Problem4J Jackson

In order to serialize or deserialize Problem objects into JSON (or XML) using Jackson (aka ObjectMapper), you need to register appropriate module or MixIn-annotation.

Because Jackson v3 has been released with different Maven groupId, it's technically possible to include both Jackson v2 and v3 within a single project, as two separate dependencies. Therefore, there are two modules for integrating Problem4J with Jackson - problem4j-jackson2 and problem4j-jackson3.

Integration with Jackson v2

There are in fact three ways, ObjectMapper can find out how to serialize and deserialize Problem objects.

1. Registering ProblemModule in ObjectMapper manually.

   import com.fasterxml.jackson.databind.ObjectMapper;
   import io.github.problem4j.jackson2.ProblemModule;
   
   ObjectMapper mapper = new ObjectMapper().registerModule(new ProblemModule());

2. Registering ProblemModule in ObjectMapper automatically with findAndRegisterModules method.

   import com.fasterxml.jackson.databind.ObjectMapper;
   
   ObjectMapper mapper = new ObjectMapper().findAndRegisterModules();

3. Registering ProblemMixIn in ObjectMapper.

   import com.fasterxml.jackson.databind.ObjectMapper;
   import io.github.problem4j.core.Problem;
   import io.github.problem4j.jackson2.ProblemMixIn;
   
   ObjectMapper mapper = new ObjectMapper().addMixIn(Problem.class, ProblemMixIn.class);

With proper setup of ObjectMapper, following code will handle Problem objects properly.

import io.github.problem4j.core.Problem;

// ...

Problem problem = 
    Problem.builder()
        .title("Bad Request")
        .status(400)
        .detail("not a valid json")
        .build();

String json = mapper.writeValueAsString(problem);
Problem parsed = mapper.readValue(json, Problem.class);

Dependencies for Jackson v2 integration

Add library as dependency to Maven or Gradle. See the actual versions on Maven Central. Java 8 or higher is required to use problem4j-jackson2 library. Note that problem4j-jackson2 module does not declare jackson-databind as a transitive dependency.

1. Maven:

   <dependencies>
       <dependency>
           <groupId>com.fasterxml.jackson.core</groupId>
           <artifactId>jackson-databind</artifactId>
           <version>2.20.1</version>
       </dependency>
       <dependency>
           <groupId>io.github.problem4j</groupId>
           <artifactId>problem4j-core</artifactId>
           <version>1.3.0</version>
       </dependency>
       <dependency>
           <groupId>io.github.problem4j</groupId>
           <artifactId>problem4j-jackson2</artifactId>
           <version>1.3.0</version>
       </dependency>
   </dependencies>

2. Gradle (Kotlin DSL):

   dependencies {
       implementation("com.fasterxml.jackson.core:jackson-databind:2.20.0")
       implementation("io.github.problem4j:problem4j-core:1.3.0")
       implementation("io.github.problem4j:problem4j-jackson2:1.3.0")
   }

Integration with Jackson v3

There are in fact three ways, JsonMapper can find out how to serialize and deserialize Problem objects.

1. Registering ProblemJacksonModule in JsonMapper manually.

   import io.github.problem4j.jackson3.ProblemJacksonModule;
   import tools.jackson.databind.JsonMapper;
   
   JsonMapper mapper = JsonMapper.builder().addModule(new ProblemJacksonModule()).build();

2. Registering ProblemJacksonModule in JsonMapper automatically with findAndAddModules method.

   import tools.jackson.databind.JsonMapper;
   
   JsonMapper mapper = JsonMapper.builder().findAndAddModules().build();

3. Registering ProblemJacksonMixIn in JsonMapper.

   import io.github.problem4j.core.Problem;
   import io.github.problem4j.jackson3.ProblemJacksonMixIn;
   import tools.jackson.databind.JsonMapper;
   
   JsonMapper mapper = JsonMapper.builder().addMixIn(Problem.class, ProblemJacksonMixIn.class).build();

With proper setup of JsonMapper, following code will handle Problem objects properly.

import io.github.problem4j.core.Problem;

// ...

Problem problem = 
    Problem.builder()
        .title("Bad Request")
        .status(400)
        .detail("not a valid json")
        .build();

String json = mapper.writeValueAsString(problem);
Problem parsed = mapper.readValue(json, Problem.class);

Note that for integration with Jackson v3, both module and MixIn-annotation include *Jackson* phrase in their names. This was done to match naming style with Jackson itself as Jackson v3 had renamed Module base class to JacksonModule.

Dependencies for Jackson v3 integration

Add library as dependency to Maven or Gradle. See the actual versions on Maven Central. Java 17 or higher is required to use problem4j-jackson3 library. Note that problem4j-jackson3 module does not declare jackson-databind as a transitive dependency.

1. Maven:

   <dependencies>
       <dependency>
           <groupId>tools.jackson.core</groupId>
           <artifactId>jackson-databind</artifactId>
           <version>3.0.3</version>
       </dependency>
       <dependency>
           <groupId>io.github.problem4j</groupId>
           <artifactId>problem4j-core</artifactId>
           <version>1.3.0</version>
       </dependency>
       <dependency>
           <groupId>io.github.problem4j</groupId>
           <artifactId>problem4j-jackson3</artifactId>
           <version>1.3.0</version>
       </dependency>
   </dependencies>

2. Gradle (Kotlin DSL):

   dependencies {
       implementation("tools.jackson.core:jackson-databind:3.0.3")
       implementation("io.github.problem4j:problem4j-core:1.3.0")
       implementation("io.github.problem4j:problem4j-jackson3:1.3.0")
   }