DBUtils

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，ResultSetHandlerrsh,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)，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。

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示例：采用Druid和dbutils实现对Dept的CRUD

• 第一步：Dept.java：Dept源代码

• 第二步：新建项目，加入Maven依赖：

  <dependency>
    <groupId>commons-dbutilsgroupId>
    <artifactId>commons-dbutilsartifactId>
    <version>1.7version>
  dependency>
  <dependency>
      <groupId>com.alibabagroupId>
      <artifactId>druidartifactId>
      <version>1.1.17version>
  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