spring学习笔记

spring的9中messageConverter

org.springframework.web.servlet.mvc.method.annotation.AbstractMessageConverterMethodArgumentResolver

for (HttpMessageConverter<?> converter : this.messageConverters) {
   Class<HttpMessageConverter<?>> converterType = (Class<HttpMessageConverter<?>>) converter.getClass();
   if (converter instanceof GenericHttpMessageConverter) {
      GenericHttpMessageConverter<?> genericConverter = (GenericHttpMessageConverter<?>) converter;
      if (genericConverter.canRead(targetType, contextClass, contentType)) {
         if (logger.isDebugEnabled()) {
            logger.debug("Read [" + targetType + "] as \"" + contentType + "\" with [" + converter + "]");
         }
         if (inputMessage.getBody() != null) {
            inputMessage = getAdvice().beforeBodyRead(inputMessage, parameter, targetType, converterType);
            body = genericConverter.read(targetType, contextClass, inputMessage);
            body = getAdvice().afterBodyRead(body, inputMessage, parameter, targetType, converterType);
         }
         else {
            body = getAdvice().handleEmptyBody(null, inputMessage, parameter, targetType, converterType);
         }
         break;
      }
   }
   else if (targetClass != null) {
      if (converter.canRead(targetClass, contentType)) {
         if (logger.isDebugEnabled()) {
            logger.debug("Read [" + targetType + "] as \"" + contentType + "\" with [" + converter + "]");
         }
         if (inputMessage.getBody() != null) {
            inputMessage = getAdvice().beforeBodyRead(inputMessage, parameter, targetType, converterType);
            body = ((HttpMessageConverter<T>) converter).read(targetClass, inputMessage);
            body = getAdvice().afterBodyRead(body, inputMessage, parameter, targetType, converterType);
         }
         else {
            body = getAdvice().handleEmptyBody(null, inputMessage, parameter, targetType, converterType);
         }
         break;
      }
   }
}

MappingJackson2HttpMessageConverter属于GenericHttpMessageConverter类型

 

spring反序列化参数

com.fasterxml.jackson.databind.deser.BeanDeserializer

/**
 * Main deserialization method for bean-based objects (POJOs).
 */
@Override
public Object deserialize(JsonParser p, DeserializationContext ctxt) throws IOException
{
    // common case first
    if (p.isExpectedStartObjectToken()) {
        if (_vanillaProcessing) {
            return vanillaDeserialize(p, ctxt, p.nextToken());
        }
        // 23-Sep-2015, tatu: This is wrong at some many levels, but for now... it is
        //    what it is, including "expected behavior".
        p.nextToken();
        if (_objectIdReader != null) {
            return deserializeWithObjectId(p, ctxt);
        }
        return deserializeFromObject(p, ctxt);
    }
    return _deserializeOther(p, ctxt, p.getCurrentToken());
}

/**
 * General version used when handling needs more advanced features.
 */
@Override
public Object deserializeFromObject(JsonParser p, DeserializationContext ctxt) throws IOException
{
    /* 09-Dec-2014, tatu: As per [#622], we need to allow Object Id references
     *   to come in as JSON Objects as well; but for now assume they will
     *   be simple, single-property references, which means that we can
     *   recognize them without having to buffer anything.
     *   Once again, if we must, we can do more complex handling with buffering,
     *   but let's only do that if and when that becomes necessary.
     */
    if (_objectIdReader != null && _objectIdReader.maySerializeAsObject()) {
        if (p.hasTokenId(JsonTokenId.ID_FIELD_NAME)
                && _objectIdReader.isValidReferencePropertyName(p.getCurrentName(), p)) {
            return deserializeFromObjectId(p, ctxt);
        }
    }
    if (_nonStandardCreation) {
        if (_unwrappedPropertyHandler != null) {
            return deserializeWithUnwrapped(p, ctxt);
        }
        if (_externalTypeIdHandler != null) {
            return deserializeWithExternalTypeId(p, ctxt);
        }
        Object bean = deserializeFromObjectUsingNonDefault(p, ctxt);
        if (_injectables != null) {
            injectValues(ctxt, bean);
        }
        /* 27-May-2014, tatu: I don't think view processing would work
         *   at this point, so commenting it out; but leaving in place
         *   just in case I forgot something fundamental...
         */
        /*
        if (_needViewProcesing) {
            Class<?> view = ctxt.getActiveView();
            if (view != null) {
                return deserializeWithView(p, ctxt, bean, view);
            }
        }
        */
        return bean;
    }
//先生成一个对象，值都为各个类型的默认值
    final Object bean = _valueInstantiator.createUsingDefault(ctxt);
    // [databind#631]: Assign current value, to be accessible by custom deserializers
    p.setCurrentValue(bean);
    if (p.canReadObjectId()) {
        Object id = p.getObjectId();
        if (id != null) {
            _handleTypedObjectId(p, ctxt, bean, id);
        }
    }
    if (_injectables != null) {
        injectValues(ctxt, bean);
    }
    if (_needViewProcesing) {
        Class<?> view = ctxt.getActiveView();
        if (view != null) {
            return deserializeWithView(p, ctxt, bean, view);
        }
    }
    if (p.hasTokenId(JsonTokenId.ID_FIELD_NAME)) {
        String propName = p.getCurrentName();
        do {
            p.nextToken();
            SettableBeanProperty prop = _beanProperties.find(propName);
            if (prop != null) { // normal case
                try {
                    prop.deserializeAndSet(p, ctxt, bean);
                } catch (Exception e) {
                    wrapAndThrow(e, bean, propName, ctxt);
                }
                continue;
            }
            handleUnknownVanilla(p, ctxt, bean, propName);
        } while ((propName = p.nextFieldName()) != null);
    }
    return bean;
}

