From Gossip@caterpillar

Spring Gossip: 使用 PropertyEditor

對於BaseCommandController及其子類別來說，它的Command物件並不一定要接受基本型態或是String型態，您可以撰寫一個實作 java.beans.PropertyEditor的類別，在當中進行轉換，例如將接收到的字串轉換為User類別的實例。

舉個實例來說，假設您的Command物件如下設計：

SomeForm.java

package onlyfun.caterpillar;

public class SomeForm {
    private User user; 
    
    public void setUser(User user) { 
        this.user = user;
    }
    
    public User getUser() { 
        return user;
    }
}

SomeForm為網頁表單的物件代表，而其中出現的User類別如下設計：

User.java

package onlyfun.caterpillar;

public class User {
    private String firstName;
    private String lastName;
    
    public void setFirstName(String firstName) {
        this.firstName = firstName;
    }
    
    public void setLastName(String lastName) {
        this.lastName = lastName;
    }
    
    public String getFirstName() {
        return firstName;
    }
    
    public String getLastName() {
        return lastName;
    }
}

您的Command物件將接收一個自訂型態的User實例，然而從HTTP接收到的參數值是String型態，您可以撰寫一個 UserPropertyEditor類別做轉換，通常直接繼承java.beans.PropertyEditorSupport並重新定義它的 getAsText()及setAsText()方法，例如：

UserPropertyEditor.java

package onlyfun.caterpillar;

import java.beans.PropertyEditorSupport;

public class UserPropertyEditor extends PropertyEditorSupport {
    public String getAsText() {
        Object o = this.getValue();
        
        if(o == null || !(o instanceof User)) {
            return null;
        }
        
        User user = (User) o;       
        String name = user.getFirstName() 
                       + "," + user.getLastName();       
        return name;
    }
    
    public void setAsText(String text) {
        String[] tokens = text.split(",");
        
        User user = new User();
        user.setFirstName(tokens[0]);
        user.setLastName(tokens[1]);
        
        setValue(user);
    }
}

當必須從指定的物件轉換為字串時，會呼叫getAsText()方法，而接收到參數要將之轉換為指定的物件時，會呼叫setAsText()方法，接著來撰寫一個測試的Controller：

SomeFormController.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.web.
                        bind.ServletRequestDataBinder;

public class SomeFormController extends SimpleFormController {
    public SomeFormController() {
        setCommandClass(SomeForm.class);  
    }

    protected ModelAndView onSubmit(
                      Object command) throws Exception { 
       SomeForm form = (SomeForm) command;
       
       Map model = new HashMap();
       model.put("firstName", 
                 form.getUser().getFirstName()); 
       model.put("lastName", 
                 form.getUser().getLastName());
       
       return new ModelAndView(this.getSuccessView(), model);
    }
    
    protected void initBinder(HttpServletRequest request, 
                          ServletRequestDataBinder binder) 
                                           throws Exception {
        super.initBinder(request, binder); 
        binder.registerCustomEditor(
                User.class, new UserPropertyEditor());
    }
}

注意到這邊重新定義了initBinder()方法，並在當中使用ServletRequestDataBinder的registerCustomEditor()方法註冊了自訂的PropertyEditor，來看看定義檔的內容：

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="urlMapping"
          class="org.springframework.web.servlet.
                → handler.SimpleUrlHandlerMapping">
        <property name="mappings">
            <props>
                <prop key="/index.do">
                   indexController
                </prop>
                <prop key="/someForm.do">
                   someFormController
                </prop>
            </props>
        </property>
    </bean> 
    
    <bean id="viewResolver"
          class="org.springframework.web.servlet.
                → view.InternalResourceViewResolver">    
        <property name="prefix">
            <value>/WEB-INF/jsp/</value>
        </property>
        <property name="suffix">
            <value>.jsp</value>
        </property>
    </bean>

    <bean id="indexController"
           class="org.springframework.web.servlet.
                       → mvc.ParameterizableViewController">
        <property name="viewName">
            <value>index</value>
        </property>     
    </bean>    
    
    <bean id="someFormController" 
          class="onlyfun.caterpillar.SomeFormController"> 
        <property name="successView"> 
            <value>hello</value> 
        </property>        
    </bean>
</beans>

現在假設撰寫有一個測試網頁：

index.jsp

<%@page contentType="text/html"%>
<%@page pageEncoding="UTF-8"%>

<html>
    <head>
        <meta http-equiv="Content-Type"
              content="text/html; charset=UTF-8">
        <title>Form</title>
    </head>
    <body>
    <form name="someForm" 
          action="/PropertyEditorDemo/someForm.do" method="POST"> 
        問題一 <input type="text" name="user"/><br> 
        <input type="submit" value="Submit"/>         
    </form> 
    </body>
</html>

在輸入欄位中，指定由user屬性來接受輸入，當資料送出後，會經由PropertyEditor的轉換，假設呈現處理結果的hello.jsp網頁是如下撰寫的：

hello.jsp

<%@page contentType="text/html"%>
<%@page pageEncoding="UTF-8"%>

<html>
    <head>
        <meta http-equiv="Content-Type" 
              content="text/html; charset=UTF-8">
        <title>User Info</title>
    </head>
    <body>
    <h1>${firstName} - ${lastName}</h1>
    </body>
</html>

如果您在index.jsp填入"Justin,Lin"，則結果會顯示"Justin-Lin"。