我的问题相当简单：我有一个如下的简单类：
public class Foo {
private int id = -1;
public void setId(int _id){ this.id = _id; }
public int getId(){ return this.id; }
}
我正在尝试处理以下JSON：
{
"id": "blah"
}
很明显，这里存在问题（"blah" 无法解析为 int）
以前，Jackson会抛出类似于 org.codehaus.jackson.map.JsonMappingException：无法从字符串值“blah”构建 java.lang.Integer 实例：不是一个有效的整数值
我同意这一点，但我想在某个地方注册一些内容，允许忽略这种类型的映射错误。我尝试了注册 DeserializationProblemHandler（参见此处），但它似乎只适用于未知属性，而不是反序列化问题。
你对这个问题有什么线索吗？
public class JacksonNonBlockingObjectMapperFactory {
/**
* Deserializer that won't block if value parsing doesn't match with target type
* @param <T> Handled type
*/
private static class NonBlockingDeserializer<T> extends JsonDeserializer<T> {
private StdDeserializer<T> delegate;
public NonBlockingDeserializer(StdDeserializer<T> _delegate){
this.delegate = _delegate;
}
@Override
public T deserialize(JsonParser jp, DeserializationContext ctxt) throws IOException, JsonProcessingException {
try {
return delegate.deserialize(jp, ctxt);
}catch (JsonMappingException e){
// If a JSON Mapping occurs, simply returning null instead of blocking things
return null;
}
}
}
private List<StdDeserializer> jsonDeserializers = new ArrayList<StdDeserializer>();
public ObjectMapper createObjectMapper(){
ObjectMapper objectMapper = new ObjectMapper();
SimpleModule customJacksonModule = new SimpleModule("customJacksonModule", new Version(1, 0, 0, null));
for(StdDeserializer jsonDeserializer : jsonDeserializers){
// Wrapping given deserializers with NonBlockingDeserializer
customJacksonModule.addDeserializer(jsonDeserializer.getValueClass(), new NonBlockingDeserializer(jsonDeserializer));
}
objectMapper.registerModule(customJacksonModule);
return objectMapper;
}
public JacksonNonBlockingObjectMapperFactory setJsonDeserializers(List<StdDeserializer> _jsonDeserializers){
this.jsonDeserializers = _jsonDeserializers;
return this;
}
}
然后以这种方式进行调用（只传递那些你想要非阻塞的反序列化器）：
JacksonNonBlockingObjectMapperFactory factory = new JacksonNonBlockingObjectMapperFactory();
factory.setJsonDeserializers(Arrays.asList(new StdDeserializer[]{
// StdDeserializer, here, comes from Jackson (org.codehaus.jackson.map.deser.StdDeserializer)
new StdDeserializer.ShortDeserializer(Short.class, null),
new StdDeserializer.IntegerDeserializer(Integer.class, null),
new StdDeserializer.CharacterDeserializer(Character.class, null),
new StdDeserializer.LongDeserializer(Long.class, null),
new StdDeserializer.FloatDeserializer(Float.class, null),
new StdDeserializer.DoubleDeserializer(Double.class, null),
new StdDeserializer.NumberDeserializer(),
new StdDeserializer.BigDecimalDeserializer(),
new StdDeserializer.BigIntegerDeserializer(),
new StdDeserializer.CalendarDeserializer()
}));
ObjectMapper om = factory.createObjectMapper();
@ExceptionHandler(HttpMessageNotReadableException.class)
@ResponseBody
public String handleHttpMessageNotReadableException(HttpMessageNotReadableException ex)
{
JsonMappingException jme = (JsonMappingException) ex.getCause();
return jme.getPath().get(0).getFieldName() + " invalid";
}
当然，这句话
JsonMappingException jme = (JsonMappingException) ex.getCause();
有些情况下可能会抛出类转换异常，但我还没有遇到过。
if(ex.getCause() instanceof JsonMappingException)（如果不是，则适当的逻辑来重新抛出或委托处理其他异常类型）可以消除任何可能出现 ClassCastException 的情况。否则，答案很有用。 - StormeHawkepublic class JacksonExceptionHandler {
public String getErrorMessage(HttpMessageNotReadableException e) {
String message = null;
boolean handled = false;
Throwable cause = e.getRootCause();
if (cause instanceof UnrecognizedPropertyException) {
UnrecognizedPropertyException exception = (UnrecognizedPropertyException) cause;
message = handleUnrecognizedPropertyException(exception);
handled = true;
}
if (cause instanceof InvalidFormatException) {
InvalidFormatException exception = (InvalidFormatException) cause;
message = handleInvalidFormatException(exception);
handled = true;
}
if (cause instanceof MismatchedInputException) {
if (!handled) {
MismatchedInputException exception = (MismatchedInputException) cause;
message = handleMisMatchInputException(exception);
}
}
if (cause instanceof JsonParseException) {
message = "Malformed json";
}
return message;
}
private String handleInvalidFormatException(InvalidFormatException exception) {
String reference = null;
if (!exception.getPath().isEmpty()) {
String path = extractPropertyReference(exception.getPath());
reference = removeLastCharacter(path);
}
Object value = exception.getValue();
return "Invalid value '" + value + "' for property : " + reference;
}
private String handleUnrecognizedPropertyException(UnrecognizedPropertyException exception) {
String reference = null;
if (!exception.getPath().isEmpty()) {
String path = extractPropertyReference(exception.getPath());
reference = removeLastCharacter(path);
}
return "Unknown property : '" + reference + "'";
}
private String handleMisMatchInputException(MismatchedInputException exception) {
String reference = null;
if (!exception.getPath().isEmpty()) {
reference = extractPropertyReference(exception.getPath());
}
String property = StringUtils.substringBetween(exception.getLocalizedMessage(), "'", "'");
// if property missing inside nested object
if (reference != null && property!=null) {
return "Missing property : '" + reference + property + "'";
}
// if invalid value given to array
if(property==null){
return "Invalid values at : '"+ reference +"'";
}
// if property missing at root level
else return "Missing property : '" + property + "'";
}
// extract nested object name for which property is missing
private String extractPropertyReference(List<JsonMappingException.Reference> path) {
StringBuilder stringBuilder = new StringBuilder();
path.forEach(reference -> {
if(reference.getFieldName() != null) {
stringBuilder.append(reference.getFieldName()).append(".");
// if field is null means it is array
} else stringBuilder.append("[].");
}
);
return stringBuilder.toString();
}
// remove '.' at the end of property path reference
private String removeLastCharacter(String string) {
return string.substring(0, string.length() - 1);
}
}
可以在全局通知中调用此类对象，如下所示
@Override
protected ResponseEntity<Object> handleHttpMessageNotReadable(HttpMessageNotReadableException ex, HttpHeaders headers, HttpStatus status, WebRequest request) {
String message = new JacksonExceptionHandler().generator.getErrorMessage(ex);
if(message == null){
return ResponseEntity.badRequest().body("Malformed json");
}
return ResponseEntity.badRequest().body(message);
}
@Provider
@Produces(MediaType.APPLICATION_JSON)
public class JSONProcessingErroMapper implements ExceptionMapper<InvalidFormatException> {
@Override
public Response toResponse(InvalidFormatException ex) {
return Response.status(400)
.entity(new ClientError("[User friendly message]"))
.type(MediaType.APPLICATION_JSON)
.build();
}
}
DeserializationProblemHandler 现在有更多的方法，例如 handleUnexpectedToken 和 handleWeird*Value。它应该能够处理任何需要的内容。
继承它，覆盖你需要的方法，然后使用 addHandler(DeserializationProblemHandler h) 将其添加到你的 ObjectMapper 中。