怎么理解：ResultSet rs=statement.executeQuery(String sql)?

qinliu0425 2004-05-07 05:27:45

ResultSet 是一个接口，为什么却可以通过statement的方法返回一个实例？executeQuery是怎么生成ResultSet 实例的？

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切换为时间正序

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wuyaxlz 2004-05-07

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做程序要不求甚解！什么都问为什么你没法做好程序的。我老师教的

moke33 2004-05-07

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注意，返回的只是实例的引用，它们实现了ResultSet接口，当然可以指向它们了

cxz7531 2004-05-07

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你可以把mysql的jdbc驱动包mm.mysql-2.0.4-bin.jar 解开，就可以看到Connection,statement,ResultSet这几个接口的实现类

Arias 2004-05-07

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就是！本身驱动就有他们的实现方法！

dragon525 2004-05-07

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Connection,statement,ResultSet这些都是接口！

真正的实现得有jdbc的驱动来实现！

pleonheart 2004-05-07

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sun的JDBC只是规范了JDBC需要实现的方法，既是接口
所有的实现都是由数据库厂商完成，比如oracle的jar，db2的jar

package cn.com.dao.chivementdao; import java.sql.Connection; import java.sql.PreparedStatement; import java.sql.ResultSet; import java.sql.SQLException; import cn.com.util.DBConnection; import cn.com.util.DBSql; import cn.com.vo.chivementvo.ChivementVo; public class ExamDao { private Connection conn = DBConnection.getConnectionOracle(); private ChivementVo examVo; public ExamDao() { } public ExamDao(ChivementVo examVo) { super(); this.examVo = examVo; } /** * 全部查询 */ public Object[][] selectAll() { Object date[][] = null; int max = 0; int i = 0; PreparedStatement ps = null; ResultSet rs = null; try { ps = conn.prepareStatement(DBSql.SELECT_ALL); rs = ps.executeQuery(); // 得到列数 max = rs.getMetaData().getColumnCount(); date = new Object[getnumberAll(DBSql.SELECT_ALL_COUNT)][max]; while (rs.next()) { for (int j = 0; j < max; j++) { date[i][j] = rs.getObject(j + 1); } i++; } // rs.close(); // ps.close(); // conn.close(); } catch (SQLException e) { e.printStackTrace(); } return date; } /** * 根据学号查询 */ public Object[][] selectBySid() { Object date[][] = null; int max = 0; int i = 0; PreparedStatement ps = null; ResultSet rs = null; try { ps = conn.prepareStatement(DBSql.SELECT_BY_S_ID); ps.setInt(1, examVo.getS_id()); rs = ps.executeQuery(); // 得到列数 max = rs.getMetaData().getColumnCount(); date = new Object[getnumber(DBSql.SELECT_BY_S_ID_COUNT, examVo .getS_id())][max]; while (rs.next()) { for (int j = 0; j < max; j++) { date[i][j] = rs.getObject(j + 1); } i++; } // rs.close(); // ps.close(); // conn.close(); } catch (SQLException e) { e.printStackTrace(); } return date; } /** * 根据组号查询 */ public Object[][] selectByGid() { Object date[][] = null; int max = 0; int i = 0; PreparedStatement ps = null; ResultSet rs = null; try { ps = conn.prepareStatement(DBSql.SELECT_BY_G_ID); ps.setInt(1, examVo.getG_id()); rs = ps.executeQuery(); // 得到列数 max = rs.getMetaData().getColumnCount(); date = new Object[getnumber(DBSql.SELECT_BY_G_ID_COUNT, examVo .getG_id())][max]; while (rs.next()) { for (int j = 0; j < max; j++) { date[i][j] = rs.getObject(j + 1); } i++; } // rs.close(); // ps.close(); // conn.close(); } catch (SQLException e) { e.printStackTrace(); } return date; } /** * 根据课程号查询 */ public Object[][] selectByCid() { Object date[][] = null; int max = 0; int i = 