DBUtils使用详解 #yyds干货盘点#

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DBUtils

简介

DBUtils是Java编程中的数据库操作实用工具,小巧简单实用。DBUtils封装了对JDBC的操作,简化了JDBC操作,可以减少60%以上的代码。

DBUtils三个核心功能介绍

  • QueryRunner:核心类提供对sql语句操作的API
    • QueryRunner(DataSourcr ds):提供数据源(连接池),DbUtils底层自动维护连接connection
    • update(String sql,Obj...params):执行更新操作
    • query(String sql,ResultSetHandler<T>rsh,Object...panrams):执行查询操作
  • ResultSetHandler:结果集处理类,用于定义select操作后,怎样封装结果集
    • ArrayHandler:把查询结果集中的第一行数据放到一个数组中。适合取1条记录。
    • ArrayListHandler:将查询的结果的每一行数据都放到一个数组中,然后再将数组放到集合List中。适合取多条记录。
    • BeanHandler:将结果集中的第一行数据封装到一个对应的JavaBean实例中
    • BeanListHandler:将结果集中的每一行数据都封装到一个对应的JavaBean实例中,然后再将这些对象存放到List里。
    • MapHandler:将结果集中的第一行数据封装到一个Map里,key是列名,value就是对应的值。
    • MapListHandler:将查询的结果的每一行存入到一个map中,键为列名,值为各列值;然后再将map存入list中
    • ColumnListHandler:将结果集中某一列的数据存放到List中。
    • KeyedHandler(name):将结果集中的每一行数据都封装到一个Map里(List<Map>),再把这些map再存到一个map里,其key为指定的列。
    • ScalarHandler:将结果集第一行的某一列放到某个对象中。//重点
  • DBUtils:工具类,定义了关闭资源与事务处理的方法。

示例:采用Druid和dbutils实现对Dept的CRUD

  • 第一步:Dept.java:<a rel="nofollow" href="https://blog.csdn.net/lianghecai52171314/article/details/101469279">Dept源代码</a>;
  • 第二步:新建项目,加入Maven依赖:

    <dependency>
      <groupId>commons-dbutils</groupId>
      <artifactId>commons-dbutils</artifactId>
      <version>1.7</version>
    </dependency>
    <dependency>
        <groupId>com.alibaba</groupId>
        <artifactId>druid</artifactId>
        <version>1.1.17</version>
    </dependency>
  • 第二步:在resources目录下创建mysql.properties,代码如下:

    driverClassName=com.mysql.cj.jdbc.Driver
    url=jdbc:mysql://localhost:3306/test?useSSL=false&serverTimezone=UTC&user=root&password=&useUnicode=true&characterEncoding=UTF8&autoReconnect=true&failOverReadOnly=false
    username=root
    password=root
    
    filters=stat
    initialSize=2
    maxActive=300
    maxWait=60000
    timeBetweenEvictionRunsMillis=60000
    minEvictableIdleTimeMillis=300000
    validationQuery=SELECT 1
    testWhileIdle=true
    testOnBorrow=false
    testOnReturn=false
    poolPreparedStatements=false
    maxPoolPreparedStatementPerConnectionSize=200
  • 第三步:创建数据库连接工具类:

    public class DBUtil 
        private static final ThreadLocal<Connection> threadLocal = new ThreadLocal<>();
        private static DataSource dataSource = null;
    
        private DBUtil() 
        
    
        static     //配置文件加载,只执行一次
            try (InputStream is = DBUtil.class.getResourceAsStream("/mysql.properties");) 
                Properties properties = new Properties();
                properties.load(is);
                dataSource = DruidDataSourceFactory.createDataSource(properties);
             catch (Exception e1) 
                throw new RuntimeException("读取配置文件异常", e1);
            
        
    
        public static Connection getConnection()     //获取连接
            Connection conn = null;
            try 
                conn = threadLocal.get();   //从当前线程获得 conn
                if (conn == null || conn.isClosed()) 
                    conn = dataSource.getConnection();
                    threadLocal.set(conn);
                
             catch (Exception e) 
                throw new RuntimeException("连接数据库异常", e);
            
            return conn;
        
    
        public static QueryRunner getQueryRunner() 
            return new QueryRunner(dataSource);
        
    
        public static void release(Connection conn) 
            try  // 建议采用这种形式来释放资源,因为finally里面的一定会被释放
                if (conn != null) 
                    conn.close();
                
             catch (SQLException e) 
                e.printStackTrace();
            
        
    
