杰克逊：覆盖原始类型的反序列化？

本文介绍了杰克逊：覆盖原始类型的反序列化？的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！ 问题描述

我们需要从遗留服务器处理一些损坏的JSON，错误地将 null 值编码为文字null输出中的字符串。

We need to process some broken JSON from a legacy server here that wrongly encodes null values as literal "null" strings in its output.

我已经发现我可能想要覆盖 github/FasterXML/jackson-core/blob/master/src /main/java/com/fasterxml/jackson/core/base/ParserMinimalBase.java#L368 来修复这个，但这似乎在杰克逊内部如此深刻，我宁愿采取不同的方式。是否有替代方法，例如使用 ObjectMapper 为 String.class 添加自定义反序列化器，或者我丢失了？

I already found that I probably want to override github/FasterXML/jackson-core/blob/master/src/main/java/com/fasterxml/jackson/core/base/ParserMinimalBase.java#L368 to "fix" this, but this seems to be so deep inside Jackson that I'd rather do it differently. Are there alternatives, for example by using the ObjectMapper to add a custom deserializer for the String.class or am I lost?

推荐答案

好的，它通过覆盖标准字符串反序列化器来工作。不幸的是我不得不复制完整的实现，因为 org / codehaus / jackson / map / deser / std / StringDeserializer.java 是最终的，无法扩展。

Ok, it worked by overriding the standard String deserializer. Unfortunately I had to copy the complete implementation over because org/codehaus/jackson/map/deser/std/StringDeserializer.java is final and cannot be extended.

public class FixesModule extends SimpleModule { public FixesModule() { super(); addDeserializer(String.class, new CustomStringDeserializer()); } }

和

public class CustomStringDeserializer extends StdScalarDeserializer { private static final String NULL_STRING = "null"; public CustomStringDeserializer() { super(String.class); } @Override public String deserialize(JsonParser jp, DeserializationContext ctxt) throws IOException, JsonProcessingException { JsonToken curr = jp.getCurrentToken(); // Usually should just get string value: if (curr == JsonToken.VALUE_STRING) { // BEGIN NULL_STRING fix if (NULL_STRING.equals(jp.getText())) { return null; } // END NULL_STRING fix return jp.getText(); } // [JACKSON-330]: need to gracefully handle byte[] data, as base64 if (curr == JsonToken.VALUE_EMBEDDED_OBJECT) { Object ob = jp.getEmbeddedObject(); if (ob == null) { return null; } if (ob instanceof byte[]) { return Base64Variants.getDefaultVariant().encode((byte[]) ob, false); } // otherwise, try conversion using toString()... return ob.toString(); } // Can deserialize any scalar value, but not markers if (curr.isScalarValue()) { return jp.getText(); } throw ctxt.mappingException(_valueClass, curr); } // 1.6: since we can never have type info ("natural type"; String, Boolean, // Integer, Double): // (is it an error to even call this version?) @Override public String deserializeWithType(JsonParser jp, DeserializationContext ctxt, TypeDeserializer typeDeserializer) throws IOException, JsonProcessingException { return deserialize(jp, ctxt); } }