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);

package app06a.converter;

import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.Date;

import org.springframework.core.convert.converter.Converter;

public class StringToDateConverter implements Converter<String, Date> {

    private String datePattern;

    public StringToDateConverter(String datePattern) {
        this.datePattern = datePattern;
    }

    @Override
    public Date convert(String s) {
        try {
            SimpleDateFormat dateFormat = new SimpleDateFormat(datePattern);
            dateFormat.setLenient(false);
            return dateFormat.parse(s);
        } catch (ParseException e) {
            // the error message will be displayed when using <form:errors>
            throw new IllegalArgumentException(
                    "invalid date format. Please use this pattern""
                            + datePattern + """);
        }
    }
}

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

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xmlns:p="http://www.springframework.org/schema/p"
    xmlns:mvc="http://www.springframework.org/schema/mvc"
    xmlns:context="http://www.springframework.org/schema/context"
    xsi:schemaLocation="
        http://www.springframework.org/schema/beans
        http://www.springframework.org/schema/beans/spring-beans.xsd
        http://www.springframework.org/schema/mvc
        http://www.springframework.org/schema/mvc/spring-mvc.xsd     
        http://www.springframework.org/schema/context
        http://www.springframework.org/schema/context/spring-context.xsd">
        
    <context:component-scan base-package="app06a.controller"/>
     
17     <mvc:annotation-driven conversion-service="conversionService"/>
    <mvc:resources mapping="/css/**" location="/css/"/>
    <mvc:resources mapping="/*.html" location="/"/>
    
    <bean id="viewResolver" class="org.springframework.web.servlet.view.InternalResourceViewResolver">
        <property name="prefix" value="/WEB-INF/jsp/"/>
        <property name="suffix" value=".jsp"/>
    </bean>
    
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>
</beans>

Employee类

package app06a.domain;

import java.io.Serializable;
import java.util.Date;

public class Employee implements Serializable {
    private static final long serialVersionUID = -908L;

    private long id;
    private String firstName;
    private String lastName;
    private Date birthDate;
    private int salaryLevel;

    public long getId() {
        return id;
    }

    public void setId(long id) {
        this.id = id;
    }

    public String getFirstName() {
        return firstName;
    }

    public void setFirstName(String firstName) {
        this.firstName = firstName;
    }

    public String getLastName() {
        return lastName;
    }

    public void setLastName(String lastName) {
        this.lastName = lastName;
    }

    public Date getBirthDate() {
        return birthDate;
    }

    public void setBirthDate(Date birthDate) {
        this.birthDate = birthDate;
    }

    public int getSalaryLevel() {
        return salaryLevel;
    }

    public void setSalaryLevel(int salaryLevel) {
        this.salaryLevel = salaryLevel;
    }

}

Controller

有了StringToDateConverter converter，就不需要劳驾

controller类将字符串转换成日期了

package app06a.controller;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.springframework.ui.Model;
import org.springframework.validation.BindingResult;
import org.springframework.validation.FieldError;
import org.springframework.web.bind.annotation.ModelAttribute;
import org.springframework.web.bind.annotation.RequestMapping;

import app06a.domain.Employee;

@org.springframework.stereotype.Controller

public class EmployeeController {
    
    private static final Log logger = LogFactory.getLog(ProductController.class);
    
    @RequestMapping(value="employee_input")
    public String inputEmployee(Model model) {
        model.addAttribute(new Employee());
        return "EmployeeForm";
    }

    @RequestMapping(value="employee_save")
    public String saveEmployee(@ModelAttribute Employee employee, BindingResult bindingResult,
            Model model) {
        if (bindingResult.hasErrors()) {
            FieldError fieldError = bindingResult.getFieldError();
            logger.info("Code:" + fieldError.getCode() 
                    + ", field:" + fieldError.getField());
            return "EmployeeForm";
        }
        
        // save employee here
        
        model.addAttribute("employee", employee);
        return "EmployeeDetails";
    }
}

