Various Drupal 8 Body Migration Techniques Ways

migrate-way-1.php

use Drupal\migrate\Plugin\MigrationInterface;
use Drupal\migrate\Plugin\MigrateSourceInterface;
use Drupal\migrate\Row;

/**
 * Implements hook_migrate_prepare_row().
 */
function YOUR_MODULE_migrate_prepare_row(Row $row, MigrateSourceInterface $source, MigrationInterface $migration) {
  switch ($migration->id()) {
    case 'config_name':
      $body = $row->getSourceProperty('body');
      $row->setSourceProperty('body_value', $body[0]['value']);
      $row->setSourceProperty('body_summary', $body[0]['summary']);
      $row->setSourceProperty('body_format', $body[0]['format']);
      break;
  }
}

migrate-way-1.yml

process:
  'body/value': body_value
  'body/summary': body_summary
  'body/format':
    plugin: static_map
    source: body_format
    map:
      full_html: full_html
      filtered_html: basic_html
      pure_html: full_html
      plain_text: plain_text
      php_code: full_html

migrate-way-2.yml

process:
  body:
    plugin: sub_process
    source: body
    process:
      value: value
      summary: summary
      format:
        plugin: static_map
        source: format
        map:
          full_html: full_html
          filtered_html: basic_html
          pure_html: full_html
          plain_text: plain_text
          php_code: full_html

migrate-way-3.yml

source:
  constants:
    format: basic_html
process:
  body/value:
    plugin: extract
    source: body
    index:
      - 0
      - value
  body/format: constants/format