• 它是如何运作的
• 相关文件
  • 分页运行器.java
  • 架构.sql
  • 数据.sql
• 示例输出

// package and import lines removed for brevity 
@Component
public class PaginationRunner implements ApplicationRunner {Logger logger = LoggerFactory.getLogger(PaginationRunner.class);/**  * The pageSize is configurable. We default it to 5 here.  * You can override it in the src/main/resources/application.properties file by setting pagination_runner.page_size.  * Or, via env var by setting PAGINATION_RUNNER_PAGE_SIZE.  */@Value("${pagination_runner.page_size:5}")private int pageSize;/**  * The jdbcTemplate uses the default data source. Which, in this demo, is the in-memory H2 database.  */@Autowiredprivate JdbcTemplate jdbcTemplate;/**  * This class implements ApplicationRunner.  * So, this component will run after the Spring Application Context is initialized.  */@Overridepublic void run(ApplicationArguments args) throws Exception {logger.info("Starting PaginationRunner");loopThroughThePages();logger.info("Finished PaginationRunner");}/**  * Loop through the pages until you encounter an empty page.  */private void loopThroughThePages() {Pageable pageable = PageRequest.of(0, pageSize);Page<Map<String, Object>> page = findAll(pageable);while (!page.isEmpty()) {logProgress(pageable, page);page.stream().forEach(this::handleRow);pageable = pageable.next();page = findAll(pageable);}}/**  * Find all the rows.  * You _could_ create the query using LIMIT and OFFSET...  * But, I went with a plain WHERE clause that selects a range of IDs because it's faster.  */private Page<Map<String, Object>> findAll(Pageable pageable) {long startId = pageable.getOffset();long endId = startId + pageable.getPageSize();String sql = String.format("SELECT * FROM word WHERE id > %s AND id <= %s",startId,endId);logger.info("findAll sql: {}", sql);List<Map<String, Object>> rows = jdbcTemplate.queryForList(sql);long total = countAll();return new PageImpl<>(rows, pageable, total);}/**  * Count all the rows.  */private long countAll() {String sql = "SELECT COUNT(*) FROM word";logger.info("countAll sql: {}", sql);return jdbcTemplate.queryForObject(sql, Long.class);}/**  * Log the progress.  * You'll thank yourself for this, especially if the "job" is long-running.  */private void logProgress(Pageable pageable, Page<Map<String, Object>> page) {int currentPage = pageable.getPageNumber() + 1;int totalPages = page.getTotalPages();int currentRowCount = page.getNumberOfElements();long totalRowCount = page.getTotalElements();logger.info("On page {} of {}. Rows in page: {}. Total rows: {}",currentPage, totalPages, currentRowCount, totalRowCount);}/**  * Actually do something with each row.  * In this demo, I'm just logging the row.  * In a real scenario, maybe you're building up a bulk request to send somewhere else, etc.  */private void handleRow(Map<String, Object> row) {logger.info(row.toString());}}

-- When using the in-memory H2 database, this is how the schema is defined. 
CREATE TABLE word (id INT AUTO_INCREMENT PRIMARY KEY,word CHARACTER VARYING
);

-- When using the in-memory H2 database, this is how the data is seeded. -- I got this data by grepping for words starting with "b" in the built-in Mac dictionary at /usr/share/dict/words. 
INSERT INTO word (word) VALUES ('babblesome');
INSERT INTO word (word) VALUES ('babbling');
INSERT INTO word (word) VALUES ('babblingly');
INSERT INTO word (word) VALUES ('babblish');
INSERT INTO word (word) VALUES ('babblishly');
INSERT INTO word (word) VALUES ('babbly');
INSERT INTO word (word) VALUES ('babby');
INSERT INTO word (word) VALUES ('babe');
INSERT INTO word (word) VALUES ('babehood');
INSERT INTO word (word) VALUES ('babelet');
INSERT INTO word (word) VALUES ('babelike');