How to convert a complex JSON to CSV in Java

Question

I am having a complex.json file and I want it to convert into CSV file using Java Spring boot.

Below is my complex.json file:

{
  "requestId": "1P02XV425KCASEZGQLB8LPQMF4ZXCURRR01",
  "recyleBinRecords": [
    {
      "Record": {
        "ProductName": "Name1",
        "Id": "1P02XV425KCASEZGQLB8LPQMF4ZXCUBCTA01"
        "ProductArea": "Area1"
      },
      "dependecyMaterial": [
        {
          "Name": "D1",
          "id": "1P02XV425KCASEZGQLB8LPQMF4ZXCUBCTA01",
          "parentid": "1P02XV425KCASEZGQLB8LPQMF4ZXCUBCTA01",
          "value": "Value1"
        },
        {
          "Name": "d2",
          "id": "1P02XV425KCASEZGQLB8LPQMF4ZXCUBCTA01",
          "parentid": "1P02XV425KCASEZGQLB8LPQMF4ZXCUBCTA01",
          "value": "value2"
        }]},{
      "Record": {
        "ProductName": "Name2",
        "Id": "1P02XV425KCASEZGQLB8LPQMF4ZXCUBCTA01",
        "ProductArea": "Product2"
      },
      "dependecyMaterial": [
        {
          "Name": "D3",
          "id": "1P02XV425KCASEZGQLB8LPQMF4ZXCUBCTA01",
          "parentid": "P1",
          "value": "value1"
        },
        {
          "Name": "D4",
          "id": "1P02XV425KCASEZGQLB8LPQMF4ZXCUBCTA01",
          "parentid": "P2",
          "value": "value2"
        }
      ]
    }
  ]
}

Below is code I tried but it's giving no column exception.

JsonNode jsonTree = new ObjectMapper().readTree(new File("src/main/resources/complex.json"));
Builder csvSchemaBuilder = CsvSchema.builder();
JsonNode firstObject = jsonTree.elements().next();
firstObject.fieldNames().forEachRemaining(fieldName -> {csvSchemaBuilder.addColumn(fieldName);} );
CsvSchema csvSchema = csvSchemaBuilder.build().withHeader();

CsvMapper csvMapper = new CsvMapper();
csvMapper.writerFor(JsonNode.class)
  .with(csvSchema)
  .writeValue(new File("src/main/resources/orderLines.csv"), jsonTree);Copy

Need a solution to convert my JSON to CSV in java.

Could you provide more error details (stack trace)? Also, you need a comma (,) on the 7th line (after "Id": "1P02XV425KCASEZGQLB8LPQMF4ZXCUBCTA01"). — Albina
– Albina, Commented Dec 19, 2022 at 18:22

Vini · Accepted Answer · 2022-12-19 20:53:54Z

There are a couple of things that are causing this. Main reason for the exception you are getting is that your csv schema does not have columns to map. Run a debugger and see what the line JsonNode firstObject = jsonTree.elements().next(); returns and what fields are added to the schema when you run firstObject.fieldNames().forEachRemaining(fieldName -> {csvSchemaBuilder.addColumn(fieldName);} );

Having said that, the parsing may still not go through as CSV generator does not support nested Objects. There are several ways to handle this. You can write a custom method to handle the structure and spit out flattened data or use a library to handle the transformation. One way that I have done it in the past is by using the JOLT library (json to json transform) to pre-process the JSON and create an interim document and parsing it. See details in this answer - Return a JSON response as CSV file from spring-boot controller

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