<%@ taglib prefix="form" uri="http://www.springframework.org/tags/form" %>
<%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c" %>
<!DOCTYPE HTML>
<html>
<head>
<title>Add Employee Form</title>
<style type="text/css">@import url("<c:url value="/css/main.css"/>");</style>
</head>
<body>

<div id="global">
<form:form commandName="employee" action="employee_save" method="post">
    <fieldset>
        <legend>Add an employee</legend>
        <p>
            <label for="firstName">First Name: </label>
            <form:input path="firstName" tabindex="1"/>
        </p>
        <p>
            <label for="lastName">First Name: </label>
            <form:input path="lastName" tabindex="2"/>
        </p>
        <p>
            <form:errors path="birthDate" cssClass="error"/>
        </p>
        <p>
            <label for="birthDate">Date Of Birth: </label>
            <form:input path="birthDate" tabindex="3" />
        </p>
        <p id="buttons">
            <input id="reset" type="reset" tabindex="4">
            <input id="submit" type="submit" tabindex="5" 
                value="Add Employee">
        </p>
    </fieldset>
</form:form>
</div>
</body>
</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);

package app06b.formatter;

import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.Date;
import java.util.Locale;

import org.springframework.format.Formatter;

public class DateFormatter implements Formatter<Date> {

    private String datePattern;
    private SimpleDateFormat dateFormat;

    public DateFormatter(String datePattern) {
        System.out.println("DateFormatter()5b========");
        this.datePattern = datePattern;
        dateFormat = new SimpleDateFormat(datePattern);
        dateFormat.setLenient(false);
    }

    @Override
    public String print(Date date, Locale locale) {
        return dateFormat.format(date);
    }

    @Override
    public Date parse(String s, Locale locale) throws ParseException {
        try {
            return dateFormat.parse(s);
        } catch (ParseException e) {
            // the error message will be displayed when using <form:errors>
            throw new IllegalArgumentException(
                    "invalid date format. Please use this pattern""
                            + datePattern + """);
        }
    }
}

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" />

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:p="http://www.springframework.org/schema/p"
    xmlns:mvc="http://www.springframework.org/schema/mvc" xmlns:context="http://www.springframework.org/schema/context"
    xsi:schemaLocation="
        http://www.springframework.org/schema/beans
        http://www.springframework.org/schema/beans/spring-beans.xsd
        http://www.springframework.org/schema/mvc
        http://www.springframework.org/schema/mvc/spring-mvc.xsd     
        http://www.springframework.org/schema/context
        http://www.springframework.org/schema/context/spring-context.xsd">

    <context:component-scan base-package="app06b.controller" />
    <context:component-scan base-package="app06b.formatter" />

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

    <mvc:resources mapping="/css/**" location="/css/" />
    <mvc:resources mapping="/*.html" location="/" />

    <bean id="viewResolver"
        class="org.springframework.web.servlet.view.InternalResourceViewResolver">
        <property name="prefix" value="/WEB-INF/jsp/" />
        <property name="suffix" value=".jsp" />
    </bean>

    <bean id="conversionService"
        class="org.springframework.format.support.FormattingConversionServiceFactoryBean">
        <property name="formatters">
            <set>
                <bean class="app06b.formatter.DateFormatter">
                    <constructor-arg type="java.lang.String" value="MM-dd-yyyy" />
                </bean>
            </set>
        </property>
    </bean>

</beans>

3.用Registrar注册Formmatter

注册Formmatter的另一个方法是Registrar

public class MyFormmatterRegistrar implements FormatterRegistrar{
    
   private String datePattern;
   public MyFormmatterRegistrar(String datePattern){
         this.datePattern = datePattern;
    }

   public void registerFormatters(FormatterRegistry resgitry){
       resgitry.addFormatter(new DateFormatter(datePattern));      
   }
}

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

选Converter还是Formatter，一般选Formatter，

因为Formmatter是在Web层