关于SpringBoot集成JDBCTemplate的RowMapper

　　　　　　JdbcTemplate 是Spring提供的一套JDBC模板框架，利用AOP 技术来解决直接使用JDBC时大量重复代码的问题。JdbcTemplate虽然没有MyBatis 那么灵活，但是直接使用JDBC要方便很多。Spring Boot中对Jdbc Template的使用提供了自动化配置类JdbcTemplateAutoConfiguration，部分源码如下：

package org.springframework.boot.autoconfigure.jdbc;

// 省略 import 行

@Configuration
// 仅在类 DataSource,JdbcTemplate 存在于 classpath 时生效,
// 这两个类属于 spring-jdbc
@ConditionalOnClass({ DataSource.class, JdbcTemplate.class })
// 仅在单数据源bean存在时才生效
@ConditionalOnSingleCandidate(DataSource.class)
// 在数据源自动配置应用之后应用
@AutoConfigureAfter(DataSourceAutoConfiguration.class)
// 确保前缀为 spring.jdbc 的配置参数被加载到 bean JdbcProperties
@EnableConfigurationProperties(JdbcProperties.class)
public class JdbcTemplateAutoConfiguration {

    // 内嵌配置类
    @Configuration
    static class JdbcTemplateConfiguration {

        private final DataSource dataSource;

        private final JdbcProperties properties;

        JdbcTemplateConfiguration(DataSource dataSource, JdbcProperties properties) {
            this.dataSource = dataSource;
            this.properties = properties;
        }

       // 定义 bean  JdbcTemplate jdbcTemplate       
        @Bean
        @Primary
        // 仅在此bean没有被定义时才定义
        @ConditionalOnMissingBean(JdbcOperations.class)
        public JdbcTemplate jdbcTemplate() {
            JdbcTemplate jdbcTemplate = new JdbcTemplate(this.dataSource);
            JdbcProperties.Template template = this.properties.getTemplate();
            jdbcTemplate.setFetchSize(template.getFetchSize());
            jdbcTemplate.setMaxRows(template.getMaxRows());
            if (template.getQueryTimeout() != null) {
                jdbcTemplate
                        .setQueryTimeout((int) template.getQueryTimeout().getSeconds());
            }
            return jdbcTemplate;
        }

    }

    // 内嵌配置类
    @Configuration
    // 导入 JdbcTemplateConfiguration 配置类
    @Import(JdbcTemplateConfiguration.class)
    static class NamedParameterJdbcTemplateConfiguration {

        // 定义 bean NamedParameterJdbcTemplate namedParameterJdbcTemplate
        @Bean
        @Primary
        @ConditionalOnSingleCandidate(JdbcTemplate.class)
        @ConditionalOnMissingBean(NamedParameterJdbcOperations.class)
        public NamedParameterJdbcTemplate namedParameterJdbcTemplate(
                JdbcTemplate jdbcTemplate) {
            return new NamedParameterJdbcTemplate(jdbcTemplate);
        }

    }
      ......  
}    

　　从上面这段源码中可以看出，当classpath下存在DataSource和JdbcTemplate 并且DataSource只有一个实例时，自动配置才会生效，若开发者没有提供JdbcOperations，则Spring Boot会自动向容器中注入一个JdbcTemplate（Jdbc Template是JdbcOperations的子类）。由此可以看到，开发者想要使用Jdbc Template，只需要提供JdbcTemplate的依赖和DataSource依赖即可。具体操作步骤

 

1，创建数据库表并插入数据　　

CREATE DATABASE 'chapter05'DEFAULT CHARACTER SET utf8;
USE‘chapter05;
CREATE TABLE book(
id int(11)NOT NULL AUTO INCREMENT,
name varchar(128)DEFAULT NULL,
author varchar(64)DEFAULT NULL,
PRIMARY KEY('id')
ENGINE=InnoDB DEFAULT CHARSET=utf8;
insert into book'(id,name,author)values(1,'三国演义，罗贯中'），（2，'水浒传'，'施耐庵'）；

 

