原生servlet——如何连接数据库-白红宇

原生servlet——如何连接数据库

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发布时间：2019-03-12

本文共 5502 字，大约阅读时间需要 18 分钟。

项目结构与数据库配置

在开发一个基于 JDBC 的数据访问层时，确保项目结构清晰和数据库配置正确是实现CRUD操作的关键。

一、项目结构

按照功能模块划分包，确保类似下面结构：

com├── dao│   ├── impl│   │   ├── BaseDao.java│   │   └── StudentDao.java│   └── model│       ├── entity│       │   └── Student.java│       └── domain│           └── StudentDomain.java

二、数据库配置

确保 jdbc.properties 中有正确的数据库配置：

username=rootpassword=1234url=jdbc:mysql://localhost:3306/peixun?characterEncoding=UTF-8driverClassName=com.mysql.jdbc.Driver

三、通用数据访问接口

实现通用数据访问接口尽量减少代码重复：

package com.dao;public interface BaseDao
   
     {    
     T selectForOne(Class, String, Object... args);     List selectForMore(Class, String, Object... args); int update(String, Object... args);}

项目实现步骤

一、创建项目框架

建立位置结构：

mkdir -p src/main/java/com/dao/implmkdir -p src/main/java/com/model/entity

二、配置数据库

编写 jdbc.properties：

username=rootpassword=1234url=jdbc:mysql://localhost:3306/peixundriverClassName=com.mysql.jdbc.Driver

编写 JdbcUtils 工具类：

package com.utils;import com.mysql.jdbc.Driver;import org.apache.commons.dbutils.QueryRunner;import org.apache.commons.dbutils.handlers.BeanHandler;import org.apache.commons.dbutils.handlers.BeanListHandler;import org.springframework.jdbc.datasource.DriverManagerDataSource;import java.sql.DriverManager;import java.sql.SQLException;public class JdbcUtils {    private static ThreadLocal
    
      dataSource = new ThreadLocal<>();    static {        try {            ClassLoader classLoader = JdbcUtils.class.getClassLoader();            InputStream is = classLoader.getResourceAsStream("jdbc.properties");            Properties props = new Properties();            props.load(is);            dataSource.set((DriverManagerDataSource) DriverManager.createDataSource(props));        } catch (Exception e) {            e.printStackTrace();        }    }    public static Connection getConnection() {        try {            return dataSource.get().getConnection();        } catch (SQLException e) {            throw new RuntimeException("获取数据库连接失败", e);        }    }    public static void closeConnection(Connection connection) {        try {            if (connection != null) {                connection.close();            }        } catch (SQLException e) {            e.printStackTrace();        }    }}

三、实现通用 `BaseDao` 类

package com.dao.impl;import com.dao.BaseDao;import com.model.entity.Student;import org.apache.commons.dbutils.QueryRunner;import org.apache.commons.dbutils.handlers.BeanHandler;import org.apache.commons.dbutils.handlers.BeanListHandler;import com.utils.JdbcUtils;import java.util.List;import java.sql.Connection;import java.sql.SQLException;public class BaseDao
    
      implements BaseDao
     
       {    private QueryRunner queryRunner = new QueryRunner();    public T selectForOne(Class
      
        type, String sql, Object... args) {        Connection connection = JdbcUtils.getConnection();        try {            return getBean(type, sql, args);        } catch (SQLException e) {            throw new RuntimeException("获取单条数据失败", e);        } finally {            JdbcUtils.closeConnection(connection);        }    }    public List
       
         selectForMore(Class
        
          type, String sql, Object... args) {        Connection connection = JdbcUtils.getConnection();        try {            return listBeans(type, sql, args);        } catch (SQLException e) {            throw new RuntimeException("获取多个数据失败", e);        } finally {            JdbcUtils.closeConnection(connection);        }    }    private T getBean(Class
         
           type, String sql, Object... args) { try { return queryRunner.query(JdbcUtils.getConnection(), sql, new BeanHandler
          
           (type), args); } catch (SQLException e) { throw new RuntimeException("获取对象失败", e); } } private List
           
             listBeans(Class
            
              type, String sql, Object... args) { try { return queryRunner.query(JdbcUtils.getConnection(), sql, new BeanListHandler
             
              (type), args); } catch (SQLException e) { throw new RuntimeException("获取列表失败", e); } } public int update(String sql, Object... args) { Connection connection = JdbcUtils.getConnection(); try { return queryRunner.update(connection, sql, args); } catch (SQLException e) { throw new RuntimeException("执行更新操作失败", e); } finally { JdbcUtils.closeConnection(connection); } return -1; }}

四、在 `StudentDao` 中继承 `BaseDao`

package com.dao;public interface StudentDao extends BaseDao
    
      {}

五、实现 `StudentDao`

package com.dao.impl;import com.dao.StudentDao;import com.model.entity.Student;import com.utils.JdbcUtils;public class StudentDao implements StudentDao {}

测试验证

创建测试类：

package com;import com.dao.impl.BaseDao;import com.dao.StudentDao;import com.model.entity.Student;import org.junit.jupiter.api.Test;import static org.junit.jupiter.api.Assertions.*;class TestDataAccess {    @Test    void testSelectMore() {        BaseDao
    
      baseDao = new BaseDao<>();        List
     
       students = baseDao.selectForMore(Student.class, "SELECT * FROM student");        assertTrue(students.size() > 0);        for (Student student : students) {            assertEquals("St", student.getName());        }    }    @Test    void testUpdate() {        BaseDao
      
        baseDao = new BaseDao<>();        Student student = new Student();        student.setName("X");        int updated = baseDao.update("UPDATE student SET name = ?", student.getName());        assertEquals(1, updated);    }}