Try.withCatch

[jainh]

When i want to try like as follows Try.witchCatch(()->a()).onFail().map(()->b()).. where b() throws an exception as well, it says b with unhandled exception, who do deal in such situation? we can not call from map or flatmap function that throws an exception?

[johnmcclean]

Hey @jainh, this is the expected behaviour by default, although Try can be configured to catch subsequent exceptions in map / flatMap.

You can use Try.of(value,Exceptions..) to configure Try such that it will capture any Exceptions thrown in subsequent methods.

The reason we don't do this be default is because it may hide errors in code and we felt it important that engineers make a conscious / deliberate decision to use it.

Your example

 Try.witchCatch(()->a())
     .onFail(...)
     .map(v->b(v));

Could become

   Try.of(null, Throwable.class)
       .map(__>a())
       .onFail(...)
       .map(v->b(v));

We see Try primarily as a data type that represents either an error or a successful value, rather than being primarily a trapper of exceptions (although it can be used for that purpose). An alternative to turning on full exception catching, is to use flatMap with a nested Try.withCatch

  Try.witchCatch(()->a())
     .onFail(...)
     .flatMap(v->Try.withCatch(()->b(v)));

[jainh]

@johnmcclean-aol I think i tried the last option , i just did now again, here is the snippet

 Try.withCatch(() -> decodeBase64(token))
                .onFail(e -> LOG.error("error in decoding base64 token string:{}",e))
                .flatMap(v -> Try.withCatch(()-> (JSONObject)new JSONParser().parse(v)))

But (JSONObject)new JSONParser().parse(v) inside flatmap show red swiggle line with unhandeled parse exception.

[johnmcclean]

Hmmm.. That seems strange. Try.withCatch takes a CheckedSupplier so it should compile. What version are you using?

This compiles for me (tested against cyclops-react 2.0.0-MI4)

public int throwsEx() throws Exception{
    return 0;
}
@Test
public void testExcept(){
    assertThat(Try.withCatch(()-> throwsEx())
            .map(i->i+" woo!")
            .onFail(System.out::println)
            .flatMap(e->Try.withCatch(()-> throwsEx()))
            .orElse(1),is(0));


}

If you are using cyclops-react (rather than cyclops-try) you could also use ExceptionSoftener.softenSupplier to soften the ParseException (but you shouldn't have too).

[jainh]

<dependency>
			<groupId>com.aol.cyclops</groupId>
			<artifactId>cyclops-try</artifactId>
			<version>7.2.3</version>
		</dependency>

I think this could IDE intellij i am using but let me run it then i will update you.

[jainh]

@johnmcclean-aol do you how to apply parallel operation on result return after successful flatmap operation and then collect them ?

[johnmcclean]

Please do. I think that version should compile also (as it is also using CheckedSupplier to handle Checked Exceptions e.g. https://github.com/aol/cyclops/blob/v7.2.0/cyclops-try/src/main/java/com/aol/cyclops/trycatch/Try.java#L224)

[johnmcclean]

@jainh Do you want to process a the result in parallel in some way? i.e. is it a Collection that you would convert to a Stream and execute in parallel? I can show an example of that below

 Try.withCatch(() -> decodeBase64(token))
            .onFail(e -> LOG.error("error in decoding base64 token string:{}",e))
            .flatMap(v -> Try.withCatch(()-> (JSONObject)new JSONParser().parse(v)))
            .map(this::processInParallel); //I think it's better to define a method for this


public List<Type> processInParallel(List<JSONType> data){
     return data.stream()
                .parallel()
                .map(this::process)
                .collect(Collectors.toList());

}

[jainh]

  Try<Map<String, String>, Throwable> jsonString = Try.withCatch(() -> decodeBase64(token))
                .onFail(e -> LOG.error("error in decoding base64 token string:{}",e))
                .flatMap(v -> Try.withCatch(()-> (JSONObject)(new JSONParser()).parse(v)))
                .onFail(e -> LOG.error("error in parsing token string:{}",e))
                .map(v -> convertToMap(new ObjectMapper().readValue(v, HashMap.class)));

but value in map v is expected to be JSONObject but it shows R. what i am trying to do : parse string to JSONObject convert it to Map and then to JWT map then to JWTClaimSet.

[jainh]

@johnmcclean-aol

  public JwtUserDto parseToken(String token) throws JwtTokenMalformedException {
        JwtUserDto u = null;
        Gson gson = new Gson();

       Map<String, Try<JWTClaimsSet, ParseException>> claimsSets = Try.withCatch(() -> decodeBase64(token))
                .onFail(e -> LOG.error("error in decoding base64 token string:{}",e))
                .flatMap(jsonString -> gson.fromJson(jsonString, new TypeToken<Map<String, Object>>(){}.getType()))
                .onFail(e -> LOG.error("error in parsing token string:{}",e))
                .map(jsonMap -> convertToMap((Map<String, Object>)jsonMap))
                .onFail(e -> LOG.error("error failed to convert to map of string -> string : {}",e))
                .map(tokenMap -> tokenMap.entrySet().stream()
                        .collect(Collectors.toMap(Map.Entry :: getKey, p -> convertToClaimsSet(p.getValue()))))
               .get();


       if(claimsSets != null && !claimsSets.isEmpty()) {
           Date today = new Date();
           u = new JwtUserDto();
           if(claimsSets.get("ACCESS_TOKEN").get().getExpirationTime().before(today)){
               throw new JwtTokenMalformedException("Token is expired ");
           }
           JWTClaimsSet idToken = claimsSets.get("ID_TOKEN").get();
           u.setId((String)idToken.getClaims().get("user_id"));
           u.setUsername(idToken.getSubject());
       }
        return u;
    }

    private Map<String, String> convertToMap(Map<String,Object> data){
        return data.entrySet()
                   .stream()
                   .filter(v -> Arrays.asList("ID_TOKEN","ACCESS_TOKEN").contains(v.getKey()))
                   .collect(Collectors.toMap(Map.Entry::getKey, p -> (String)p.getValue()));
    }

    private Try<JWTClaimsSet, ParseException> convertToClaimsSet(String jwtToken){
        Try<JWTClaimsSet, ParseException> claimsSets = Try.withCatch(() -> JWTParser.parse(jwtToken))
            .onFail(e -> LOG.error("failed to parser jwt token because of the following reason:{}", e))
            .flatMap(v -> Try.withCatch( () -> v.getJWTClaimsSet()))
            .onFail(e -> LOG.error("failed to parser jwt token because of the following reason:{}", e));
        return claimsSets;
    }

Does that look ok to you? just sanity check