Spring之DAO一

前面博客把bean、aop简单了解了一下，今天主要是了解Spring中DAO层，如果使用传统的JDBC时需要创建连接、打开、执行sql、关闭连接这一系列的步骤，Spring框架对JDBC进行了封装，我们只需使用封装好的JdbcTemplate执行sql语句。主要还是继承了Spring提供的JdbcDaoSupport。下面主要是用来演示怎么使用JdbcDaoSupport。

一、创建Model

这里创建一个User类，作为model。

package Cuiyw.Spring.Model;

public class User {
    private int userId;
    public int getUserId() {
        return userId;
    }
    public void setUserId(int userId) {
        this.userId = userId;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    private String name;
    
    
    private float money;
    public float getMoney() {
        return money;
    }
    public void setMoney(float money) {
        this.money = money;
    }

}
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二、创建DAO接口并实现接口

1.这里创建IUserDAO接口，声明了两个方法，一个是获取所有的User，一个是新增User。

package Cuiyw.Spring.IDao;

import java.util.*;

import Cuiyw.Spring.Model.User;

public interface IUserDAO {
    
    public List<User>QueryAllUser();
    
    public Boolean AddUser(String name,float money);
    
}
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2.这里实现接口IUserDAO,并且继承JdbcDaoSupport。在下面的代码中能找到getJdbcTemplate()，其实我们右键选择Open declaration 时可以定位到抽象类JdbcDaoSupport，JdbcDaoSupport里面有一个JdbcTemplate属性，而且还有get或set JDBC DataSource，然后选中JdbcTemplate，再Open declaration,发现JdbcTemplate的构造函数需要DataSource，JdbcDaoSupport提供JdbcTemplate对象，并维护着JdbcTemplate对象需要的DataSource。

package Cuiyw.Spring.Dao;

import java.util.*;

import org.springframework.jdbc.core.support.JdbcDaoSupport;

import Cuiyw.Spring.IDao.IUserDAO;
import Cuiyw.Spring.Model.User;


public class UserDAO extends JdbcDaoSupport implements IUserDAO {

    public List<User> QueryAllUser() {
        
        String sql="select id,name,money from tb_user";
        List<Map<String,Object>> list=getJdbcTemplate().queryForList(sql);
        List<User> userList=new ArrayList<User>();
        for(Map<String,Object> row:list)
        {
            User user=new User();
            user.setUserId((Integer)row.get("id"));
            user.setName((String)row.get("name"));
            user.setMoney((Float)row.get("money"));
            userList.add(user);
        }
        return userList;
        
    }

    public Boolean AddUser(String name,float money) {
        String sql="insert into tb_user (name,money) values (?,?)";
        int row=getJdbcTemplate().update(sql, new Object[]{name,money});
        if(row>0)
        {
            return true;
        }
        return false;
    }

}
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    public JdbcTemplate(DataSource dataSource) {
        setDataSource(dataSource);
        afterPropertiesSet();
    }
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3.上下文配置

上面DataSource从哪里来呢?就需要在上下文中配置。首先配置DataSource，然后由于UserDAO继承了抽象类JdbcDaoSupport，所以也需要设置属性dataSource

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:context="http://www.springframework.org/schema/context"
xmlns:mvc="http://www.springframework.org/schema/mvc"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:aop="http://www.springframework.org/schema/aop"
xsi:schemaLocation="
http://www.springframework.org/schema/beans
http://www.springframework.org/schema/beans/spring-beans.xsd
http://www.springframework.org/schema/context
http://www.springframework.org/schema/context/spring-context.xsd
http://www.springframework.org/schema/mvc
http://www.springframework.org/schema/mvc/spring-mvc.xsd
http://www.springframework.org/schema/aop
http://www.springframework.org/schema/aop/spring-aop.xsd
">
<bean id="dataSource" class="org.apache.commons.dbcp.BasicDataSource">
  <property name="driverClassName"> 
          <value>com.mysql.jdbc.Driver</value>
  </property>
  <property name="url">
          <value>jdbc:mysql://localhost:3306/spring</value>
  </property>
  <property name="username">
          <value>root</value>
  </property>
  <property name="password">
      <value>123456</value>
  </property> 
</bean> 
<bean id="userDao" class="Cuiyw.Spring.Dao.UserDAO" depends-on="dataSource">
    <property name="dataSource" ref="dataSource"></property>
</bean>
</beans>
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4.Mysql新增数据库和表

