12_property_editor.md

#Property Editor

在设置一个对象类型的属性时：

1. 使用 ref 引用已经存在的对象
2. 使用 bean 标签创建一个匿名对象
3. 还有一种方式是给 value 赋值一个字符串，Spring 自动的把这个字符串转换为对象

第三种方式的实现需要以下几步：

1. 需要提供一个把 String 转换为对象的类，称之为自定义编辑器（CustomEditor）
2. 然后把这个自定义编辑器注册到 Spring
3. 使用字符串配置对象属性

下面就以为 Address 实现一个自定义编辑器 AddressEditor 为例，介绍具体的实现细节。

1. User

package com.jiangge.beans;

public class User {
    private int id;
    private String username;
    private String password;
    private Address address;
    
    // 省略 setter and getter
}

2. Address

package com.jiangge.beans;

public class Address {
    private int id;
    private String country;
    private String province;
    private String street;
    
    // 省略 setter and getter
}

##3. AddressEditor

自定义编辑器需要实现 java.beans.PropertyEditor 接口，java.beans.PropertyEditorSupport 提供了 PropertyEditor 的默认实现，我们只需要继承 PropertyEditorSupport 并实现setAsText() 方法就可以了。

package com.jiangge.beans.editor;

import com.jiangge.beans.Address;
import java.beans.PropertyEditorSupport;

public class AddressEditor extends PropertyEditorSupport {
    /**
     * 把字符串转换为 Address 的对象。
     *
     * @param text 格式为 id|country|province|street
     * @throws IllegalArgumentException
     */
    @Override
    public void setAsText(String text) throws IllegalArgumentException {
        String[] tokens = text.split("\\|");

        Address address = new Address();
        address.setId(Integer.parseInt(tokens[0]));
        address.setCountry(tokens[1]);
        address.setProvince(tokens[2]);
        address.setStreet(tokens[3]);

        setValue(address);
    }
}

4. spring-beans.xml 里注册自定义编辑器

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

    <!--注册自定义的编辑器-->
    <bean class="org.springframework.beans.factory.config.CustomEditorConfigurer">
        <property name="customEditors">
            <map>
                <!--Key 是要生成对象的类名，Value 是 Editor 的类名-->
                <entry key="com.jiangge.beans.Address" value="com.jiangge.beans.editor.AddressEditor"/>
            </map>
        </property>
    </bean>
    ...
</beans>

5. 使用字符串配置 Address 对象属性

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

    <!--注册自定义的 PropertyEditor-->
    <bean class="org.springframework.beans.factory.config.CustomEditorConfigurer">
        <property name="customEditors">
            <map>
                <!--Key 是要生成对象的类名，Value 是 Editor 的类名-->
                <entry key="com.jiangge.beans.Address" value="com.jiangge.beans.editor.AddressEditor"/>
            </map>
        </property>
    </bean>

    <bean id="user" class="com.jiangge.beans.User">
        <property name="username" value="Alice"/>
        <property name="password" value="Passw0rd"/>
        
        <!--Spring 会把字符串 "2|China|BeiJing|WangJin" 自动的转换为 Address 的对象-->
        <property name="address" value="2|China|BeiJing|WangJin"/>
    </bean>
</beans>

6. 测试

import com.jiangge.beans.User;
import com.jiangge.util.CommonUtils;
import com.jiangge.beans.editor.AddressEditor;
import org.junit.BeforeClass;
import org.junit.Test;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

public class AddressEditorTest {
    private static ApplicationContext context;

    @BeforeClass
    public static void setup() {
        context = new ClassPathXmlApplicationContext("spring-beans.xml");
    }

    @Test
    public void test() {
        AddressEditor editor = new AddressEditor();
        editor.setAsText("2|China|BeiJing|WangJin");
        CommonUtils.output(editor.getValue());
    }

    @Test
    public void testAddressEditor() {
        User user = context.getBean("user", User.class);
        CommonUtils.output(user);
    }
}

输出

{
    "id" : 2,
    "country" : "China",
    "province" : "BeiJing",
    "street" : "WangJin"
}
{
    "id" : 0,
    "username" : "Alice",
    "password" : "Passw0rd",
    "address" : {
        "id" : 2,
        "country" : "China",
        "province" : "BeiJing",
        "street" : "WangJin"
    }
}