<spring:transform> 標籤

Spring的<spring:transform>標籤必須位於<spring:bind>標籤之中，搭配 PropertyEditor使用的話，您可以將Command的屬性值轉換為您所要的字串格式。

舉個實際的例子來說，假設您的Command中儲存了星期的數字表示，例如星期一使用"1"表示，星期二使用"2"表示…星期日使用"0" 表示，然而您希望在填寫表示時，您可以在表單上顯示的是"MON"、"THU"、"WED"等字樣，您希望使用程式自動幫您完成轉換。

可以先設計一個WeekForm類別，收集請求參數值"0"到"6"：

WeekForm.java

package onlyfun.caterpillar;

public class WeekForm {
    private String weekNumber;
    
    public void setWeekNumber(String weekNumber) {
        this.weekNumber = weekNumber;
    }

    public String getWeekNumber() {
        return weekNumber;
    }
}

weekNumber儲存的是"1"、"2"、"3"之類的請求參數值，接著您可以設計一個WeekPropertyEditor類別來轉換這些參數值為"MON"、"TUE"到"SUN"：

WeekPropertyEditor.java

package onlyfun.caterpillar;

import java.beans.PropertyEditorSupport;

public class WeekPropertyEditor extends PropertyEditorSupport {    
    public void setAsText(String text) {
        if("MON".equals(text)) {
            setValue("1");
        }
        else if("TUE".equals(text)) {
            setValue("2");
        }
        else if("WED".equals(text)) {
            setValue("3");
        }
        else if("THU".equals(text)) {
            setValue("4");
        }
        else if("FRI".equals(text)) {
            setValue("5");
        }
        else if("SAT".equals(text)) {
            setValue("6");
        }        
        else if("SUN".equals(text)) {
            setValue("0");
        }        
        else {
            setValue("");
        }
    }
    
    public String getAsText() {
        if(this.getValue() != null 
                && !(this.getValue() instanceof String)) {
            return "";
        }
        
        String text = (String) this.getValue();
        
        if("1".equals(text)) {
            return "MON";
        }
        else if("2".equals(text)) {
            return "TUE";
        }
        else if("3".equals(text)) {
            return "WED";
        }
        else if("4".equals(text)) {
            return "THU";
        }
        else if("5".equals(text)) {
            return "FRI";
        }
        else if("6".equals(text)) {
            return "SAT";
        }
        else if("0".equals(text)) {
            return "SUN";
        }
        else {
            return text;
        }
    }
}

您在設計Controller時，必須重新定義initBinder()方法以註冊這個自訂的PropertyEditor，例如：

WeekFormController.java

package onlyfun.caterpillar;

import org.springframework.web.servlet.
                                mvc.SimpleFormController; 
import org.springframework.web.servlet.*;
import java.util.*;
import javax.servlet.http.HttpServletRequest;
import org.springframework.validation.BindException;
import org.springframework.web.
                            bind.ServletRequestDataBinder;

public class WeekFormController extends SimpleFormController {
    private Map refData;
    
    public WeekFormController() {
        setCommandClass(WeekForm.class); 
        
        refData = new HashMap();
        
        List list = new ArrayList();
        for(int i = 0; i < 7; i++) {
            list.add(String.valueOf(i));
        }
        
        refData.put("weekNumbers", list);        
    }

    protected ModelAndView onSubmit(Object command,
                   BindException errors) throws Exception { 
       WeekForm form = (WeekForm) command; 
        
       if(form.getWeekNumber() == null) {
          return new ModelAndView(this.getFormView()); 
       } 
       else { 
          return new ModelAndView(
                  this.getSuccessView(), errors.getModel()); 
       } 
    }

    protected Map referenceData(
           HttpServletRequest request) throws Exception { 
        return refData;
    }
    
    protected void initBinder(HttpServletRequest request, 
              ServletRequestDataBinder binder) throws Exception {
        super.initBinder(request, binder); 
        binder.registerCustomEditor(
                String.class, new WeekPropertyEditor());
    }
}

在建構WeekFormController時，會預先準備好"0"到"6"的字串值，referenceData()方法會返回包括這些字串值的Map 物件，以在頁面上加以顯示，由於在initBinder()中註冊了自訂的WeekPropertyEditor，再配合<spring: transform>標籤，就可以在頁面上顯示"SUN"、"MON"等文字，頁面form.jsp的設計如下所示，當中搭配了JSTL來協助頁面邏輯的撰寫：

form.jsp

<%@page contentType="text/html"%>
<%@page pageEncoding="UTF-8"%>
<%@taglib prefix="c" 
                 uri="http://java.sun.com/jsp/jstl/core"%>
<%@taglib prefix="spring" 
                 uri="http://www.springframework.org/tags"%>

<html>
    <head> 
        <meta http-equiv="Content-Type" 
              content="text/html; charset=UTF-8">
        <title>JSP Page</title>
    </head>
    <body>
    <spring:bind path="command.*">
        <font color="red">
            <c:out value="\${status.errorMessage}"/>
        </font>
    </spring:bind>
    
    <form name="weekForm" 
          action="/TransFormTagDemo/weekForm.do" 
          method="POST">
        <spring:bind path="command.weekNumber">
            <select name="weekNumber">
                <c:forEach var="weekNumber" 
                                             items="\${weekNumbers}" >
                    <spring:transform value="\${weekNumber}" 
                                          var="weekName"/>
                    <c:choose>
                    
                    <c:when test="\${status.value == weekName}">
                    <option value="<c:out value="\${weekName}"/>" 
                                        selected>
                    </c:when>
                    <c:otherwise> 
                    <option value="<c:out value="\${weekName}"/>">
                    </c:otherwise>
                    
                    </c:choose>
                        <c:out value="\${weekName}"/>
                    </option>     
                </c:forEach>
            </select>
        </spring:bind>
        <input type="submit" value="Submit"/>  
    </form>
    </body>
</html>

Bean定義檔如下撰寫，由於使用了JSTL，所以在InternalResourceViewResolver的"viewClass"的設定上可以使用JstlView類別：

mvc-config.xml

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE beans PUBLIC "-//SPRING/DTD BEAN/EN" 
 "http://www.springframework.org/dtd/spring-beans.dtd"> 

<beans>   
    <bean id="viewResolver"
          class="org.springframework.web.servlet.
                   → view.InternalResourceViewResolver">    
        <property name="viewClass">          
            <value>
                org.springframework.web.servlet.view.JstlView
            </value>
        </property>
        <property name="prefix">
            <value>/WEB-INF/jsp/</value>
        </property>
        <property name="suffix">
            <value>.jsp</value>
        </property>
    </bean>
    
    <bean name="/weekForm.do" 
          class="onlyfun.caterpillar.WeekFormController"> 
        <property name="formView"> 
            <value>form</value> 
        </property>           
        <property name="successView"> 
            <value>success</value> 
        </property>        
    </bean>
</beans>