简单 jdbcTemplate.query() 应该是 return 一个列表，但不是

Question

我正在使用 spring 4.0（启动），代码如下：

        String sql = "SELECT emp_id,name,role FROM employees";
        List<Employee> employees = jdbcTemplate.query(sql,(rs, rowNum)-> 
        new Employee(rs.getInt("emp_id"), rs.getString("name"),
                rs.getString("role")));         
        employees.forEach(employee -> {log.info(employee.toString());
            log.info("part a");});

代码看起来简单明了，但问题是员工在日志中根本没有返回任何内容。这是否意味着 employees 中的所有内容都是空的？

记录器本身应该没有问题，因为这段代码之前的记录工作。

数据库输入正确。当我通过 mysql 客户端查询时，我可以在那里看到它们。

我犯了什么样的 Java 错误（如果是的话）？

编辑：这是我执行简单数据库查询的完整功能，上面的代码来自：

    @Override
    public void run(String... args) throws Exception {
        log.info("Creating tables");

        jdbcTemplate.execute("DROP TABLE IF EXISTS employee");
        jdbcTemplate.execute("CREATE TABLE employee (emp_id int, name varchar(100), role varchar(100))");

        log.info("Inserting Baggins Hopkins");
        int rowsAffected = jdbcTemplate.update("INSERT INTO EMPLOYEE(EMP_ID, NAME, ROLE)"
                + " VALUES(1,'Baggins Hopkins','thief')");
        log.info("rows affected: "+ Integer.toString(rowsAffected));
        int rowsAffected1 = jdbcTemplate.update("INSERT INTO EMPLOYEE(EMP_ID, NAME, ROLE)"
                + " VALUES(2,'Doolous Hopkins','robber')");
        log.info("rows affected: "+ Integer.toString(rowsAffected1));
        log.info("Querying for employee");
        String sql = "SELECT emp_id,name,role FROM employee";
        List<Employee> employees = jdbcTemplate.query(sql,(rs, rowNum)-> 
        new Employee(rs.getInt("emp_id"), rs.getString("name"),
                rs.getString("role")));
        log.info("Part A:");
        log.info(String.valueOf(employees.isEmpty()));
//      List<Employee> employees = new ArrayList<Employee>();
//      final List<Map<String, Object>> rows = jdbcTemplate.queryForList(sql);
//      for(final Map row : rows) {
//          Employee employee = new Employee();
//          employee.setId((int)row.get("emp_id"));
//          employee.setName((String)row.get("name"));
//          employee.setRole((String)row.get("role"));
//      };

        employees.forEach(employee -> {log.info(employee.toString());
            log.info("part a");});

    }

这是出错时的日志：

 :: Spring Boot ::        (v2.1.0.RELEASE)

2018-11-07 22:08:36.599  INFO 5476 --- [           main] c.j.jdbctest1.JdbcTest1Application       : Starting JdbcTest1Application on KitKat with PID 5476 (C:\Users\Nano\Downloads\jdbc-test1\jdbc-test1\target\classes started by Nano in C:\Users\Nano\Downloads\jdbc-test1\jdbc-test1)
2018-11-07 22:08:36.599  INFO 5476 --- [           main] c.j.jdbctest1.JdbcTest1Application       : No active profile set, falling back to default profiles: default
2018-11-07 22:08:37.458  INFO 5476 --- [           main] c.j.jdbctest1.JdbcTest1Application       : Started JdbcTest1Application in 1.156 seconds (JVM running for 2.08)
2018-11-07 22:08:37.474  INFO 5476 --- [           main] c.j.jdbctest1.JdbcTest1Application       : Creating tables
2018-11-07 22:08:37.474  INFO 5476 --- [           main] com.zaxxer.hikari.HikariDataSource       : HikariPool-1 - Starting...
2018-11-07 22:08:37.614  INFO 5476 --- [           main] com.zaxxer.hikari.HikariDataSource       : HikariPool-1 - Start completed.
2018-11-07 22:08:38.873  INFO 5476 --- [           main] c.j.jdbctest1.JdbcTest1Application       : Inserting Baggins Hopkins
2018-11-07 22:08:39.042  INFO 5476 --- [           main] c.j.jdbctest1.JdbcTest1Application       : rows affected: 1
2018-11-07 22:08:39.183  INFO 5476 --- [           main] c.j.jdbctest1.JdbcTest1Application       : rows affected: 1
2018-11-07 22:08:39.183  INFO 5476 --- [           main] c.j.jdbctest1.JdbcTest1Application       : Querying for employee
2018-11-07 22:08:39.214  INFO 5476 --- [           main] c.j.jdbctest1.JdbcTest1Application       : Part A:
2018-11-07 22:08:39.214  INFO 5476 --- [           main] c.j.jdbctest1.JdbcTest1Application       : true
2018-11-07 22:08:39.230  INFO 5476 --- [       Thread-1] com.zaxxer.hikari.HikariDataSource       : HikariPool-1 - Shutdown initiated...
2018-11-07 22:08:39.230  INFO 5476 --- [       Thread-1] com.zaxxer.hikari.HikariDataSource       : HikariPool-1 - Shutdown completed.

Answer 1

您可以使用其他方式获取员工列表：

private static final RowMapper<Employee> ROW_MAPPER = BeanPropertyRowMapper.newInstance(Employee.class);

String sql = "SELECT emp_id,name,role FROM employees";
List<Employee> employees = jdbcTemplate.query(sql, ROW_MAPPER);

或

List<Employee> employees = jdbcTemplate.queryForList(sql, Employee.class);

Answer 2

发帖人的回答：

这是一个简单的语法错误。正如评论员指出的那样，我一直在插入错误的 table... 我在 sql 查询中的语法错误。

之前，我插入 'employees,' 但我应该插入 'employee.'

queryForList() returns 一个包含 Map 的 List，但是，仍然 returns null。我在上面的 post 中评论了这一点。我不知道那有什么问题（我之前没有尝试过使用 List> ）。不过问题已经解决了。

简单 jdbcTemplate.query() 应该是 return 一个列表，但不是

Simple jdbcTemplate.query() is supposed to return a list, but isn't

java

mysql

arrays

jdbctemplate

spring-boot