  • 第四步:测试事务
    public static void main(String[] args) 
        Connection conn = getConnection();
        try 
            conn.setAutoCommit(false); // 设置事务提交为手动
            String sql = "insert into tb_dept (dname,loc) values(?,?)";
            QueryRunner queryRunner = getQueryRunner();
            queryRunner.update(conn, sql, "aa", "aaaaa");
            System.out.println(3 / 0);
            queryRunner.update(sql, "bb", "bbbbbbbbbb");
            conn.commit();
         catch (SQLException e) 
            e.printStackTrace();
            try 
                conn.rollback();
             catch (SQLException ex) 
                ex.printStackTrace();
            
         finally 
            release(conn);
        
    
  • 第五步:DeptDaoImpl.java

    public class DeptDaoImpl 
        private QueryRunner queryRunner = DBUtil.getQueryRunner();
    
        public int insertDept(Dept dept) throws SQLException 
            String sql = "insert into tb_dept (deptno, dname, loc) values (?, ?, ?)";
            return queryRunner.update(sql, dept.getDeptno(), dept.getDname(), dept.getLoc());
        
    
        public int batchInsertDept(List<Dept> deptList) throws SQLException 
            Object[][] params = new Object[deptList.size()][3];
    
            for (int i = 0; i < params.length; i++) 
                Dept dept = deptList.get(i);
                params[i][0] = dept.getDeptno();
                params[i][1] = dept.getDname();
                params[i][2] = dept.getLoc();
            
    
            StringBuilder wenHao = new StringBuilder();
            for (int i = 0; i < params[0].length; i++) 
                wenHao.append("?,");
            
            String sql = "insert into tb_dept values(" + wenHao.deleteCharAt(wenHao.length() - 1) + ")";
    
            queryRunner.batch(sql, params);
            return 1;  // 如果不抛出异常,就返回1,表示删除成功
        
    
        public int deleteDeptByDeptno(Byte deptno) throws SQLException 
            String sql = "delete from tb_dept where deptno = ?";
            return queryRunner.update(sql, deptno);
        
    
        public int deleteDeptByCondition(Dept dept) throws SQLException 
            List<Object> paramValueList = new ArrayList<>();
            StringBuffer paramBuf = new StringBuffer("1=1 ");
    
            if (dept.getDeptno() != null) 
                paramBuf.append("and deptno= ? ");
                paramValueList.add(dept.getDeptno());
            
            if (dept.getDname() != null) 
                paramBuf.append("and dname= ? ");
                paramValueList.add(dept.getDname());
            
            if (dept.getLoc() != null) 
                paramBuf.append("and loc= ? ");
                paramValueList.add(dept.getLoc());
            
    
            String sql = "delete from tb_dept where " + paramBuf.substring(0, paramBuf.length() - 3);
            return queryRunner.update(sql, paramValueList.toArray());
        
    
        public int batchDeleteDeptByDeptnos(String deptnos) throws SQLException 
            String[] split = deptnos.split(",");
            Object[][] params = new Object[1][];
    
            StringBuilder wenHao = new StringBuilder();
            for (int i = 0; i < split.length; i++) 
                wenHao.append("?,");
            
            params[0] = split;
    
            String sql = "delete from tb_dept where deptno in (" + wenHao.deleteCharAt(wenHao.length() - 1) + ")";
    
            queryRunner.batch(sql, params);
            return 1;  // 如果不抛出异常,就返回1,表示删除成功
        
    
        public int updateDept(Dept dept) throws SQLException 
            String sql = "update tb_dept set dname= ? ,loc= ? where deptno = ?";
            return queryRunner.update(sql, dept.getDname(), dept.getLoc(), dept.getDeptno());
        
    
        public long selectCount() throws SQLException 
            String sql = "select count(*) from tb_dept";
            // ScalarHandler:将查询的结果的第一行的某一列放到一个对象中;精确定位到某个值
            Long query = queryRunner.query(sql, new ScalarHandler<Long>());
            return query.intValue();
        
    
        public long selectCountByCondition(Dept dept) throws SQLException 
            List<Object> paramValueList = new ArrayList<>();
            StringBuffer paramBuf = new StringBuffer("1=1 ");
    
            if (dept.getDeptno() != null) 
                paramBuf.append("and deptno= ? ");
                paramValueList.add(dept.getDeptno());
            
            if (dept.getDname() != null) 
                paramBuf.append("and dname= ? ");
                paramValueList.add(dept.getDname());
            
            if (dept.getLoc() != null) 
                paramBuf.append("and loc= ? ");
                paramValueList.add(dept.getLoc());
            
