Spring JdbcTemplate中關於RowMapper的使用實例

在spring boot 集成使用jdbctemplate，首先在pom文件中引入相應的依賴

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-jdbc</artifactId>
        </dependency>
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>5.1.34</version>
            <scope>runtime</scope>
        </dependency>

<!--整合druid數據源-->
<dependency>
 <groupId>com.alibaba</groupId>
 <artifactId>druid-spring-boot-starter</artifactId>
 <version>1.1.9</version>
</dependency>

yml中配置數據源：

#druid數據源
    druid:
      username: root
      password: 12345
      driver-class-name: com.mysql.jdbc.Driver
      url: jdbc:mysql://localhost:3306/corporationmanagement?useUnicode=true&characterEncoding=utf8
      initialSize: 1
      minIdle: 1
      maxActive: 5
      maxWait: 60000
      timeBetweenEvictionRunsMillis: 60000
      minEvictableIdleTimeMillis: 300000
      validationQuery: SELECT 1 FROM DUAL
      testWhileIdle: true
      testOnBorrow: false
      testOnReturn: false
      poolPreparedStatements: true
      maxPoolPreparedStatementPerConnectionSize: 20
      connectionProperties: druid.stat.mergeSql=true;druid.stat.slowSqlMillis=5000

 

本文就來先解釋下什么是Row Mapper，我們該如何正確地使用。

    @Override
    public Student getStudentByName(String name) {
        String sql = "select name, gender from test_student where name = ?";
        Student student = this.jdbcTemplate.queryForObject(sql, new Object[]{name}, new RowMapper<Student>() {
            @Override
            public Student mapRow(ResultSet rs, int i) throws SQLException {
                Student s = new Student();
                s.setName(rs.getString("name"));
                s.setGender(rs.getString("gender"));
                return s;
            }
        });
        return student;
    }

    @Override
    public List<Student> getStudentsByName(String name) {
        String sql = "select name, gender from test_student where name = ?";
        List<Student> students = this.jdbcTemplate.query(sql, new Object[]{name}, new RowMapper<Student>() {
            @Override
            public Student mapRow(ResultSet rs, int i) throws SQLException {
                Student s = new Student();
                s.setName(rs.getString("name"));
                s.setGender(rs.getString("gender"));
                return s;
            }
        });
        return students;
    }

 

一、RowMapper的基本使用

使用過原生JDBC的朋友應該知道，從數據庫查詢出來的記錄全都被保存在ResultSet結果集中，我們需要將結果集中的數據一條條地獲取並設置到具體的實體類上，如此，該實體類才能在接下來的程序中使用。然而問題是，每次都要這么操作實在是太麻煩了，Spring就不應該提供什么功能來替我們做這些事情嗎？答案當然是有的，那就是本文的主角——RowMapper。

Spring JDBC中目前有兩個主要的RowMapper實現，使用它們應該能解決大部分的場景了。

1.1 SingleColumnRowMapper

通過名字我們就能大概了解，在查詢返回單列數據的時候，就該使用這個RowMapper，下面我們來看看具體的代碼：

    @Override
    public String getStudentNameById(String id) {
        String sql = "select name from test_student where id = ?";
        return this.jdbcTemplate.queryForObject(sql, new Object[]{id},
                new SingleColumnRowMapper<>(String.class));
    }

    @Override
    public List<String> getStudentNamesByGrade(Integer grade) {
        String sql = "select name from test_student where grade = ?";
        return this.jdbcTemplate.query(sql, new Object[]{grade},
                new SingleColumnRowMapper<>(String.class));
    }

    @Test
    public void getStudentNameById(){
        String name = studentService.getStudentNameById("3");
        assertEquals("李清照", name);
    }

    @Test
    public void getStudentNamesByGrade(){
        List<String> names = studentService.getStudentNamesByGrade(1);
        assertTrue(2 == names.size());
    }

 

1.2 BeanPropertyRowMapper

當查詢數據庫返回的是多列數據，且你需要將這些多列數據映射到某個具體的實體類上，那么就該使用這個Row Mapper，下面是具體的使用代碼：

    @Override
    public Student getStudentByName2(String name) {
        String sql = "select name, gender from test_student where name = ?";
        return this.jdbcTemplate.queryForObject(sql, new Object[]{name},
                new BeanPropertyRowMapper<>(Student.class));
    }

    @Override
    public List<Student> getStudentsByName2(String name) {
        String sql = "select name, gender from test_student where name = ?";
        return this.jdbcTemplate.query(sql, new Object[]{name},
                new BeanPropertyRowMapper<>(Student.class));
    }

    @Test
    public void getStudentByName2(){
        Student student = studentService.getStudentByName2("杜甫");
        assertEquals("杜甫",student.getName());
        assertEquals("男",student.getGender());
    }

    @Test
    public void getStudentsByName2(){
        List<Student> studentList = studentService.getStudentsByName("Jack");
        assertTrue(2 == studentList.size());
    }

 

這種使用方式有一個前提，那就是數據庫SQL查出來的數據其列名與實體類中的屬性名是一致的，當然個數和順序可以不一致。比如數據庫SQL查出來的姓名列叫name，那么對應的實體類中的姓名也必須叫name，而不能叫studentName或者其它。

二、定義自己的RowMapper

當然，如果你SQL查詢出來的數據列名就是和實體類的屬性名不一樣，或者想按照自己的規則來裝配實體類，那么就可以定義並使用自己的Row Mapper。

public class StudentRowMapper implements RowMapper<Student> {

    @Override
    public Student mapRow(ResultSet rs, int i) throws SQLException {
        Student student = new Student();
        student.setName(rs.getString("name"));
        student.setGender(rs.getString("gender"));
        student.setEmail(rs.getString("email"));
        return student;
    }
}

    @Override
    public Student getStudentByName3(String name) {
        String sql = "select name, gender, email from test_student where name = ?";
        return this.jdbcTemplate.queryForObject(sql, new Object[]{name}, new StudentRowMapper());
    }

    @Override
    public List<Student> getStudentsByName3(String name) {
        String sql = "select name, gender, email from test_student where name = ?";
        return this.jdbcTemplate.query(sql, new Object[]{name}, new StudentRowMapper());
    }

    @Test
    public void getStudentByName3(){
        Student student = studentService.getStudentByName3("杜甫");
        assertEquals("杜甫",student.getName());
        assertEquals("男",student.getGender());
        assertEquals("dufu@tang", student.getEmail());
    }

    @Test
    public void getStudentsByName3(){
        List<Student> studentList = studentService.getStudentsByName3("李白");
        assertTrue(2 == studentList.size());
    }

 

作者：力羊
鏈接：https://www.jianshu.com/p/be60a81e2fe7
來源：簡書
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