0; PreparedStatement ps = null; ResultSet rs = null; try { ps = conn.prepareStatement(DBSql.SELECT_BY_C_ID); ps.setInt(1, examVo.getC_id()); rs = ps.executeQuery(); // 得到列数 max = rs.getMetaData().getColumnCount(); date = new Object[getnumber(DBSql.SELECT_BY_C_ID_COUNT, examVo .getC_id())][max]; while (rs.next()) { for (int j = 0; j < max; j++) { // System.out.println( examVo.getG_id()); date[i][j] = rs.getObject(j+1); } i++; } // rs.close(); // ps.close(); // conn.close(); } catch (SQLException e) { e.printStackTrace(); } return date; } /** * 根据姓名模糊查询 * * @return */ public Object[][] selectByName() { Object date[][] = null; int max = 0; int i = 0; PreparedStatement ps = null; ResultSet rs = null; try { ps = conn.prepareStatement(DBSql.SELECT_BY_S_NAME); ps.setString(1, examVo.getS_name()); ps.setString(2, "%" + examVo.getS_name() + "%"); ps.setString(3, "%" + examVo.getS_name()); ps.setString(4, examVo.getS_name() + "%"); rs = ps.executeQuery(); // 得到列数 max = rs.getMetaData().getColumnCount(); date = new Object[getnumberByName(DBSql.SELECT_BY_S_NAME_COUNT, examVo.getS_name())][max]; while (rs.next()) { for (int j = 0; j < max; j++) { date[i][j] = rs.getObject(j + 1); } i++; } } catch (SQLException e) { e.printStackTrace(); } return date; } /** * 根据课程名称模糊查询 * * @return */ public Object[][] selectByClassName() { Object date[][] = null; int max = 0; int i = 0; PreparedStatement ps = null; ResultSet rs = null; try { ps = conn.prepareStatement(DBSql.SELECT_BY_CLASS_NAME); ps.setString(1, examVo.getClass_name()); ps.setString(2, "%" + examVo.getClass_name() + "%"); ps.setString(3, "%" + examVo.getClass_name()); ps.setString(4, examVo.getClass_name() + "%"); rs = ps.executeQuery(); // 得到列数 max = rs.getMetaData().getColumnCount(); date = new Object[getnumberByName(DBSql.SELECT_BY_CLASS_COUNT, examVo.getClass_name())][max]; while (rs.next()) { for (int j = 0; j < max; j++) { date[i][j] = rs.getObject(j + 1); } i++; } } catch (SQLException e) { e.printStackTrace(); } return date; } /** * 修改选中学生的成绩 * */ public void updatSelectClass() { PreparedStatement ps = null; ResultSet rs = null; try { ps = conn.prepareStatement(DBSql.UPDATE_EXAM_BY_STUID); ps.setInt(1, examVo.getClassExamChivement()); ps.setInt(2, examVo.getS_id()); ps.setInt(3, examVo.getC_id()); ps.executeUpdate(); } catch (SQLException e) { e.printStackTrace(); } } /** * 得到所有课程号和课程名 * * @return */ public String[] getClassNoName() { String[] classNoName = null; PreparedStatement ps = null; ResultSet rs = null; int j = 0; try { int i = getnumberAll(DBSql.SELECT_CLASS_NAME_COUNT); classNoName = new String[i + i]; ps = conn.prepareStatement(DBSql.SELECT_CLASS_NAME); rs = ps.executeQuery(); while (rs.next()) { classNoName[j] = rs.getString(1); classNoName[j + i] = rs.getString(2); j++; } } catch (SQLException e) { e.printStackTrace(); } return classNoName; } /** * 根据科目修改成绩查询学号姓名成绩 * */ public void SelectClassStuName() { int i = 0; PreparedStatement ps = null; ResultSet rs = null; int j = getnumberBySelectClassName( DBSql.SELECT_CLASS_STU_SNO_SNAME_EXAM_COUNT, examVo.getC_id()); int[] sNum = new int[j]; String[] sName = new String[j]; int[] classExam = new int[j]; try { ps = conn.prepareStatement(DBSql.SELECT_CLASS_STU_SNO_SNAME_EXAM); ps.setInt(1, examVo.getC_id()); rs = ps.executeQuery(); while (rs.next()) { sNum[i] = rs.getInt(1); sName[i] = rs.getString(2); classExam[i] = rs.getInt(3); i++; } } catch (SQLException e) { e.printStackTrace(); } examVo.setSid(sNum); examVo.setSname(sName); examVo.setClassExam(classExam); } /** * 根据科目修改成绩查询学号姓名成绩后修改成绩 * */ public void UpdateClassStuName() { // int i = 0; PreparedStatement ps = null; ResultSet rs = null; int j = getnumberBySelectClassName( DBSql.SELECT_CLASS_STU_SNO_SNAME_EXAM_COUNT, examVo.getC_id()); try { ps = conn.prepareStatement(DBSql.UPDATE_CHIVEMENT_BY_CLASS); for(int i =0;iexecuteUpdate(); } } catch (SQLException e) { e.printStackTrace(); } } /** * 全部查询获得行数 * * @return */ public int getnumberAll(String str) { int number = 0; PreparedStatement ps = null; ResultSet rs = null; try { ps = conn.prepareStatement(str); rs = ps.executeQuery(); rs.next(); number = rs.getInt(1); // rs.close(); // ps.close(); // conn.close(); } catch (SQLException e) { e.printStackTrace(); } return number; } /** * 根据学号根据组号根据课程号查询获得行数 * * @return */ public int getnumber(String str, int i) { int number = 0; PreparedStatement ps = null; ResultSet rs = null; try { ps = conn.prepareStatement(str); ps.setInt(1, i); rs = ps.executeQuery(); rs.next(); number = rs.getInt(1); // rs.close(); // ps.close(); // conn.close(); } catch (SQLException e) { e.printStackTrace(); } return number; } /** * 根据姓名课程名查询获得行数 * */ public int getnumberByName(String str, String i) { int number = 0; PreparedStatement ps = null; ResultSet rs = null; try { ps = conn.prepareStatement(str); ps.setString(1, i); ps.setString(2, "%" + i + "%"); ps.setString(3, "%" + i); ps.setString(4, i + "%"); rs = ps.executeQuery(); rs.next(); number = rs.getInt(1); } catch (SQLException e) { e.printStackTrace(); } return number; } // /** // * 根据课程名查询获得行数 // * // */ // // public int getnumberByClassName(String str, String i) { // int number = 0; // PreparedStatement ps = null; // ResultSet rs = null; // try { // ps = conn.prepareStatement(str); // ps.setString(1, i); // ps.setString(2, "%" + i + "%"); // ps.setString(3, "%" + i); // ps.setString(4, i + "%"); // rs = ps.executeQuery(); // rs.next(); // number = rs.getInt(1); // } catch (SQLException e) { // e.printStackTrace(); // } // return number; // } /** * * 根据课程名修改成绩获得行数 * * @param str * @param i * @return */ public int getnumberBySelectClassName(String str, int i) { int number = 0; PreparedStatement ps = null; ResultSet rs = null; try { ps = conn.prepareStatement(str); ps.setInt(1, i); rs = ps.executeQuery(); rs.next(); number = rs.getInt(1); } catch (SQLException e) { e.printStackTrace(); } return number; } }

MySQL官方提供的驱动包 mysql-connector-java-5.1.30.zip

当需要查询的语句带有参数时执行预编译后 **1.原因：**不能在下面这条语句中插入sql值 **2.理由：**因为预编译已经改变了sql语句，向语句中的问号？插入了值，如果在rs语句中插入sql，会导致执行的是原来带问号的sql语句。也就是说预编译的sql语句没有被执行，mysql不能执行带问号的sql语句，所以报错 ResultSet rs = pstm.executeQuery(sql); ...

JAVA ResultSetrs=stmt.executeQuery(sql);//查询返回的结果集不管是否查到，rs都不是null,那么问题是怎么判断查找不到来执行一个提示“账号或者密码错误”呢？ rs.next()==null ResultSet rs = stmt.executeQuery(sql); //查询返回的结果集 ...

web编程 rs=stmt.executeQuery(sql);报错 type Exception report message An exception occurred processing JSP page /sql.jsp at line 22 description The server encountered an internal error that prevented it from fulfilling this request. exception org.apache.jasp

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