    
            String sql = "select count(*) from tb_dept where " + paramBuf.substring(0, paramBuf.length() - 3);
            Long query = queryRunner.query(sql, new ScalarHandler<Long>(), paramValueList.toArray());
            return query.intValue();
        
    
        public Dept selectDeptByDeptno(Byte deptno) throws SQLException 
            String sql = "select deptno as deptno, dname as dname, loc as loc from tb_dept where  deptno = ?";
            return queryRunner.query(sql, new BeanHandler<>(Dept.class), deptno);
        
    
        public List<Dept> selectAllDept() throws SQLException 
            String sql = "select deptno as deptno, dname as dname, loc as loc from tb_dept";
            return queryRunner.query(sql, new BeanListHandler<>(Dept.class));
        
    
        public List<Dept> selectDeptByCondition(Dept dept) throws SQLException 
            List<Object> paramValueList = new ArrayList<>();
            StringBuffer paramBuf = new StringBuffer("1=1 ");
    
            if (dept.getDeptno() != null) 
                paramBuf.append("and deptno= ? ");
                paramValueList.add(dept.getDeptno());
            
            if (dept.getDname() != null) 
                paramBuf.append("and dname= ? ");
                paramValueList.add(dept.getDname());
            
            if (dept.getLoc() != null) 
                paramBuf.append("and loc= ? ");
                paramValueList.add(dept.getLoc());
            
    
            String sql = "select deptno as deptno, dname as dname, loc as loc  from tb_dept where " + paramBuf.substring(0, paramBuf.length() - 3);
            return queryRunner.query(sql, new BeanListHandler<>(Dept.class), paramValueList.toArray());
        
    
        public List<Dept> selectDeptWithPagination(int page, int rows) throws SQLException 
            String sql = "select deptno as deptno, dname as dname, loc as loc from tb_dept limit ?, ?";
            return queryRunner.query(sql, new BeanListHandler<>(Dept.class), (page - 1) * rows, rows);
        
    
        public List<Dept> selectDeptWithPaginationByCondition(int page, int rows, Dept dept) throws SQLException 
            List<Object> paramValueList = new ArrayList<>();
            StringBuffer paramBuf = new StringBuffer("1=1 ");
    
            if (dept.getDeptno() != null) 
                paramBuf.append("and deptno= ? ");
                paramValueList.add(dept.getDeptno());
            
            if (dept.getDname() != null) 
                paramBuf.append("and dname= ? ");
                paramValueList.add(dept.getDname());
            
            if (dept.getLoc() != null) 
                paramBuf.append("and loc= ? ");
                paramValueList.add(dept.getLoc());
            
    
            String sql = "select deptno as deptno, dname as dname, loc as loc  from tb_dept where " + paramBuf.substring(0, paramBuf.length() - 3) + " limit ?, ?";
    
            paramValueList.add((page - 1) * rows);
            paramValueList.add(rows);
            return queryRunner.query(sql, new BeanListHandler<>(Dept.class), paramValueList.toArray());
        
    

    动态SQL与静态SQL

    SQL 语句从编译和运行的角度可以分为静态 SQL和 动态 SQL,所谓SQL的动态和静态,是指SQL语句在何时被编译和执行。

这两种 SQL 在使用方式、运行机制和性能表现等方面各有特点 :

  • 静态 SQL:静态 SQL 语句一般用于嵌入式 SQL 应用中,在程序运行前,SQL 语句在编程时候必须是确定好的,例如 SQL 语句中涉及的列名和表名必须是存在的。静态 SQL 语句的编译是在应用程序运行前进行的,编译的结果会存储在数据库内部。而后程序运行时,数据库将直接执行编译好的 SQL 语句,降低运行时的开销。
  • 动态 SQL:动态 SQL 语句是在应用程序运行时被编译和执行的,例如,使用 DB2 的交互式工具 CLP 访问数据库时,用户输入的 SQL 语句是不确定的,因此 SQL 语句只能被动态地编译。动态 SQL 的应用较多,常见的 CLI 和 JDBC 应用程序都使用动态 SQL。

静态sql的存取路径是在运行前就确定好的,而动态sql的存取路径是在运行时动态生成的。

注意:在SQL中如果某些参数没有确定,如"select * from t1 where c1>? and c2<?",这种语句是静态SQL,不是动态SQL,虽然个别参数的值不知道,但整个SQL的结构已经确定,数据库是可以将它编译的,在执行阶段只需将个别参数的值补充进来即可。

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