How to use the Google Java client to load data into an existing BQ table?

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To use the Google Java client to load data into an existing BQ table, follow these steps:

1. Include the necessary libraries in your Java project by adding the following dependencies to your pom.xml file:

   <dependency>
       <groupId>com.google.cloud</groupId>
       <artifactId>google-cloud-bigquery</artifactId>
       <version>1.35.0</version>
   </dependency>
   <dependency>
       <groupId>com.google.api-client</groupId>
       <artifactId>google-api-client</artifactId>
       <version>1.32.1</version>
   </dependency>
   

2. Create a BigQuery instance using the BigQueryOptions class:

   BigQuery bigquery = BigQueryOptions.newBuilder()
       .setProjectId(projectId)
       .build().getService();
   

   Replace projectId with the ID of the project containing the BQ table you want to load data into.

3. Create a TableId instance for the table you want to load data into:

   TableId tableId = TableId.of(projectId, datasetId, tableId);
   

   Replace datasetId with the ID of the dataset containing the table, and tableId with the ID of the table.

4. Create a TableDataWriteChannel instance to write data to the table:

   TableDataWriteChannel writer = bigquery.writer().write(tableId);
   OutputStream stream = Channels.newOutputStream(writer);
   

5. Serialize your data and write it to the OutputStream:

   String data = "[{\"name\":\"John\", \"age\": 30}, {\"name\":\"Jane\", \"age\": 25}]";
   stream.write(data.getBytes());
   

   Replace data with the JSON representation of your data.

6. Close the channel to complete the upload:

   writer.close();
   

Your data should now be uploaded to the BQ table.