet.view.InternalResourceViewResolver">
23         <property name="prefix" value="/WEB-INF/jsp/" />
24         <property name="suffix" value=".jsp" />
25     </bean>
26 
27     <bean id="conversionService"
28         class="org.springframework.format.support.FormattingConversionServiceFactoryBean">
29         <property name="formatters">
30             <set>
31                 <bean class="app06b.formatter.DateFormatter">
32                     <constructor-arg type="java.lang.String" value="MM-dd-yyyy" />
33                 </bean>
34             </set>
35         </property>
36     </bean>
37 
38 </beans>

3.用Registrar注册Formmatter

注册Formmatter的另一个方法是Registrar

 1 public class MyFormmatterRegistrar implements FormatterRegistrar{
 2     
 3    private String datePattern;
 4    public MyFormmatterRegistrar(String datePattern){
 5          this.datePattern = datePattern;
 6     }
 7 
 8    public void registerFormatters(FormatterRegistry resgitry){
 9        resgitry.addFormatter(new DateFormatter(datePattern));      
10    }
11 }

 1 1  1 <?xml version="1.0" encoding="UTF-8"?>
 2  2  2 <beans xmlns="http://www.springframework.org/schema/beans"
 3  3  3     xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:p="http://www.springframework.org/schema/p"
 4  4  4     xmlns:mvc="http://www.springframework.org/schema/mvc" xmlns:context="http://www.springframework.org/schema/context"
 5  5  5     xsi:schemaLocation="
 6  6  6         http://www.springframework.org/schema/beans
 7  7  7         http://www.springframework.org/schema/beans/spring-beans.xsd
 8  8  8         http://www.springframework.org/schema/mvc
 9  9  9         http://www.springframework.org/schema/mvc/spring-mvc.xsd     
10 10 10         http://www.springframework.org/schema/context
11 11 11         http://www.springframework.org/schema/context/spring-context.xsd">
12 12 12 
13 13 13     <context:component-scan base-package="app06b.controller" />
14 14 14     <context:component-scan base-package="app06b.formatter" />
15 15 15 
16 16 16     <mvc:annotation-driven conversion-service="conversionService" />
17 17 17 
18 18 18     <mvc:resources mapping="/css/**" location="/css/" />
19 19 19     <mvc:resources mapping="/*.html" location="/" />
20 20 20 
21 21 21     <bean id="viewResolver"
22 22 22         class="org.springframework.web.servlet.view.InternalResourceViewResolver">
23 23 23         <property name="prefix" value="/WEB-INF/jsp/" />
24 24 24         <property name="suffix" value=".jsp" />
25 25 25     </bean>
26 26 26 
27 27 27     <bean id="conversionService"
28 28 28         class="org.springframework.format.support.FormattingConversionServiceFactoryBean">
29 29 29         <property name="formatterRegistrars">
30 30 30             <set>
31 31 31                 <bean class="app06b.formatter.MyFormatterRegistrar">
32 32 32                     <constructor-arg type="java.lang.String" value="MM-dd-yyyy" />
33 33 33                 </bean>
34 34 34             </set>
35 35 35         </property>
36 36 36     </bean>
37 37 37 
38 38 38 </beans>

选Converter还是Formatter，一般选Formatter，

因为Formmatter是在Web层