{"id":123951,"date":"2024-06-20T17:38:00","date_gmt":"2024-06-20T14:38:00","guid":{"rendered":"https:\/\/www.javacodegeeks.com\/?p=123951"},"modified":"2024-06-20T12:27:44","modified_gmt":"2024-06-20T09:27:44","slug":"mapping-enums-and-strings-with-mapstruct","status":"publish","type":"post","link":"https:\/\/www.javacodegeeks.com\/mapping-enums-and-strings-with-mapstruct.html","title":{"rendered":"Mapping Enums and Strings with MapStruct"},"content":{"rendered":"

MapStruct<\/a> is a Java annotation processor that streamlines the implementation of mappings between Java beans, including complex scenarios such as converting Enums to Strings and vice versa. This article explores various enum to string mapping techniques using MapStruct<\/a>. <\/p>\n

1. Mapping an Enum to a String<\/h2>\n

Let’s say we have an Enum and want to map it to a String representation for various purposes like JSON serialization.<\/p>\n

1.1 Example<\/h3>\n

Define an Enum:<\/p>\n

Status.java<\/em><\/span><\/p>\n

\npublic enum Status {\n    ACTIVE, INACTIVE, PENDING\n}\n<\/pre>\n
1.2 MapStruct Mapper<\/h3>\n
We want to map the above enum to a string. Let’s define the Mapper interface:<\/p>\n
StatusMapper.java<\/em><\/span><\/p>\n
\n@Mapper\npublic interface StatusMapper {\n    \n    StatusMapper INSTANCE = Mappers.getMapper(StatusMapper.class);\n\n    String toString(Status status);\n}\n<\/pre>\n
Usage:<\/strong><\/p>\n
EnumToString.java<\/em><\/span><\/p>\n
\npublic class EnumToString {\n\n    public static void main(String[] args) {\n\n        Status status = Status.ACTIVE;\n        \/\/ Singleton instance\n        StatusMapper mapper = StatusMapper.INSTANCE;\n\n        \/\/ Handle a valid enum value\n        String statusString = mapper.toString(status);\n        System.out.println(statusString);\n    }\n}\n<\/pre>\n
Here, mapper.toString(Status status)<\/code> will return the string representation of the status<\/code> enum value.<\/p>\n
Output:<\/strong><\/p>\n
\nACTIVE\n<\/pre>\n
2. Mapping a String to an Enum<\/h2>\n
MapStruct can also convert strings back to enums. It attempts to match the string value with the corresponding enum constant name (case-sensitive). In this example, we convert a String to its corresponding Enum value, often required for deserializing JSON or handling user inputs.
 
<\/div> <\/div><\/p>\n
2.1 MapStruct Mapper<\/h3>\n
StatusMapper.java<\/em><\/span><\/p>\n
\n@Mapper\npublic interface StatusMapper {\n    StatusMapper INSTANCE = Mappers.getMapper(StatusMapper.class);\n\n    Status toEnum(String status);\n}\n\n<\/pre>\n
Usage:<\/strong><\/p>\n
\npublic class StringToEnum {\n\n    public static void main(String[] args) {\n\n        String statusString = \"INACTIVE\";\n        Status status = StatusMapper.INSTANCE.toEnum(statusString);\n        System.out.println(status); \n    }\n}\n\n<\/pre>\n
In this example, StatusMapper.toEnum(\"INACTIVE\")<\/code> will return the Status.INACTIVE<\/code> enum value.<\/p>\n
Note:<\/strong> If the string doesn’t match an existing enum constant, MapStruct throws an exception.<\/p>\n
3. Mapping an Enum to a Custom String<\/h2>\n
Sometimes, we might want to map an enum to a custom string representation that differs from the toString()<\/code> method. MapStruct’s @ValueMapping<\/code> annotation allows for such customization.<\/p>\n
3.1 MapStruct Mapper<\/h3>\n
StatusMapper.java<\/em><\/span><\/p>\n
\n@Mapper\npublic interface StatusMapper {\n\n    StatusMapper INSTANCE = Mappers.getMapper(StatusMapper.class);\n\n    @ValueMapping(source = \"PENDING\", target = \"Pending Approval\")\n    @ValueMapping(source = \"ACTIVE\", target = \"Active Status\")\n    @ValueMapping(source = \"INACTIVE\", target = \"Inactive Status\")\n    String toString(Status status);\n}\n<\/pre>\n
Here, StatusMapper.toString(Status status)<\/code> will map each enum value to a custom string representation defined in the @ValueMapping<\/code> annotations.<\/p>\n
Usage:<\/strong><\/p>\n
EnumToCustomString.java<\/em><\/span><\/p>\n
\npublic class EnumToCustomString {\n\n    public static void main(String[] args) {\n        \n        Status status = Status.ACTIVE;\n        \/\/ Singleton instance\n        StatusMapper mapper = StatusMapper.INSTANCE;\n        \n        String statusString = mapper.toString(status);\n        \/\/String statusString = StatusMapper.INSTANCE.toString(status);\n        System.out.println(statusString); \n    }\n}\n\n<\/pre>\n
Output:<\/strong><\/p>\n
\nActive Status\n<\/pre>\n
4. Mapping a Custom String to an Enum<\/h2>\n
Similar to mapping Enum to a custom String, we can convert from a custom String back to Enum.<\/p>\n
4.1 MapStruct Mapper with Reverse Mapping<\/h3>\n
MapStruct can leverage @InheritInverseConfiguration<\/code> to define reverse mappings, ensuring that the mapping from custom strings to Enums is the inverse of the mapping from Enums to custom strings.<\/p>\n
StatusMapper.java<\/em><\/span><\/p>\n
\n@Mapper\npublic interface StatusMapper {\n\n    StatusMapper INSTANCE = Mappers.getMapper(StatusMapper.class);\n    \n    @InheritInverseConfiguration(name = \"toString\")\n    Status toStatus(String statusString);\n}\n<\/pre>\n
Usage:<\/strong><\/p>\n
\npublic class EnumToCustomString {\n\n    public static void main(String[] args) {\n        \n        String customString = \"Pending Approval\";\n        Status status = StatusMapper.INSTANCE.toStatus(customString);\n        System.out.println(status); \/\/ Output: PENDING\n\n    }\n}\n<\/pre>\n
In this example, the toStatus(customString)<\/code> method uses @InheritInverseConfiguration<\/code> to reverse the logic defined in toString(status)<\/code>.<\/p>\n
5. Conclusion<\/h2>\n
In this article, we demonstrated how to map an enum to a string using MapStruct, covering various scenarios:<\/p>\n