2，添加依赖

<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-jdbc</artifactId>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-web</artifactId>
</dependency>
<dependency>
<groupId>mysql</groupId>
<artifactId>mysql-connector-java</artifactId>
<scope>runtime</scope>
</dependency>
<dependency>
<groupId>com.alibaba</groupId>
<artifactId>druid</artifactId>
<version>1.1.9</version>
</dependency>

 

3.数据库配置（注意数据库的配置）
在application.properties中配置数据库基本连接信息：

spring.datasource.type=com.alibaba.druid.pool.DruidDataSource
spring.datasource.url=jdbc:mysql:///chapter05
spring.datasource.username=root（你自己的）
spring.datasource.password=123（你自己的密码，没有不用填）

 

4.创建实体类,

创建Book实体类，代码如下：

public class Book{
private Integer id;
private String name;
private String author;
//省略 getter/setter

}

 

 

5.创建数据库访问层

@Repository
public class BookDao {
    @Autowired
    JdbcTemplate jdbcTemplate;
    public int addBook(Book book) {
        return jdbcTemplate.update("INSERT INTO book(name,author) VALUES (?,?)",
                book.getName(), book.getAuthor());
    }
    public int updateBook(Book book) {
        return jdbcTemplate.update("UPDATE book SET name=?,author=? WHERE id=?",
                book.getName(), book.getAuthor(), book.getId());
    }
    public int deleteBookById(Integer id) {
        return jdbcTemplate.update("DELETE FROM book WHERE id=?", id);
    }
    public Book getBookById(Integer id) {
        return jdbcTemplate.queryForObject("select * from book where id=?",
                new BeanPropertyRowMapper<>(Book.class), id);
    }
    public List<Book> getAllBooks() {
        return jdbcTemplate.query("select * from book",
                new BeanPropertyRowMapper<>(Book.class));
    }
}

代码解释：

创建BookDao，注入Jdbc Template。由于已经添加了spring-jdbc相关的依赖，JdbcTemplate会被自动注册到Spring容器中，因此这里可以直接注入Jdbc Template使用。在JdbcTemplate中，增删改三种类型的操作主要使用update和batchUpdate方法来完成。query和queryForObject方法主要用来完成查询功能。另外，还有execute方法可以用来执行任意的SQL、cal方法用来调用存储过程等。·在执行查询操作时，需要有一个/RowMapper f查询出来的列和实体类中的属性一一对应起）来。如果列名和属性名都是相同的，那么可以直接使用BeanPropertyRowMapper；如果列名和属性名不同就需要开发者自己实见RowMapper 接口，将列和实体类属性一一对应起来。

6.创建Service和Controller
创建BookService和BookController，代码如下：

BookService

@Service
public class BookService {
    @Autowired
    BookDao bookDao;
    public int addBook(Book book) {
        return bookDao.addBook(book);
    }
    public int updateBook(Book book) {
        return bookDao.updateBook(book);
    }
    public int deleteBookById(Integer id) {
        return bookDao.deleteBookById(id);
    }
    public Book getBookById(Integer id) {
        return bookDao.getBookById(id);
    }
    public List<Book> getAllBooks() {
        return bookDao.getAllBooks();
    }
}

BookController

package org.sang;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;

import java.util.List;

/**
 * Created by 半仙
 */
@RestController
public class BookController {
    @Autowired
    BookService bookService;
    @GetMapping("/bookOps")
    public void bookOps() {
        Book b1 = new Book();
        b1.setId(99);
        b1.setName("西厢记");
        b1.setAuthor("王实甫");
        int i = bookService.addBook(b1);
        System.out.println("addBook>>>" + i);
        Book b2 = new Book();
        b2.setId(1);
        b2.setName("朝花夕拾");
        b2.setAuthor("鲁迅");
        int updateBook = bookService.updateBook(b2);
        System.out.println("updateBook>>>"+updateBook);
        Book b3 = bookService.getBookById(1);
        System.out.println("getBookById>>>"+b3);
        int delete = bookService.deleteBookById(2);
        System.out.println("deleteBookById>>>"+delete);
        List<Book> allBooks = bookService.getAllBooks();
        System.out.println("getAllBooks>>>"+allBooks);
    }
}

