java - 如何在 Spring MVC Web 应用程序中注册格式化程序？

Question

我在绑定(bind)模型属性中的嵌套对象时遇到问题。我有一本书，其中嵌套了类主题，如下所示:

@Entity
@Table(name = "book")
public class Book {

    // Other properties...
    // With all getter setter..
    @ManyToOne
    @JoinColumn(name="subject_id",nullable=false)
    @NotBlank(message = "Please select subject")
    private Subject subject;
    // Getter setter of subject;
}

我还为 Subject 实现了 Formatter 类，如下所示:

@Component
public class SubjectFormatter implements Formatter<Subject>{

    @Autowired
    SubjectService subjectService;

    @Override
    public String print(Subject object, Locale locale) {
        return object.getName();
    }

    @Override
    public Subject parse(String id, Locale locale) throws ParseException {
        return subjectService.getSubject(id);
    }
}

并在 spring 配置中添加格式化程序:

@EnableWebMvc
@Configuration
@PropertySource(value = { "classpath:application.properties" })
@ComponentScan(basePackages = "com.vbera.main")
@EnableJpaRepositories(basePackages = "com.vbera.main")
public class SpringConfiguration extends WebMvcConfigurerAdapter {

    //Other bean definitions...

    @Bean(name="conversionService")
    public FormattingConversionService conversionService() {
        FormattingConversionServiceFactoryBean bean = new FormattingConversionServiceFactoryBean();
        bean.setRegisterDefaultFormatters(false);
        bean.setFormatters(getFormatters());
        return bean.getObject();
    }

    private Set<Formatter> getFormatters() {
        Set<Formatter> converters = new HashSet<Formatter>();
        converters.add(new SubjectFormatter());
        return converters;
    }
}

我仍然在提交时遇到异常:

Failed to convert property value of type java.lang.String to required type com.vbera.main.pojo.Subject for property subject

主题列表呈现的 JSP View :

<form:label path="subject" for="subject">Subject</form:label>
<form:select path="subject" class="form-control input-md">
    <form:option value="">--- Select ---</form:option>
    <form:options items="${subjectList}" itemLabel="name"
        itemValue="id" />
</form:select>

Answer 1

您的 mvc.xml 中有两个部分文件。

1. 添加 bean 转换服务 bean:

<bean id="conversionService"
    class="org.springframework.format.support.FormattingConversionServiceFactoryBean">
   <property name="formatters">
       <set>
           <ref bean="MyFormatter1" />
           <ref bean="MyFormatter2" />
       </set>
   </property>
   <property name="converters">
        <set>
            <ref bean="MyConverter1" />
            <ref bean="MyConverter2" />
        </set>
    </property>
</bean>

1. 在注释驱动的标记中引用此 bean。

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

大多数时候使用 ID 是可以的。但是，在表单中，它会强制 Spring 创建一个具有 null Id 的空对象而不是 null 对象。