Creating a table within a dataset in BigQuery programmatically

I haven't used the Java BigQuery library personally¹, but it looks like you should call BigQuery.create(TableInfo, TableOptions[]. That documentation has this example code - assuming you already have an instance of a BigQuery interface implementation of course:

String datasetName = "my_dataset_name";
String tableName = "my_table_name";
String fieldName = "string_field";
TableId tableId = TableId.of(datasetName, tableName);
// Table field definition
Field field = Field.of(fieldName, Field.Type.string());
// Table schema definition
Schema schema = Schema.of(field);
TableDefinition tableDefinition = StandardTableDefinition.of(schema);
TableInfo tableInfo = TableInfo.newBuilder(tableId, tableDefinition).build();
Table table = bigquery.create(tableInfo);

Obviously your schema construction is likely to be a bit more involved for a real table, but that should get you started. I can't see any way of loading a schema from a file, but if your schema file is machine-readable in a simple way (e.g. JSON) you could probably write your own parser fairly easily. (And contribute it to the project, should you wish...)

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¹ I'm the main author of the C# BigQuery library though, so I know what to look for.