spring 转换器和格式化

　　Spring总是试图用默认的语言区域将日期输入绑定到java.util.Date。假如想让Spring使用不同的日期样式，就需要用一个Converter（转换器）或者 Formatter（格式化）来协助Spring完成。

一. Converter

　　利用Converter进行日期的格式化

　　Spring的Converter是一个可以将一种类型转换成另一种类型的对象。例如，用户输入的日期可能有许多种形式，如“December 25,2014”“12/25/2014”“2014-12- 25” ，这些都表示同一个日期。默认情况下，Spring会期待用户输入的日期样式与当前语言区域的日期样式相同。例如，对于美国的用户而言，就是月/日/年格式。如果希望Spring在将输入的日期字符串绑定到Date时，使用不同的日期样式，则需要编写一个Converter，才能将字符串转换成日期。

1. 日期格式化需要的类:org.springframework.core.convert.converter.Converter

需要实现org.springframework.core.convert.converter.Converter的接口

public interface Converter<S, T

例如

package converter;
 
import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.Date;
import org.springframework.core.convert.converter.Converter;
//必须实现 Converter
public class StringToDateConverter implements Converter<String, Date> {
    private String datePattern;
 
    public StringToDateConverter(String datePattern) {
        this.datePattern = datePattern;
        System.out.println("instantiating .... converter with pattern:*" + datePattern);
    }
    // 转换日期格式
     @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 + "\"");
        }
    }
}

2. springmvc-cofing.xml配置

<mvc:annotation-driven conversion-service="conversionService"/>
    <bean id="conversionService"
        class="org.springframework.context.support.ConversionServiceFactoryBean">
        <property name="converters">
            <list>
                <bean class="converter.StringToDateConverter">
                    <constructor-arg type="java.lang.String"
                        value="MM-dd-yyyy" />
                </bean>
            </list>
        </property>
    </bean>

3.controller类

package 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 domain.Employee;
 
@org.springframework.stereotype.Controller
public class EmployeeController {
    private static final Log  logger = LogFactory.getLog(EmployeeController.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());
        }
        // save  employee here
        model.addAttribute("employee",employee);
 
        return "EmployeeDetails";
    }
}

4.view视图

<%@ taglib prefix="form" uri="http://www.springframework.org/ta
gs/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>
<!-- 打印错误 -->
<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>

二. Formatter

　　Formatter就像Converter一样，也是将一种类型转换成另一种类型。但是，Formatter的源类型必须是一个 String，而Converter则适用于任意的源类型。Formatter 更适合Web层，而Converter则可以用在任意层中。为了转换Spring MVC应用程序表单中的用户输入，始终应该选择Formatter，而不是Converter。

1. 为了创建Formatter，要编写一个实现 org.springframework.format.Formatter接口的Java类。下面是这个接口的声明：

public interface Formatter<T >

　　这里的T表示输入字符串要转换的目标类型。该接口有parse和print两个方法，所有实现都必须覆盖：

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

　　parse方法利用指定的Locale将一个String解析成目标类型。print方法与之相反，它是返回目标对象的字符串表示法。

　　例如，app20a应用程序中用一个DateFormatter将 String转换成Date

DateFormatter类

package fomatter;
 
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;
    /* 这里的datepattern 从springmvc-config.xml传入 */
    public DateFormatter(String datePattern) {
        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 + "\"");
        }
    }
}

app20b的Spring配置文件

<?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: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">
 
    <!-- 配置自定义扫描的包 -->
    <context:component-scan
        base-package="controller">
    </context:component-scan>
    <context:component-scan base-package="formatter"/>
    <bean
        class="org.springframework.web.servlet.view.InternalResourceViewResolver">
        <!-- 前缀 和 后缀 -->
        <property name="prefix" value="/WEB-INF/jsp/" />
        <property name="suffix" value=".jsp" />
    </bean>
 
    <!-- 转换器 -->
    <mvc:annotation-driven conversion-service="conversionService" />
 
    <bean id="conversionService"
        class="org.springframework.format.support.FormattingConversionServiceFactoryBean">
        <property name="formatters">
            <set>
                <bean class="fomatter.DateFormatter">
                    <constructor-arg type="java.lang.String"
                        value="MM-dd-yyyy" />
                </bean>
            </set>
        </property>
    </bean>
</beans>

EmployeeController类

package 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 domain.Employee;
 
@org.springframework.stereotype.Controller
public class EmployeeController {
    private static final Log  logger = LogFactory.getLog(EmployeeController.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());
        }
        // save  employee here
        model.addAttribute("employee",employee);
 
        return "EmployeeDetails";
    }
}

EmployeeForm.jsp页面

<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<%@ 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 modelAttribute="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>

三. 用Registrar注册Formatter

　　注册Formatter的另一种方法是使用Registrar。例如，以下app20b就是注册DateFormatter的一个例子

MyFormatterRegistrar类

package formatter;
 
import org.springframework.format.FormatterRegistrar;
import org.springframework.format.FormatterRegistry;
 
public class MyFormatterRegistrar implements FormatterRegistrar {
    private String datePattern;
 
    public MyFormatterRegistrar(String datePattern) {
        this.datePattern = datePattern;
    }
 
    @Override
    public void registerFormatters(FormatterRegistry registry) {
        registry.addFormatter(new DateFormatter(datePattern));
// register more formatters here
    }
}

　　有了Registrar，就不需要在Spring MVC配置文件中注册任何Formatter了，只在Spring配置文件中注册 Registrar

springmvc-config配置

<?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: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">
 
    <!-- 配置自定义扫描的包 -->
    <context:component-scan
        base-package="controller">
    </context:component-scan>
    <context:component-scan base-package="formatter" />
    <bean
        class="org.springframework.web.servlet.view.InternalResourceViewResolver">
        <!-- 前缀 和 后缀 -->
        <property name="prefix" value="/WEB-INF/jsp/" />
        <property name="suffix" value=".jsp" />
    </bean>
 
    <!-- 转换器 -->
    <mvc:annotation-driven
        conversion-service="conversionService" />
 
    <bean id="conversionService"
        class="org.springframework.format.support.FormattingConversionServiceFactoryBean">
        <property name="formatterRegistrars">
            <set>
                <bean class="formatter.MyFormatterRegistrar">
                    <constructor-arg type="java.lang.String"
                        value="MM-dd-yyyy" />
                </bean>
            </set>
        </property>
    </bean>
 
</beans>

四. 选择Converter，还是 Formatter

　　Converter是一般工具，可以将一种类型转换成另一种类型。例如，将String转换成Date，或者将Long转换成Date。Converter既可以用在Web层，也可以用在其他层中

　　将String转换成Date，但它不能将Long转换成 Date。因此，Formatter适用于Web层。为此，在Spring MVC应用程序中，选择Formatter比选择Converter更合适。