com.fasterxml.jackson.databind.deser.impl.MethodProperty

@Override
public void deserializeAndSet(JsonParser p, DeserializationContext ctxt,
        Object instance) throws IOException
{
    Object value = deserialize(p, ctxt);
    try {
        _setter.invoke(instance, value);
    } catch (Exception e) {
        _throwAsIOE(p, e, value);
    }
}

StringDeserializer：对String类型的反序列化实现
所在包：com.fasterxml.jackson.databind.deser.std

 

@Override
public String deserialize(JsonParser p, DeserializationContext ctxt) throws IOException
{
    if (p.hasToken(JsonToken.VALUE_STRING)) {
        return p.getText();
    }
    JsonToken t = p.getCurrentToken();
    // [databind#381]
    if (t == JsonToken.START_ARRAY) {
        return _deserializeFromArray(p, ctxt);
    }
    // need to gracefully handle byte[] data, as base64
    if (t == JsonToken.VALUE_EMBEDDED_OBJECT) {
        Object ob = p.getEmbeddedObject();
        if (ob == null) {
            return null;
        }
        if (ob instanceof byte[]) {
            return ctxt.getBase64Variant().encode((byte[]) ob, false);
        }
        // otherwise, try conversion using toString()...
        return ob.toString();
    }
    // allow coercions for other scalar types
    String text = p.getValueAsString();
    if (text != null) {
        return text;
    }
    return (String) ctxt.handleUnexpectedToken(_valueClass, p);
}

 

BooleanDeserializer：对布尔类型的反序列化
所在包：com.fasterxml.jackson.databind.deser.std

@Override
public Boolean deserialize(JsonParser j, DeserializationContext ctxt) throws IOException
{
    return _parseBoolean(j, ctxt);
}

protected final Boolean _parseBoolean(JsonParser p, DeserializationContext ctxt)
    throws IOException
{
    JsonToken t = p.getCurrentToken();
    if (t == JsonToken.VALUE_TRUE) {
        return Boolean.TRUE;
    }
    if (t == JsonToken.VALUE_FALSE) {
        return Boolean.FALSE;
    }
    // should accept ints too, (0 == false, otherwise true)
    if (t == JsonToken.VALUE_NUMBER_INT) {
        return Boolean.valueOf(_parseBooleanFromInt(p, ctxt));
    }
    if (t == JsonToken.VALUE_NULL) {
        return (Boolean) getNullValue(ctxt);
    }
    // And finally, let's allow Strings to be converted too
    if (t == JsonToken.VALUE_STRING) {
        String text = p.getText().trim();
        // [databind#422]: Allow aliases
        if ("true".equals(text) || "True".equals(text)) {
            return Boolean.TRUE;
        }
        if ("false".equals(text) || "False".equals(text)) {
            return Boolean.FALSE;
        }
        if (text.length() == 0) {
            return (Boolean) getEmptyValue(ctxt);
        }
        if (_hasTextualNull(text)) {
            return (Boolean) getNullValue(ctxt);
        }
        return (Boolean) ctxt.handleWeirdStringValue(_valueClass, text,
                "only \"true\" or \"false\" recognized");
    }
    // [databind#381]
    if (t == JsonToken.START_ARRAY && ctxt.isEnabled(DeserializationFeature.UNWRAP_SINGLE_VALUE_ARRAYS)) {
        p.nextToken();
        final Boolean parsed = _parseBoolean(p, ctxt);
        t = p.nextToken();
        if (t != JsonToken.END_ARRAY) {
            handleMissingEndArrayForSingle(p, ctxt);
        }            
        return parsed;            
    }
    // Otherwise, no can do:
    return (Boolean) ctxt.handleUnexpectedToken(_valueClass, p);
}

protected boolean _parseBooleanFromInt(JsonParser p, DeserializationContext ctxt)
    throws IOException
{
    // 13-Oct-2016, tatu: As per [databind#1324], need to be careful wrt
    //    degenerate case of huge integers, legal in JSON.
    //  ... this is, on the other hand, probably wrong/sub-optimal for non-JSON
    //  input. For now, no rea

    // Anyway, note that since we know it's valid (JSON) integer, it can't have
    // extra whitespace to trim.
    //如果是在bool类型中传入数字，这个数字只要不是0都会解析会true
    return !"0".equals(p.getText());
}