最后，在浏览器中访问http://localhost：8080/bookOps地址，控制台打印日志如图5-1所示
addBook>〉>1
updateBoolk>〉>1
getBookById>>>Book{id=1,name='朝花夕拾’，author='鲁迅’}
deleteBoolkById>>>1
getA11Books>>>[Book{id=1,name='朝花夕拾’，author='鲁迅’}，Book{id=4，name='西厢记’，author='王实甫’}]

 

　　这里只是介绍SpringBoot集成JDBCTemplate的Demo，重点在于上面说的这句话“·在执行查询操作时，需要有一个/RowMapper f查询出来的列和实体类中的属性一一对应起）来。如果列名和属性名都是相同的，那么可以直接使用BeanPropertyRowMapper；如果列名和属性名不同就需要开发者自己实见RowMapper 接口，将列和实体类属性一一对应起来。”

　　那么在上面我们看到，JdbcTemplate已经封装了对应增删改的方法，我们只需直接调用即可，关键在于query查询时候RowMapper的这点上，正如上面所说，如果列名和属性名都是相同的，我们可以直接使用BeanPropertyRowMapper，如果列名和属性名不同就需要开发者自己实见RowMapper 接口，将列和实体类属性一一对应起来。”

　　那么到底这个RowMapper是什么 ，官方的源码如下

package org.springframework.jdbc.core;

import java.sql.ResultSet;
import java.sql.SQLException;
import org.springframework.lang.Nullable;

@FunctionalInterface
public interface RowMapper<T> {
    @Nullable
    T mapRow(ResultSet var1, int var2) throws SQLException;
}

　　不难看出这是一个方法接口 ，里面的抽象法中的ResultSet又是什么呢 ，表示数据库结果集的数据表，通常由执行查询数据库的语句生成，这里我只贴出官方的版本，想看的直接点击ctrl+鼠标左键点进去看，我用的是IDEA

