binding - Spring MVC 绑定(bind)

Question

我有以下命令对象:

public class User {
    private Department department;
    private String firstName;
    private String lastName;
    private String login;
    private String password;
...
}

应该在jsp页面呈现:

<form:input path="lastName" />
<form:input path="department.name"/>
<form:input path="department.description"/>

因此，当我使用空的部门名称和部门描述提交时，Spring 会自动实例化具有空属性的对象部门。 (参见 https://jira.springframework.org/browse/SPR-6032 我会保留 autoGrowNestedPaths=true)

取回 Department object=null 的 User 对象需要做什么？

Answer 1

What is need to do for getting back User object where Department object=null?

如果您正在寻找特定于 Controller 的解决方案，请找到所有空的嵌套参数并将这些参数设置为不允许的字段。

@InitBinder(value="user")
    public void bind(WebDataBinder dataBinder, WebRequest webRequest) {
        List<String> emptyParams = new ArrayList<String>();
        Iterator<String> itr = webRequest.getParameterNames();
        while(itr.hasNext()) {
            String name = itr.next();
            if(name.startsWith("department.")) {
                Object value = webRequest.getParameter(name);
                if("".equals(value)) {
                    emptyParams.add(name);
                }
            }
        }
        if(!emptyParams.isEmpty()) {
            dataBinder.setDisallowedFields(emptyParams.toArray(new String[emptyParams.size()]));
        }
    }

如果您正在寻找通用解决方案，请创建自定义数据绑定(bind)器并删除所有空的嵌套参数。

public class CustomDataBinder extends ServletRequestDataBinder {

    @Override
    protected void doBind(MutablePropertyValues mpvs) {
        PropertyValue[] pvArray = mpvs.getPropertyValues();
        for (PropertyValue pv : pvArray) {
            boolean nestedProperty = PropertyAccessorUtils.isNestedOrIndexedProperty(pv.getName());
            if(nestedProperty && "".equals(pv.getValue())) {
                mpvs.removePropertyValue(pv);
            }
        }
        super.doBind(mpvs);
    }

}

要使用 CustomDataBinder，您必须拥有自定义 HandlerAdapter。

public class StandardAnnotationMethodHandlerAdapter extends AnnotationMethodHandlerAdapter    {
    @Override
    protected ServletRequestDataBinder createBinder(HttpServletRequest request, Object target, String objectName) throws Exception {
    CustomDataBinder dataBinder = new CustomDataBinder (target, objectName);
    return dataBinder;
   }
}