I have a simple requirement where, if application encounters an exception,
my JAX-RS Rest endpoint should return a custom JSON response with 500 HTTP
header status.
Data needed to construct the response comes from an object with several
properties (see below). The problem is, I am only interested in one or two
values from each property (out of several dozens). And I cannot modify any
of these models/classes (some have a Jackson annotation for JSON
processing, e.g. null properties should be discarded during serialization).
public class MainObject {
private FirstProperty firstProperty;
private SecondProperty secondProperty;
private ThirdProperty thirdProperty;
// other codes
public String toString() {
ObjectMapper mapper = new ObjectMapper();
try { return mapper.writeValueAsString(this); }
catch (Exception e) { return null; }
}
}
public class FirstProperty {
private boolean bol = true;
private double dob = 5.0;
private List<String> subProperty;
// other properties
public String toString() {
ObjectMapper mapper = new ObjectMapper();
try { return mapper.writeValueAsString(this); }
catch (Exception e) { return null; }
}
}
@JsonSerialize(include=JsonSerialize.Inclusion.NON_NULL)
public class SecondProperty {
private String str;
private List<String> subProperty;
// other properties
public String toString() {
ObjectMapper mapper = new ObjectMapper();
try { return mapper.writeValueAsString(this); }
catch (Exception e) { return null; }
}
}
@JsonSerialize(include=JsonSerialize.Inclusion.NON_NULL)
public class ThirdProperty {
private int intProp = true;
private List<String> subProperty;
// other properties
public String toString() {
ObjectMapper mapper = new ObjectMapper();
try { return mapper.writeValueAsString(this); }
catch (Exception e) { return null; }
}
}
The expected JSON that I should be seeing coming back is on the client side
(say, a browser -- testing in Edge):
{
"firstProperty" : { "subProperty" : [ "val1" ] },
"secondProperty" : { "str" : "val2", "subproperty" : [ "val3", "val6"
] },
"thirdProperty" : { "subProperty" : [ "val4" ] }
}
Instead, all my field names and their values have their quotations escaped,
and extra double quotes around the entire value, e.g.:
{
"firstProperty" : "{ \"subProperty\" : [ \"val1\" ] }",
"secondProperty" : "{ \"str\" : \"val2\", \"subproperty\" : [
\"val3\", \"val6\" ] }",
"thirdProperty" : "{ \"subProperty\" : [ \"val4\" ] }"
}
Please note the extra `"` before and after the curly brackets. My
environment is:
Java 1.8.45
FasterXML Jackson 2.9.8
Spring Boot 2.0.1
RestEasy (JBoss) JAX-RS
JBoss 6.4
I eliminated the majority of "noise" in the code to see at what point this
happens. This is the controller:
@Path("/"
public class MainController {
@GET
@Produces(MediaType.APPLICATION_JSON)
@Path("/rest/path")
public MainObject getMainObject throws MyCustomException {
// A service call that throws MyCustomException
}
}
And JAX-RS `ExceptionMapper` where I send the response back:
@Provider
public class MyCustomExceptionMapper extends
ExceptionMapper<MyCustomException> {
@Override
public Response toResponse(MyCustomException ex) {
HashMap<String, Object> responseBody = new HashMap<>();
String strEx = ex.getStrEx(); // Comes from SecondProperty.str
stored in MyCustomException, not that it matters
// Instantiate an empty object that contains
MainObject obj = new MainObject();
obj.getFirstProperty().setSubProperty(ex.getStrs());
obj.getSecondProperty().setStr(strEx);
obj.getSecondProperty().setSubProperty(ex.getStrs());
obj.getThirdProperty().setSubProperty(ex.getStrs());
responseBody.put("firstProperty",
serializeFirstProperty(obj.getFirstProperty()));
responseBody.put("secondProperty",
serializeSecondProperty(obj.getSecondProperty()));
responseBody.put("thirdProperty",
serializeThirdProperty(obj.getThirdProperty()));
Response response = Response.status(/* 500 status
*/).entity(responseBody).build();
return response;
}
}
Since I only need to send back a very small subset of overall properties
from each of my types, I created a custom `StdSerializer` that would only
populate a needed property. For brevity, I only do
`serializeFirstProperty()` but they are all more or less identical:
public StdSerializer<FirstProperty> getFPSerializer(FirstProperty
firstProperty) {
return new StdSerializer<FirstProperty>(FirstProperty.class) {
@Override
public void serialize(FirstProperty value, JsonGenerator gen,
SerializerProvider provider) throws IOException {
gen.writeStartObject();
if (/* there are items in FirstProperty.subProperty */) {
gen.writeArrayFieldStart("subProperty");
for (String str : value.getSubProperty())
gen.writeString(str);
gen.writeEndArray();
}
gen.writeEndObject();
}
}
public <T> ObjectMapper getCustomOM(StdSerializer<?> serializer) {
ObjectMapper mapper = new ObjectMapper();
SimpleModule sm = new SimpleModule();
sm.addSerializer(serializer);
mapper.registerModule(module);
return mapper;
}
Then use these helper methods like:
public String serializeFirstProperty(FirstProperty firstProperty) {
ObjectMapper mapper = getCustomOM(getFPSerializer(firstProperty));
String ser = null;
try { ser = mapper.writeValueAsString(firstProperty); }
catch (JsonProcessingException e) { return null; }
return ser;
}
I have tried countless of configurations with `ObjectMapper`, e.g.
`disable(JsonParser.Feature.ALLOW_BACKLASH_ESCAPING_ANY_CHARACTER)`
(couldn't find any relevant flag for `JsonGenerator` which I really want to
disable in a similar fashion).
Or explicitly returning `Object` from `serializeFirstProperty()`.
Or set custom `StdSerializer`'s `JsonGenerator.setCharacterEscapes(new
CharacterEscapes() { //... }` or play around with JAX-RS `Response` at no
avail. I always seem to get a "string" value with quotations, e.g.:
"firstProperty" : "{ \"subProperty\" : [ \"val1\" ] }"
If I simply just do
responseBody.put("firstProperty",
mapper.writeValueAsString(obj.getFirstProperty()));
somehow this produces the right JSON output, however, it includes a lot of
unnecessary properties which I don't want in this exception handling case.
Funny thing is, when I peer into `response` (or `responseBody` map),
everything looks right (I don't see values having double quotations).
Please also note that not only I can't modify the models, but some of their
properties are instantiated during creation with default values, so
not-null inclusion doesn't work, and they will appear in the final JSON if
I don't use a custom serialization.
Does anyone know what's causing this escaped and extra quotations?
--
You received this message because you are subscribed to the Google Groups
"jackson-user" group.
To unsubscribe from this group and stop receiving emails from it, send an email
to [email protected].
To post to this group, send email to [email protected].
To view this discussion on the web visit
https://groups.google.com/d/msgid/jackson-user/ef031f10-e369-466d-9418-1ade1e37bf2f%40googlegroups.com.
For more options, visit https://groups.google.com/d/optout.
