simpleframework，将空元素反序列化为空字符串而不是null [英] simpleframework, deserializing an empty element to an empty string instead of null

问题描述

我在项目中使用simpleframework（http://simple.sourceforge.net/）来进行序列化/反序列化需求，但是在处理空/时它没有按预期工作（好吧，至少不是我期望的） null字符串值。

I use simpleframework (http://simple.sourceforge.net/) in a project for my serializing / deserializing needs, but it doesn't work as expected (well, atleast not how I expect) when dealing with empty / null String values.

如果我使用空字符串值序列化对象，它将显示为空的xml元素。

If I serialize an object with an empty String value, it will show as an empty xml element.

所以这个

MyObject object = new MyObject（）;

object.setAttribute（）; // attribute is String

将序列化为

< object>

< attribute>< / attribute>

< / object>

但反序列化empty属性将以null结尾，而不是空字符串。

But deserializing that empty attribute will end up as null, instead of an empty String.

我认为它应该是一个空字符串而不是null，我完全疯了吗？我怎么能以我想要的方式使它工作？

Am I completely bonkers for thinking that it should be an empty String instead of null? And how on earth can I make it to work in the way I wan't?

哦，如果我使用null属性序列化对象，它将最终显示
< object />
正如人们所料。

Oh, and if I serialize the object with a null attribute it will end up showing <object/> as one might expect.

编辑：

添加了一个我目前正在运行的简单测试用程序

Added a simple testcase I'm currenty running

@Test  
public void testDeserialization() throws Exception {  
    StringWriter writer = new StringWriter();  
    MyDTO dto = new MyDTO();  
    dto.setAttribute("");  

    Serializer serializer = new Persister();  
    serializer.write(dto, writer);  

    System.out.println(writer.getBuffer().toString());

    MyDTO read = serializer.read(MyDTO.class, writer.getBuffer().toString(),true);
    assertNotNull(read.getAttribute());  
}


@Root  
public class MyDTO {  
    @Element(required = false)  
    private String attribute;  

    public String getAttribute() {  
        return attribute;  
    }  

    public void setAttribute(String attribute) {  
        this.attribute = attribute;  
    }  
}  

编辑，修正：

由于某种原因，当一个空字符串传递给它时，InputNode值为null。我通过创建自定义Converter for String解决了这个问题。

For some reason the InputNode value is null when an empty string is passed to it. I resolved the problem by creating a custom Converter for String.

new Converter<String>() {

    @Override
    public String read(InputNode node) throws Exception {
        if(node.getValue() == null) {
            return "";
        }
        return node.getValue();
    }

    @Override
    public void write(OutputNode node, String value) throws Exception {
        node.setValue(value);
    }

});

推荐答案

回答完整性

使用转换注释注释元素，并将转换器类作为参数
@Convert（SimpleXMLStringConverter.class）

Annotate your element with the convert annotation and give it a converter class as a parameter @Convert(SimpleXMLStringConverter.class)

创建转换器类，将字符串从null转换为空字符串

Create the converter class that does string conversion from null to empty string

public class SimpleXMLStringConverter implements Converter<String> {


    @Override
    public String read(InputNode node) throws Exception {
        String value = node.getValue();
        if(value == null) {
            value = "";
        }
        return value;
    } 

    @Override
    public void write(OutputNode node, String value) throws Exception {
        node.setValue(value);
    }

}

不要去将 new AnnotationStrategy（）添加到您的信息中。

And don't for get to add new AnnotationStrategy() to your persister.

这篇关于simpleframework，将空元素反序列化为空字符串而不是null的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！