Convert Java pojo to json String

Question

I have the following java class

public  class TabularDescriptor extends ReportDescriptor {

    private String generatorClass;
    private String targetClass;
    private String name;
    private String sublabel;
    private String reportName;
    private List<MappingMetadata> mappings = null;
    private List<TabularColumnGroup> columnGroups = null;
    private List<TabularStates> states = null;
:
:
     and its getters and settere

I have entity classes for each of those List like MappingMetadata,TabularColumnGroup,TabularStates. I want to get a json data for this pojo classes. What can I do for it.

And what is the use of

    public JSONObject toJSON() {
        JSONObject ret = new JSONObject();
        ret.put("generatorClass", this.generatorClass);
        ret.put("targetClass", this.targetClass);
        ret.put("name", this.name);
        :
        :
        return ret;
    }

And is there anyway I can display my json content on browser if yes how can I? Thanks.

Answer 1

I would recommend you to add Jackson to your project, it's rather easy to use.

<dependency>
    <groupId>com.fasterxml.jackson.core</groupId>
    <artifactId>jackson-databind</artifactId>
    <version>2.9.8</version>
</dependency>

And in Java Code can be used as so:

ObjectMapper objectMapper = new ObjectMapper();
String json = objectMapper.writeValueAsString(tabularDescriptor);
TabularDescriptor newTabularDescriptor = objectMapper.readValue(json, TabularDescriptor.class);

Answer 2

There are 2 libraries that deal with JSON serialization/deserialization using Java:

1. Jackson

   Another library for a Java serialization/deserialization(docs). A default choice for the JSON interaction within Java for the majority of developers. Comes completely embedded with all dependencies in spring-boot-starter-web and spring-boot-starter-webflux, dependency starters of Spring Boot - popular Java IOC/DI framework.

   Dependencies _{(databind is the main dependency, for annotations and additional features you will need more Jackson dependencies)}:

   Maven:

   <dependency>
       <groupId>com.fasterxml.jackson.core</groupId>
       <artifactId>jackson-databind</artifactId>
       <version>${jackson.version}</version>   
   </dependency>
   

   Gradle:

   dependencies {
      implementation "com.fasterxml.jackson.core:jackson-databind:${yourVersion}"
   }
   

   Serialization Snippet:

   TabularDescriptor tabularDescriptor = new TabularDescriptor();
   ObjectMapper mapper = new ObjectMapper();
   String json = mapper.writeValueAsString(tabularDescriptor);
   

2. Gson

   Google's library for a Java serialization/deserialization(docs).
   

   Dependencies:

   Gradle:

   dependencies { 
       implementation "com.google.code.gson:gson:${yourVersion}"
   }
   

   Maven:

   <dependency>
       <groupId>com.google.code.gson</groupId>
       <artifactId>gson</artifactId>
       <version>${gson.version}</version>
   </dependency>
   

   Serialization Snippet:

   TabularDescriptor tabularDescriptor = new TabularDescriptor();
   Gson gson = new Gson();
   String json = gson.toJson(obj);
   

Details worth noting: you have to have all getters/setters public for both complete serialization and complete deserialization of an object(in its simplest form). An empty constructor is a must in any case.

Reference information:

1. JSON in Java by Baeldung
2. Jackson vs Gson by Baeldung