**
 * A table of data representing a database result set, which
 * is usually generated by executing a statement that queries the database.
 *
 * <P>A <code>ResultSet</code> object  maintains a cursor pointing
 * to its current row of data.  Initially the cursor is positioned
 * before the first row. The <code>next</code> method moves the
 * cursor to the next row, and because it returns <code>false</code>
 * when there are no more rows in the <code>ResultSet</code> object,
 * it can be used in a <code>while</code> loop to iterate through
 * the result set.
 * <P>
 * A default <code>ResultSet</code> object is not updatable and
 * has a cursor that moves forward only.  Thus, you can
 * iterate through it only once and only from the first row to the
 * last row. It is possible to
 * produce <code>ResultSet</code> objects that are scrollable and/or
 * updatable.  The following code fragment, in which <code>con</code>
 * is a valid <code>Connection</code> object, illustrates how to make
 * a result set that is scrollable and insensitive to updates by others, and
 * that is updatable. See <code>ResultSet</code> fields for other
 * options.
 * <PRE>
 *
 *       Statement stmt = con.createStatement(
 *                                      ResultSet.TYPE_SCROLL_INSENSITIVE,
 *                                      ResultSet.CONCUR_UPDATABLE);
 *       ResultSet rs = stmt.executeQuery("SELECT a, b FROM TABLE2");
 *       // rs will be scrollable, will not show changes made by others,
 *       // and will be updatable
 *
 * </PRE>
 * The <code>ResultSet</code> interface provides
 * <i>getter</i> methods (<code>getBoolean</code>, <code>getLong</code>, and so on)
 * for retrieving column values from the current row.
 * Values can be retrieved using either the index number of the
 * column or the name of the column.  In general, using the
 * column index will be more efficient.  Columns are numbered from 1.
 * For maximum portability, result set columns within each row should be
 * read in left-to-right order, and each column should be read only once.
 *
 * <P>For the getter methods, a JDBC driver attempts
 * to convert the underlying data to the Java type specified in the
 * getter method and returns a suitable Java value.  The JDBC specification
 * has a table showing the allowable mappings from SQL types to Java types
 * that can be used by the <code>ResultSet</code> getter methods.
 *
 * <P>Column names used as input to getter methods are case
 * insensitive.  When a getter method is called  with
 * a column name and several columns have the same name,
 * the value of the first matching column will be returned.
 * The column name option is
 * designed to be used when column names are used in the SQL
 * query that generated the result set.
 * For columns that are NOT explicitly named in the query, it
 * is best to use column numbers. If column names are used, the
 * programmer should take care to guarantee that they uniquely refer to
 * the intended columns, which can be assured with the SQL <i>AS</i> clause.
 * <P>
 * A set of updater methods were added to this interface
 * in the JDBC 2.0 API (Java&trade; 2 SDK,
 * Standard Edition, version 1.2). The comments regarding parameters
 * to the getter methods also apply to parameters to the
 * updater methods.
 *<P>
 * The updater methods may be used in two ways:
 * <ol>
 * <LI>to update a column value in the current row.  In a scrollable
 *     <code>ResultSet</code> object, the cursor can be moved backwards
 *     and forwards, to an absolute position, or to a position
 *     relative to the current row.
 *     The following code fragment updates the <code>NAME</code> column
 *     in the fifth row of the <code>ResultSet</code> object
 *     <code>rs</code> and then uses the method <code>updateRow</code>
 *     to update the data source table from which <code>rs</code> was derived.
 * <PRE>
 *
 *       rs.absolute(5); // moves the cursor to the fifth row of rs
 *       rs.updateString("NAME", "AINSWORTH"); // updates the
 *          // <code>NAME</code> column of row 5 to be <code>AINSWORTH</code>
 *       rs.updateRow(); // updates the row in the data source
 *
 * </PRE>
 * <LI>to insert column values into the insert row.  An updatable
 *     <code>ResultSet</code> object has a special row associated with
 *     it that serves as a staging area for building a row to be inserted.
 *     The following code fragment moves the cursor to the insert row, builds
 *     a three-column row, and inserts it into <code>rs</code> and into
 *     the data source table using the method <code>insertRow</code>.
 * <PRE>
 *
 *       rs.moveToInsertRow(); // moves cursor to the insert row
 *       rs.updateString(1, "AINSWORTH"); // updates the
 *          // first column of the insert row to be <code>AINSWORTH</code>
 *       rs.updateInt(2,35); // updates the second column to be <code>35</code>
 *       rs.updateBoolean(3, true); // updates the third column to <code>true</code>
 *       rs.insertRow();
 *       rs.moveToCurrentRow();
 *
 * </PRE>
 * </ol>
 * <P>A <code>ResultSet</code> object is automatically closed when the
 * <code>Statement</code> object that
 * generated it is closed, re-executed, or used
 * to retrieve the next result from a sequence of multiple results.
 *
 * <P>The number, types and properties of a <code>ResultSet</code>
 * object's columns are provided by the <code>ResultSetMetaData</code>
 * object returned by the <code>ResultSet.getMetaData</code> method.
 *
 * @see Statement#executeQuery
 * @see Statement#getResultSet
 * @see ResultSetMetaData
 */

 

　　如何实现自己的RowMapper？参照如下代码

public class BeanRowMapper implements RowMapper<Article> {
　　//这里的类名只是为了掩饰   根据自己的情况修改
    @Override
    public Article mapRow(ResultSet resultSet, int i) throws SQLException {
        Bean bean= new Bean();
　　　　　　//设置不一致的列名与实体字段对应
        bean.setId(resultSet.getInt("id"));
        bean.setTitle(resultSet.getString("title"));
        bean.setDescription(resultSet.getString("description"));
        return Bean;
    }

}

　　然后修改对应的Dao代码

/**
 * 查询所有数据
 */
public List<Bean> findAll() {
    String sql = "SELECT id, title, description FROM Bean";
    return jdbcTemplate.query(sql, new BeanRowMapper());
}

/**
 * 查询单条数据
 */
public BeanfindById(Integer id) {
    String sql = "SELECT id, title, description FROM BeanWHERE id = ?";
    return jdbcTemplate.queryForObject(sql, new BeanRowMapper());
}

　　然后在测试对应的接口

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