java如何连接数据库executeUpdate()和executeQuery()

java如何连接数据库executeUpdate()和executeQuery()

目录UpdateInsertDeleteselect需要注意的点1.字符串的拼接必须在双引号的基础上被单引号套住2.在Bean类,默认的构造方法还与参数顺序有关3.构造方法的方法名就是类名....4.system.out.println 里打印加不加toString的区别5.sql语句里,双引号的里面套双引号,会有歧义execute()和executeUpdate()主要区别

executeUpdate

Update

//没有返回值

public void update(int count){

conn=DBUtil.getConn();

String sql="update counter set count=?";

try {

PreparedStatement ps = conn.prepareStatement(sql);

//传进去的

ps.setInt(1,count);

ps.executeUpdate();

} catch (SQLException e) {

e.printStackTrace();

}finally{

DBUtil.closeConn();

}

}

Insert

//没有返回值,参数是个字符串部门名称就ok了,因为id的话是自增

public void insert(String departmentname) {

conn = ConnectionFactory.getConnection();

String sql = "insert into department (departmentname) values(?)";

try {

PreparedStatement pstmt = conn.prepareStatement(sql);

pstmt.setString(1, departmentname);

pstmt.executeUpdate();

} catch (SQLException e) {

// TODO Auto-generated catch block

e.printStackTrace();

} finally {

ConnectionFactory.closeConnection();

}

}

//因为employeeid自增,所以不用设置

public void insert(Employee employee){

conn=ConnectionFactory.getConnectiondqOJOpz();

String sql="insert into employee"

+

"(employeename,username,password,phone,email,departmentid,status,role)" +

" values(?,?,?,?,?,?,?,?)";

try {

PreparedStatement pstmt = conn.prepareStatement(sql);

pstmt.setString(1,employee.getEmployeename());

pstmt.setString(2,employee.getUsername());

pstmt.setString(3,employee.getPassword() );

pstmt.setString(4,employee.getPhone() );

pstmt.setString(5,employee.getEmail());

pstmt.setInt(6,employee.getDepartmentid());

//注册成功后，默认为正在审核，status为0

pstmt.setString(7,"0");

//注册时，默认为员工角色，role值为2

pstmt.setString(8,"2");

pstmt.executeUpdate();

} catch (SQLException e) {

// TODO Auto-generated catch block

e.printStackTrace();

}finally{

ConnectionFactory.closeConnection();

}

}

Delete

//删除不用返回值

public void delete(int departmentid) {

conn = ConnectionFactory.getConnection();

String sql = "delete from department where departmentid=?;";

try {

PreparedStatement pstmt = conn.prepareStatement(sql);

pstmt.setInt(1, departmentid);

pstmt.executeUpdate();

} catch (SQLException e) {

// TODO Auto-generated catch block

e.printStackTrace();

} finally {

ConnectionFactory.closeConnection();

}

}

select

//返回int类型

public int select(){

int count=0;

conn=DBUtil.getConn();

String sql = "select * from counter";

try{

PreparedStatement ps = conn.PreparedStatement(sql);

ResultSet rs =ps.excuteQuery();

if(rs.next()){

count=rs.getInt("visitcount");

}

}catch{

}finally{

DBUtil.closeConn();

}

return count;

}

//返回部门集合

public List selectAll() {

conn = ConnectionFactory.getConnection();

// 新建一个集合departmentsList

List departmentsList = new ArrayList();

try {

Statement st = null;

String sql = "select * from department";

st = conn.createStatement();

ResultSet rs = st.executeQuery(sql);

Department department;

while (rs.next()) {

// 新建一个department来接收数据库的信息

department = new Department();

department.setDepartmentid(rs.getInt("departmentid"));

department.setDepartmentname(rs.getString("departmentname"));

departmentsList.add(department);

}

} catch (SQLException e) {

// TODO Auto-generated catch block

e.printStackTrace();

} finally {

ConnectionFactory.closeConnection();

}

// 返回集合

return departmentsList;

}

//返回员工

public List selectAllEmployee(){

conn=ConnectionFactory.getConnection();

List employeeslist=new ArrayList();

Employee employee=null;

try {

PreparedStatement st=null;

//只查询已注册且未审批 且 角色是员工的

String sql="select * from employee where role='2' and status='0'";

st = conn.prepareStatement(sql);

ResultSet rs =st.executeQuery(sql);

while(rs.next()){

employee=new Employee();

employee.setEmployeeid(rs.getInt("employeeid"));

employee.setEmployeename(rs.getString("employeename"));

employee.setUsername(rs.getString("username"));

employee.setPhone(rs.getString("phone"));

employee.setEmail(rs.getString("email"));

employee.setStatus(rs.getString("status"));

employee.setDepartmentid(rs.getInt("departmentid"));

employee.setPassword(rs.getString("password"));

employee.setRole(rs.getString("role"));

employeeslist.add(employee);

}

} catch (SQLException e) {

e.printStackTrace();

}finally{

//最后总要关闭连接

ConnectionFactory.closeConnection();

}

return employeeslist;

}

public Employee selectByNamePwd(String username, String pwd) {

Employee employee = null;

try {

//创建PreparedStatement对象

PreparedStatement st = null;

//查询语句

String sql = "select * from employee where username='" + username + "' and password='" + pwd + "'";

st = conn.prepareStatement(sql);

ResultSet rs = st.executeQuery(sql);

//判断结果集有无记录,http://如果有:则把内容取出来,变成一个employee对象,并且返回它

if (rs.next() == true) {

employee = new Employee();

employee.setEmployeeid(rs.getInt("employeeid"));

employee.setEmployeename(rs.getString("employeename"));

employee.setUsername(rs.getString("username"));

employee.setPhone(rs.getString("phone"));

employee.setEmail(rs.getString("email"));

employee.setStatus(rs.getString("status"));

employee.setDepartmentid(rs.getInt("status"));

employee.setPassword(rs.getString("password"));

employee.setRole(rs.getString("role"));

}

} catch (SQLException e) {

// TODO Auto-generated catch block

e.printStackTrace();

} finally {

ConnectionFactory.closeConnection();

}

return employee;

}

public Employee selectByUsername(String username){

conn=ConnectionFactory.getConnection();

Employee employee=null;

try {

PreparedStatement st=null;

String sql="select * from employee where username='"+username+"'";

st = conn.prepareStatement(sql);

ResultSet rs =st.executeQuery(sql);

if(rs.next()==true){

employee=new Employee();

employee.setEmployeeid(rs.getInt("employeeid"));

employee.setEmployeename(rs.getString("employeename"));

employee.setUsername(rs.getString("username"));

employee.setPhone(rs.getString("phone"));

employee.setEmail(rs.getString("email"));

employee.setStatus(rs.getString("status"));

employee.setDepartmentid(rs.getInt("status"));

employee.setPassword(rs.getString("password"));

employee.setRole(rs.getString("role"));

}

} catch (SQLException e) {

e.printStackTrace();

}finally{

ConnectionFactory.closeConnection();

}

return employee;

}

需要注意的点

1.字符串的拼接必须在双引号的基础上被单引号套住

上面有个小陷阱

如果加了

会正常执行，如果没有加，会因为字段不是字符串而报错.

结果集为空

2.在Bean类,默认的构造方法还与参数顺序有关

也就是说public Employee(String user,int id, String pwd){}

和 public Employee(int id,String user,String pwd){}  是不一样的构造方法

测试main方法里,插入的数据的类型顺序决定了调用哪个构造方法.

3.构造方法的方法名就是类名....

4.system.out.println 里打印加不加toString的区别

看起来没有区别(这个不敢肯定)

5.sql语句里,双引号的里面套双引号,会有歧义

会报错

应该在里面放单引号

execute()和exehttp://cuteUpdate()主要区别

execute()返回一个boolean类型值，true表示第一个结果是ResultSet对象，false表示第一个结果是没有结果的更新语句（insert，delete，update）。executeUpdate()返回一个int类型值，表示有几条数据受到了影响。

此外，execute()还可以通过getResultSet()获得执行语句后的结果；

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