上面2中UserDAO执行了两个sql，涉及到表tb_user，字段id、name、money。在3上下文配置mysql时指定了数据库名spring。所以按照上面的创建。

5.实验

        ApplicationContext context=new ClassPathXmlApplicationContext(new String[]{"ApplicationContext.xml"});
        BeanFactory factory=context;
        IUserDAO userDao=(IUserDAO)factory.getBean("userDao");
        userDao.AddUser("cuiywA",888);
    
        userDao.AddUser("cuiywB",666);
        List<User> list=userDao.QueryAllUser(); 
        for(User u:list)
        {
            System.out.println("name:"+u.getName()+" money: "+u.getMoney());
        }
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6.错误

在实现上面的步骤时报了好几个错误，有因为我疏忽的，还有数据类型和数据库不一直的，最重要的两个我这里也记录了下来。

1.下面的错误是由于缺少commons-dbcp.jar、commons-pool.jar导致的

Cannot find class [org.apache.commons.dbcp.BasicDataSource] for bean with name 'dataSource' defined in class path resource [ApplicationContext.xml]; nested exception is java.lang.ClassNotFoundException: org.apache.commons.dbcp.BasicDataSource

2.还有就是我在UserDAO中继承了JdbcDaoSupport，但就是没自动提示要引入的包，这个第一次没经验，百度了才指定需要引入spring-jdbc.jar.

3.忘记引入mysql驱动

Failed to obtain JDBC Connection; nested exception is org.apache.commons.dbcp.SQLNestedException: Cannot load JDBC driver class 'com.mysql.jdbc.Driver'

上面的错误都是没有引入jar包，这里把pom.xml也放进来，留着以后好用。

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
  <modelVersion>4.0.0</modelVersion>

  <groupId>Cuiyw</groupId>
  <artifactId>SpringAop</artifactId>
  <version>0.0.1-SNAPSHOT</version>
  <packaging>jar</packaging>

  <name>SpringAop</name>
  <url>http://maven.apache.org</url>

  <properties>
    <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
      <spring.version>5.0.0.RELEASE</spring.version>
  </properties>

  <dependencies>
        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-core</artifactId>
            <version>${spring.version}</version>
        </dependency>
        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-context</artifactId>
            <version>${spring.version}</version>
        </dependency>
       
        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-jdbc</artifactId>
            <version>${spring.version}</version>
        </dependency>
        <dependency>
            <groupId>commons-dbcp</groupId>
            <artifactId>commons-dbcp</artifactId>
            <version>1.4</version>
        </dependency>
        <dependency>
            <groupId>commons-pool</groupId>
            <artifactId>commons-pool</artifactId>
            <version>1.6</version>
        </dependency>
        <!-- https://mvnrepository.com/artifact/mysql/mysql-connector-java -->
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>5.1.6</version>
        </dependency>
        
        <dependency>
          <groupId>junit</groupId>
          <artifactId>junit</artifactId>
          <version>3.8.1</version>
          <scope>test</scope>
        </dependency>
            <!-- https://mvnrepository.com/artifact/aspectj/aspectjweaver -->
        <dependency>
            <groupId>aspectj</groupId>
            <artifactId>aspectjweaver</artifactId>
            <version>1.5.4</version>
        </dependency>
            <!-- https://mvnrepository.com/artifact/aspectj/aspectjrt -->
        <dependency>
            <groupId>aspectj</groupId>
            <artifactId>aspectjrt</artifactId>
            <version>1.5.4</version>
        </dependency>
    
  </dependencies>
</project>
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原文地址：https://www.cnblogs.com/5ishare/p/8179110.html