在GSON中期望字符串时如何处理布尔值? [英] How to handle a Boolean when expecting a String in GSON?

问题描述

我目前正在使用第三方REST API进行开发.我正在为API返回的JSON对象创建对象.我正在关注他们的文档，其中说某些变量将是字符串.有时，当没有String时，它将返回False.有时我期待一个URL，但我得到False.

I am currently developing with a 3rd party REST API. I am creating objects for their JSON objects being returned by the API. I am following their documentation where it says certain variables will be Strings. Sometimes when there is no String, it will return False. Sometimes I'm expecting a URL and I get False.

我该如何处理?

这是有问题的API， https://developers.cannabisreports.com/docs/

This is the API in question https://developers.cannabisreports.com/docs/

应变对象示例: https://ghostbin.com/paste/kgeau 在应变对象"中，执行搜索时出现异常.搜索的某些结果在注释掉的代码位中使用布尔值而不是字符串/url.

Strain Object EXAMPLE: https://ghostbin.com/paste/kgeau In the Strain Object, I get an exception when performing a search. Some of the results of the search have booleans instead of strings/url in the bits of code that are commented out.

有时候我明白了

"genetics": {
            "names": false,
            "ucpc": false,
            "link": false
        }

有时候我可以得到这个

"genetics": {
            "names": "Blueberry x Haze",
            "ucpc": "W74AFGH22Z000000000000000 x 9XVU7WJQCD000000000000000",
            "link": "https:\/\/www.cannabisreports.com\/api\/v1.0\/strains\/9XVU7PTG2P000000000000000\/genetics"
        }

推荐答案

当您遇到一个设计得不太好的API的麻烦时，Gson在反序列化由该API生成的JSON文档时会为您提供一些灵活性.尽管您有许多解决此问题的方法(例如JsonDeserializer等)，但您大多数还是喜欢面对我似乎遇到过的 false-as-null 问题已经看到这里了.您可以通过标记错误"字段来帮助Gson:

When you're in trouble with not a very well designed API, Gson gives you some flexibility while deserializing JSON documents produced by such an API. Despite you have numerous ways to work around this issue (like JsonDeserializer, etc), you mostly like are faced with the false-as-null issue I seem to have seen here already. You can help Gson by marking "wrong" fields:

final class Envelope {

    final Genetics genetics = null;

    @Override
    public String toString() {
        return MoreObjects.toStringHelper(this)
                .add("genetics", genetics)
                .toString();
    }

}

final class Genetics {

    @JsonAdapter(FalseAsNullTypeAdapterFactory.class)
    final String names = null;

    @JsonAdapter(FalseAsNullTypeAdapterFactory.class)
    final String ucpc = null;

    @JsonAdapter(FalseAsNullTypeAdapterFactory.class)
    final URL link = null;

    @Override
    public String toString() {
        return MoreObjects.toStringHelper(this)
                .add("names", names)
                .add("ucpc", ucpc)
                .add("link", link)
                .toString();
    }

}

这是类型适配器工厂的实现方式:

And this is how the type adapter factory implemented:

final class FalseAsNullTypeAdapterFactory
        implements TypeAdapterFactory {

    // No worries, Gson will instantiate it itself
    private FalseAsNullTypeAdapterFactory() {
    }

    @Override
    public <T> TypeAdapter<T> create(final Gson gson, final TypeToken<T> typeToken) {
        final TypeAdapter<T> delegateAdapter = gson.getAdapter(typeToken);
        return new TypeAdapter<T>() {
            @Override
            public void write(final JsonWriter out, final T value)
                    throws IOException {
                delegateAdapter.write(out, value);
            }

            @Override
            public T read(final JsonReader in)
                    throws IOException {
                // If the next token is a boolean
                if ( in.peek() == JsonToken.BOOLEAN ) {
                    // and it's true
                    if ( in.nextBoolean() ) {
                        // then just report an unexpected `true` literal
                        throw new MalformedJsonException("Expected a null value indicator as `false`. " + in);
                    }
                    // and it's false, then we assume it's a null
                    return null;
                }
                // Otherwise read the whole value as a usual
                return delegateAdapter.read(in);
            }
        };
    }

}

反序列化问题中提供的JSON文档后，toString -ed映射可能会产生以下内容:

Once you deserialize the JSON documents you provided in the question, a toString-ed mapping might produce something like this:

Envelope{genetics=Genetics{names=null, ucpc=null, link=null}}  
Envelope{genetics=Genetics{names=Blueberry x Haze, ucpc=W74AFGH22Z000000000000000 x 9XVU7WJQCD000000000000000, link=https://www.cannabisreports.com/api/v1.0/strains/9XVU7PTG2P000000000000000/genetics}}  

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