Question

我有一个类似的类：

class TestJsonClass {
    private String propertyA;
    private String propertyB;
    private String propertyC;
}

现在在运行时我希望为每个属性提供不同的属性名称，而不是使用@JsonProperty（“sample”）的静态属性

我如何做到这一点？我正在使用Jackson库广告Spring MVC

提前致谢...

Answer 1

您可以为此目的使用Modules。这是解决您问题的最简单方法。这是一个例子：

一个简单的类，可以为每个请求提供属性名称映射：

public class PropertyNameMapper {
    // The class for which the mappings need to take place.
    public Class<?> classToFilter;
    // The mappings property names. Key would be the existing property name
    // value would be name you want in the ouput.
    public Map<String, String> nameMappings = Collections.emptyMap();

    public PropertyNameMapper(Class<?> classToFilter, Map<String, String> nameMappings) {
        this.classToFilter = classToFilter;
        this.nameMappings = nameMappings;
    }
}

自定义BeanPropertyWriter，用于指定属性的输出名称。

public class MyBeanPropertyWriter extends BeanPropertyWriter {
    // We would just use the copy-constructor rather than modifying the
    // protected properties. This is more in line with the current design
    // of the BeanSerializerModifier class (according to its documentation).
    protected MyBeanPropertyWriter(BeanPropertyWriter base, String targetName) {
        super(base, new SerializedString(targetName));
    }

}

现在，每次调用一个自定义BeanSerializerModifier，允许您修改序列化属性。

public class MySerializerModifier extends BeanSerializerModifier {

    public List<BeanPropertyWriter> changeProperties(
            SerializationConfig config, BeanDescription beanDesc,
            List<BeanPropertyWriter> beanProperties) {

        List<PropertyNameMapper> propertyMappings = getNameMappingsFromRequest();
        PropertyNameMapper mapping = mappingsForClass(propertyMappings,
                beanDesc.getBeanClass());

        if (mapping == null) {
            return beanProperties;
        }

        List<BeanPropertyWriter> propsToWrite = new ArrayList<BeanPropertyWriter>();
        for (BeanPropertyWriter propWriter : beanProperties) {
            String propName = propWriter.getName();
            String outputName = mapping.nameMappings.get(propName);
            if (outputName != null) {
                BeanPropertyWriter modifiedWriter = new MyBeanPropertyWriter(
                        propWriter, outputName);
                propsToWrite.add(modifiedWriter);
            } else {
                propsToWrite.add(propWriter);
            }
        }
        return propsToWrite;
    }

    private List<PropertyNameMapper> getNameMappingsFromRequest() {
        RequestAttributes requestAttribs = RequestContextHolder
                .getRequestAttributes();
        List<PropertyNameMapper> nameMappings = (List<PropertyNameMapper>) requestAttribs
                .getAttribute("nameMappings",
                        RequestAttributes.SCOPE_REQUEST);
        return nameMappings;
    }

    private PropertyNameMapper mappingsForClass(
            List<PropertyNameMapper> nameMappings, Class<?> beanClass) {
        for (PropertyNameMapper mapping : nameMappings) {
            if (mapping.classToFilter.equals(beanClass)) {
                return mapping;
            }
        }
        return null;
    }
}

现在，您需要自定义Module才能使用上面创建的BeanSerializerModifier自定义输出：

public class MyModule extends Module {

    @Override
    public String getModuleName() {
        return "Test Module";
    }

    @Override
    public void setupModule(SetupContext context) {
        context.addBeanSerializerModifier(new MySerializerModifier());
    }

    @Override
    public Version version() {
        // Modify if you need to.
        return Version.unknownVersion();
    }
}

现在使用ObjectMapper注册此模块。您可以从Spring应用程序上下文中获取Jackson HTTP消息转换器，并获取其对象映射器。

// Figure out a way to get the ObjectMapper.
MappingJackson2HttpMessageConverter converter = ... // get the jackson-mapper;
converter.getObjectMapper().registerModule(new MyModule())

就是这样。这是动态自定义属性序列化的最简单方法。

要使用此功能，请创建List PropertyNameMappers并将其添加为当前请求中的属性（在此示例中名为“nameMappings”）。

这是一个示例，而不是生产就绪代码。您可能需要添加空检查和类似的事情。此外，根据您使用的库版本，可能需要进行一些小的调整。

如果解决方案不适合您，请告诉我您遇到的问题。

Answer 2

您可以将自定义PropertyNamingStrategy注入到反序列化中使用的ObjectMapper中。

只需在运行时将字段设置到PropertyNamingStrategy中，假设您可以将它们映射到默认的JsonPropertyName（例如propertyA，propertyB，propertyC）。

public class MyNamingStrategy extends PropertyNamingStrategy {

    String propertyAName, propertyBName, propertyCName;

    public MyNamingStrategy(String propANm, String propBNm, String propCNm) {
        this.propertyAName = propANm;
        //finish
    }

    @Override
    public String nameForField(MapperConfig<?> config, AnnotatedField field,
            String defaultName) {
        return convert(defaultName);
    }

    @Override
    public String nameForGetterMethod(MapperConfig<?> config,
            AnnotatedMethod method, String defaultName) {
        return convert(defaultName);
    }

    @Override
    public String nameForSetterMethod(MapperConfig<?> config,
            AnnotatedMethod method, String defaultName) {
        return convert(defaultName);
    }

    public String convert(String defaultName ){
        return defaultName.replace("propertyA", propertyAName).replace( //finish
    }

最后，您要创建一个实例并在运行时注入它。 objectMapper.setNamingStrategy（myNamingStrategyInstance））;

有关PropertyNamingStrategy的更多信息，请参阅此Cowtowncoder帖子：

Jackson 1.8: custom property naming strategies

或者此文档：

github.com/FasterXML/jackson-docs/wiki/PropertyNamingStrategy

动态更改Json密钥名称 - 杰克逊

2 个答案: