第一步：事务是自动提交的我们 手动关闭自动提交
conn.setAutoCommit(false);
第二步：如果没有异常就提交事务
conn.commit();
第三步：如果抛出异常 我们我们就让他回滚
conn.rollback();

import java.io.FileNotFoundException;
import java.io.FileReader;
import java.io.IOException;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.SQLException;
import java.util.Properties;

/**
 * @author zss
 */
public class TransferAccount {
    public static void main(String[] args) throws IOException, ClassNotFoundException, SQLException {
        Properties properties=new Properties();
        properties.load(new FileReader("src\\Information.properties"));
        String jdbc= properties.getProperty("jdbcJar");
        String url= properties.getProperty("url");
        String password= properties.getProperty("password");
        String user= properties.getProperty("user");
        Class.forName(jdbc);
        Connection connection= DriverManager.getConnection(url,user,password);
        String sql1="update user_table set balance=balance-100 where user=(?) ";
        String sql2="update user_table set balance=balance+100 where user=(?) ";
        PreparedStatement preparedStatement1= connection.prepareStatement(sql1);
        PreparedStatement preparedStatement2= connection.prepareStatement(sql2);
        preparedStatement1.setString(1,"AA");
        preparedStatement2.setString(1,"BB");
        //AA转账
        preparedStatement1.executeUpdate();
        //发生故障
        System.out.println(10/0);
        //BB接受账单
        preparedStatement2.executeUpdate();
        preparedStatement1.close();
        preparedStatement2.close();
        connection.close();
    }
}

import java.io.FileNotFoundException;
import java.io.FileReader;
import java.io.IOException;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.SQLException;
import java.util.Properties;

/**
 * @author zss
 */
public class TransferAccount {
    public static void main(String[] args) throws IOException, ClassNotFoundException, SQLException {
        Properties properties=new Properties();
        properties.load(new FileReader("src\\Information.properties"));
        String jdbc= properties.getProperty("jdbcJar");
        String url= properties.getProperty("url");
        String password= properties.getProperty("password");
        String user= properties.getProperty("user");
        Class.forName(jdbc);
        Connection connection= DriverManager.getConnection(url,user,password);
        connection.setAutoCommit(false);
        String sql1="update user_table set balance=balance-100 where user=(?) ";
        String sql2="update user_table set balance=balance+100 where user=(?) ";
        PreparedStatement preparedStatement1= connection.prepareStatement(sql1);
        PreparedStatement preparedStatement2= connection.prepareStatement(sql2);
        preparedStatement1.setString(1,"AA");
        preparedStatement2.setString(1,"BB");
        try {


        //AA转账
        preparedStatement1.executeUpdate();
        //发生故障
        //System.out.println(10/0);
        //BB接受账单
        preparedStatement2.executeUpdate();}catch (ArithmeticException arithmeticException){
            System.out.println("交易发生异常，事务进行回滚");
            connection.rollback();
        }
        //如果没有发生异常则提交数据
        connection.commit();
        preparedStatement1.close();
        preparedStatement2.close();
        connection.close();
    }
}

Driver driver=new Driver();
DriverManager.registerDriver(driver);

Class.forName("com.mysql.jdbc.Driver");

//获取链接
Connection connection=DriverManager.getConnection(url,user,password);
//获取数据库操作对象
Statement  statement=connection.createStatement();

//获取链接
Properties properties=new Properties();
properties.load(new FileReader("src/Mysql.properties"));
String url= properties.getProperty("url");
String user= properties.getProperty("user");
String passWord= properties.getProperty("passWord");
Connection connection=DriverManager.getConnection(url,user,passWord);
//获得数据库的操作对象
Statement statement=connection.createStatement();

//定义操作语句
String insertSql="insert into usersimple values ('张山峰',12,'高管')";
String insertSql1="insert into usersimple values ('丽丽',25,'职员')";
String updateSql="update usersimple set 职位='职员' where 职位='高管' ";
String deleteSql="delete from usersimple where 用户名称='丽丽' ";

//结果判断
int count=0;
count=statement.executeUpdate(insertSql);
System.out.println(count==1?"插入成功":"插入失败");
count=statement.executeUpdate(insertSql1);
System.out.println(count==1?"插入成功":"插入失败");
count=statement.executeUpdate(updateSql);
System.out.println(count==1?"更新成功":"更新失败");
count=statement.executeUpdate(deleteSql);
System.out.println(count==1?"删除成功":"删除失败");

String selectSql="select * from usersimple";
ResultSet resultSet=statement.executeQuery(selectSql);
while (resultSet.next()){
    String userName=resultSet.getString("用户名称");
    int age=resultSet.getInt("年龄");
    String position=resultSet.getString("职位");
    System.out.println(userName+age+position);

finally {
            if (resultSet!=null){try{
                resultSet.close();

            }
            catch (SQLException e) {
                e.printStackTrace();}}
            try {
                if (statement!=null) {
                    statement.close();
                }
            } catch (SQLException e) {
                e.printStackTrace();
            }
            try{
                if (connection!=null){
                    connection.close();
                }
            }catch (SQLException e){
                e.printStackTrace();
            }
        }

package com.zss.jdbc;

import com.mysql.jdbc.Driver;

import java.io.FileNotFoundException;
import java.io.FileReader;
import java.io.IOException;
import java.sql.*;
import java.util.Properties;

/**
 * @author zss
 */
public class JdbcLearn {
    public static void main(String[] args) throws ClassNotFoundException, IOException, SQLException {
        /*Driver driver=new Driver();
        DriverManager.registerDriver(driver);*/
        Class cla=Class.forName("com.mysql.jdbc.Driver");
        //获取链接
        Properties properties=new Properties();
        properties.load(new FileReader("src/Mysql.properties"));
        String url= properties.getProperty("url");
        String user= properties.getProperty("user");
        String passWord= properties.getProperty("passWord");
        Connection connection=DriverManager.getConnection(url,user,passWord);
        //获得数据库的操作对象
        Statement statement=connection.createStatement();
        //定义操作语句
        String insertSql="insert into usersimple values ('张山峰',12,'高管')";
        String insertSql1="insert into usersimple values ('丽丽',25,'职员')";
        String updateSql="update usersimple set 职位='职员' where 职位='高管' ";
        String deleteSql="delete from usersimple where 用户名称='丽丽' ";
        //结果判断
        int count=0;
        count=statement.executeUpdate(insertSql);
        System.out.println(count==1?"插入成功":"插入失败");
        count=statement.executeUpdate(insertSql1);
        System.out.println(count==1?"插入成功":"插入失败");
        count=statement.executeUpdate(updateSql);
        System.out.println(count==1?"更新成功":"更新失败");
        count=statement.executeUpdate(deleteSql);
        System.out.println(count==1?"删除成功":"删除失败");

        String selectSql="select * from usersimple";
        ResultSet resultSet=statement.executeQuery(selectSql);
        while (resultSet.next()){
            String userName=resultSet.getString("用户名称");
            int age=resultSet.getInt("年龄");
            String position=resultSet.getString("职位");
            System.out.println(userName+age+position);
        }
        resultSet.close();
        statement.close();
        connection.close();
    }
}

package com.zss.jdbc;

import java.sql.*;
import java.util.HashMap;
import java.util.Map;
import java.util.Scanner;
/**
 * @author 张硕硕
 */
public class test {
    public static void main(String [] args){
        Map<String,String> haha= test.initUi();
        System.out.println(test.login(haha)?"登陆成功":"登陆失败");
    }
    private  static Map<String ,String > initUi(){
        Scanner scanner=new Scanner(System.in);
        System.out.println("请输入您的用户名");
        String userName=scanner.nextLine();
        System.out.println("请输入您的登录密码");
        String password=scanner.nextLine();
        Map<String,String> userInformation=new HashMap<>();
        userInformation.put("username",userName);
        userInformation.put("password",password);
        return userInformation;
    }
    private  static boolean login(Map<String,String> userInformation){
        boolean loginY=false;
        Connection connection=null;
        Statement statement=null;
        ResultSet resultset=null;
        try{
            Class.forName("com.mysql.cj.jdbc.Driver");
            connection= DriverManager.getConnection("jdbc:mysql://localhost:3306/userinformation","root","200101");
            statement=connection.createStatement();
            String sql="select * from user where 用户名= '"+userInformation.get("username")+"'and 密码= '"+userInformation.get("password")+"'";
            resultset=statement.executeQuery(sql);
            if (resultset.next()){loginY=true;}
        }
        catch (Exception e){e.printStackTrace();}

        finally {
            if (resultset!=null){try{resultset.close();}catch (Exception e){e.printStackTrace();}}
            if (statement!=null){try{statement.close();}catch (Exception e){e.printStackTrace();}}
            if (connection!=null){try{connection.close();}catch(Exception e){e.printStackTrace();}}

        }
        return loginY;
    }

}

package com.zss.jdbc;

import java.sql.*;
import java.util.HashMap;
import java.util.Map;
import java.util.Scanner;
/**
 * @author 张硕硕
 */
public class test {
    public static void main(String [] args){
        Map<String,String> haha= test.initUi();
        System.out.println(test.login(haha)?"登陆成功":"登陆失败");
    }
    private  static Map<String ,String > initUi(){
        Scanner scanner=new Scanner(System.in);
        System.out.println("请输入您的用户名");
        String userName=scanner.nextLine();
        System.out.println("请输入您的登录密码");
        String password=scanner.nextLine();
        Map<String,String> userInformation=new HashMap<>();
        userInformation.put("username",userName);
        userInformation.put("password",password);
        return userInformation;
    }
    private  static boolean login(Map<String,String> userInformation){
        boolean loginY=false;
        Connection connection=null;
        PreparedStatement preparedStatement=null;
        ResultSet resultset=null;
        try{
            Class.forName("com.mysql.cj.jdbc.Driver");
            connection= DriverManager.getConnection("jdbc:mysql://localhost:3306/userinformation","root","200101");
            String sql="select * from user where 用户名= ? and 密码= ? ";
            preparedStatement=connection.prepareStatement(sql);
            preparedStatement.setString(1,userInformation.get("username"));
            preparedStatement.setString(2,userInformation.get("password"));
            resultset= preparedStatement.executeQuery();
            if (resultset.next()){loginY=true;}
        }
        catch (Exception e){e.printStackTrace();}

        finally {
            if (resultset!=null){try{resultset.close();}catch (Exception e){e.printStackTrace();}}
            if (preparedStatement!=null){try{preparedStatement.close();}catch (Exception e){e.printStackTrace();}}
            if (connection!=null){try{connection.close();}catch(Exception e){e.printStackTrace();}}

        }
        return loginY;
    }

}

class ListNode{
    //节点的值
    int val;
    //下一个节点
    ListNode next;
    //无参构造器
    public ListNode(){

    }
    //节点的构造函数
    public ListNode(int val){
        this.val=val;
    }
    public ListNode(int val,ListNode next){
        this.val=val;
        this.next=next;
    }
}

public ListNode removeElements(ListNode head, int val) {

    while ( head!=null&&head.val==val ){
        head=head.next;
    }
    if(head==null){
        return head;
    }
        ListNode preNode=head;
        ListNode curNode=head.next;
        while (curNode != null) {
            if (curNode.val==val){
                preNode.next=curNode.next;
            }else {
                preNode=curNode;
            }
            curNode=curNode.next;
        }

    return head;
}

public ListNode removeElements(ListNode head, int val) {
    if(head==null){
        return head;
    }

        ListNode dummy=new ListNode(-1,head);
        ListNode preNode=dummy;
        ListNode curNode=head;
        while (curNode != null) {
            if (curNode.val==val){
                preNode.next=curNode.next;
            }else {
                preNode=curNode;
            }
            curNode=curNode.next;
        }
//在这里返回dummy.next;是因为上面的方法中头节点在一直改变，head所代表的节点在一直发生改变，在这里可能原来的head.val==val，head已经消失了
    return dummy.next;
}

public ListNode getIntersectionNode(ListNode headA, ListNode headB) {
    ListNode tempA = headA;

    //用于存储相交的节点
    while (tempA != null) {
        ListNode tempB = headB;
        while (tempB != null) {
            if (tempA == tempB) {
                return tempA;
            } else {
                if (tempB.next != null) {
                    tempB = tempB.next;
                } else {
                    break;
                }
            }
        }
        if (tempA.next != null) {
            tempA = tempA.next;
        } else {
            return null;
        }
    }
    return null;
}

public ListNode getIntersectionNode(ListNode headA, ListNode headB) {
    HashSet<ListNode> hashSet = new HashSet<>();
    ListNode tempA = headA;
    while (tempA != null) {
        hashSet.add(tempA);
        if (tempA.next != null) {
            tempA = tempA.next;
        } else {
            break;
        }
    }
    ListNode tempB = headB;
    while (tempB != null) {
        if (!hashSet.add(tempB)) {
            return tempB;
        } else {
            if (tempB.next != null) {
                tempB = tempB.next;
            }else {
                break;
            }
        }
    }
    return null;
}

public ListNode getIntersectionNode(ListNode headA, ListNode headB) {
        /*
        总体思路:双指针
        headA=[a1,a2,...,an]与headB=[b1,b2,...,bn]
        pA在a1出发,pB在b1出发;当pA到达A链表末尾null就到B开头处重新开始;pB同理
        最后两个指针相遇时就是相交的地方
         */
        ListNode pA = headA, pB = headB;
        while (pA != pB) {
            // A指针与B一路往下走,走完了就去另一个链表的头结点,直至相遇
            // 这里注意不能用pA.next作为判断,因为遇到空链表会发生空指针异常
            // 这里就算有其中一个链表为空或者没相交的也成立(最后为null)
            pA = pA == null ? headB : pA.next;
            pB = pB == null ? headA : pB.next;
        }
        // pA==pB
        return pA;
    }

/**
 * Definition for singly-linked list.
 * class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) {
 *         val = x;
 *         next = null;
 *     }
 * }
 */
public class Solution {
    public ListNode detectCycle(ListNode head) {
        HashSet<ListNode> listNodes=new HashSet<>();

        ListNode temp=head;
        while (temp!=null){
            if (!listNodes.add(temp)){
                return temp;
            }else {
                temp=temp.next;
            }

        }
        return null;
    }
} 

public class Solution {
    public ListNode detectCycle(ListNode head) {
        if (head == null) {
            return null;
        }
        ListNode slow = head, fast = head;
        while (fast != null) {
            slow = slow.next;
            if (fast.next != null) {
                fast = fast.next.next;
            } else {
                return null;
            }
            if (fast == slow) {
                ListNode ptr = head;
                while (ptr != slow) {
                    ptr = ptr.next;
                    slow = slow.next;
                }
                return ptr;
            }
        }
        return null;
    }
}

@WebServlet("/axios01.do")
public class Axios01Servlet extends HttpServlet {
    @Override
    protected void service(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        request.setCharacterEncoding("utf-8");

        String uname = request.getParameter("uname");
        String pwd = request.getParameter("pwd");

        System.out.println("uname = " + uname);
        System.out.println("pwd = " + pwd);

        response.setCharacterEncoding("utf-8");
        response.setContentType("text/html;charset=utf-8");
        PrintWriter out = response.getWriter();
        out.write(uname+"_"+pwd);

        throw new NullPointerException("这里故意抛出一个空指针异常....");
    }
}

@WebServlet("/axios02.do")
public class Axios02Servlet extends HttpServlet {
    @Override
    protected void service(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

        StringBuffer stringBuffer = new StringBuffer("");
        //获得对应的读取流
        BufferedReader bufferedReader = request.getReader();
        String str = null ;
        while((str=bufferedReader.readLine())!=null){
            //将读到的数据进行追加
            stringBuffer.append(str);
        }
        str = stringBuffer.toString() ;
        //获得的值是键值对

        //已知 String
        //需要转化成 Java 对象

        Gson gson = new Gson();
        //Gson有两个API
        //1.fromJson(string,T) 将字符串转化成java object
        //2.toJson(java Object) 将java object转化成json字符串，这样才能响应给客户端

        User user = gson.fromJson(str, User.class);

        System.out.println(user);
    }
}

@WebServlet("/axios03.do")
public class Axios03Servlet extends HttpServlet {
    @Override
    protected void service(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

        StringBuffer stringBuffer = new StringBuffer("");
        BufferedReader bufferedReader = request.getReader();
        String str = null ;
        while((str=bufferedReader.readLine())!=null){
            stringBuffer.append(str);
        }
        str = stringBuffer.toString() ;

        //已知 String
        //需要转化成 Java Object

        Gson gson = new Gson();
        //Gson有两个API
        //1.fromJson(string,T) 将字符串转化成java object
        //2.toJson(java Object) 将java object转化成json字符串，这样才能响应给客户端

        User user = gson.fromJson(str, User.class);
        user.setUname("鸠摩智");
        user.setPwd("123456");

        //假设user是从数据库查询出来的，现在需要将其转化成json格式的字符串，然后响应给客户端
        String userJsonStr = gson.toJson(user);
        response.setCharacterEncoding("UTF-8");
        //MIME-TYPE，告诉浏览器发送的格式
        response.setContentType("application/json;charset=utf-8");
        response.getWriter().write(userJsonStr);
    }
}