The goal of this library is to support input data integrity when loading json data into Apache Spark. For this purpose the library:
- Reads in an existing json-schema file
- Parses the json-schema and builds a Spark DataFrame schema
The generated schema can be used when loading json data into Spark. This verifies that the input data conforms to the given schema and enables to filter out corrupt input data.
Include the library under the following coordinates:
libraryDependencies += "org.zalando" %% "spark-json-schema" % "0.6.1"
Parse a given json-schema file by providing the path to the input file. This file should be relative to the resources folder:
val schema = SchemaConverter.convert("schemaFile.json")
Alternatively you can use convertContent with the schema json content as a string. This means you can use any file loader to access your schema.json file and put the resulting string into this function. So this file may be stored anywhere:
val schema = SchemaConverter.convertContent(<schema json as string>)
Use the created schema when loading json-files into Spark:
val dataFrame = sqlContext.read.schema(schema).json(source)
Jsons that are not according to the schema have only
null in the dataFrame fields and can be filtered out:
val filteredData = dataFrame.rdd.filter( x => Range(0, x.length).contains(!x.isNullAt(_)))
After these steps you can be sure that all files that were loaded for further processing comply to your schema.
The root of the schema json is required to be type 'object' and to have a field 'properties' having the contents of the schema. Currently supported types are: "string", "number" (double), "float", "integer" (long), "boolean", "object" and "array"
The root level may have a field called 'definitions' having additional structures. These structures can be referenced in the schema. This might be useful, if you have certain objects that are used multiple times. In order to use such a reference in the schema the corresponding field name should be '$ref'. The value is the address in the definitions, i.e. the path following the first occurrence of 'definitions/' will be applied on the definitions field. So a reference will look like:
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