发生500错误，数据库连接失败，我用的是mysql8.0

com.mysql.jdbc.exceptions.jdbc4.MySQLNonTransientConnectionException: Client does not support authentication protocol requested by server; consider upgrading MySQL client
	at java.base/jdk.internal.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
	at java.base/jdk.internal.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:62)
	at java.base/jdk.internal.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
	at java.base/java.lang.reflect.Constructor.newInstance(Constructor.java:488)
	at com.mysql.jdbc.Util.handleNewInstance(Util.java:411)
	at com.mysql.jdbc.Util.getInstance(Util.java:386)
	at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:1013)
	at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:3609)
	at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:3541)
	at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:943)
	at com.mysql.jdbc.MysqlIO.secureAuth411(MysqlIO.java:4113)
创建数据库连接失败。
at com.mysql.jdbc.MysqlIO.doHandshake(MysqlIO.java:1308)
	at com.mysql.jdbc.ConnectionImpl.coreConnect(ConnectionImpl.java:2336)
	at com.mysql.jdbc.ConnectionImpl.connectOneTryOnly(ConnectionImpl.java:2369)
	at com.mysql.jdbc.ConnectionImpl.createNewIO(ConnectionImpl.java:2153)
	at com.mysql.jdbc.ConnectionImpl.<init>(ConnectionImpl.java:792)
	at com.mysql.jdbc.JDBC4Connection.<init>(JDBC4Connection.java:47)
	at java.base/jdk.internal.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
	at java.base/jdk.internal.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:62)
	at java.base/jdk.internal.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
	at java.base/java.lang.reflect.Constructor.newInstance(Constructor.java:488)
	at com.mysql.jdbc.Util.handleNewInstance(Util.java:411)
	at com.mysql.jdbc.ConnectionImpl.getInstance(ConnectionImpl.java:381)
	at com.mysql.jdbc.NonRegisteringDriver.connect(NonRegisteringDriver.java:305)
	at java.sql/java.sql.DriverManager.getConnection(DriverManager.java:677)
	at java.sql/java.sql.DriverManager.getConnection(DriverManager.java:228)
	at com.imooc.jdbc.common.ConnectionUtil.getConnection(ConnectionUtil.java:39)
	at com.imooc.jdbc.dao.MessageDAO.getMessages(MessageDAO.java:55)
	at com.imooc.jdbc.service.MessageService.getMessages(MessageService.java:34)
	at com.imooc.jdbc.servlet.MessageListServlet.service(MessageListServlet.java:41)
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:741)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:231)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
	at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:53)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
	at com.imooc.jdbc.filter.UserFilter.doFilter(UserFilter.java:30)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
	at com.imooc.jdbc.filter.CharsetEncodingFilter.doFilter(CharsetEncodingFilter.java:28)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
	at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:199)
	at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:96)
	at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:490)
	at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:139)
	at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:92)
	at org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:668)
	at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:74)
	at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:343)
	at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:408)
	at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:66)

package com.imooc.jdbc.common;

import com.mchange.v2.c3p0.ComboPooledDataSource;

import java.sql.*;

/**
 * 数据库操作公共类
 *
 * @version 1.0
 */
public final class ConnectionUtil {

    private static final ComboPooledDataSource DATA_SOURCE = new ComboPooledDataSource();

    /**
     * 获得数据库连接
     * @return
     */
    public static Connection getConnection() {
        Connection conn = null;
        try {
            conn = DATA_SOURCE.getConnection();
        } catch (SQLException e) {
            System.out.println("连接数据库失败");
            e.printStackTrace();
        }
        return conn;
    }

    /**
     * 释放数据库资源
     * @param rs ResultSet
     * @param stmt Statement
     * @param conn Connection
     */
    public static void release(ResultSet rs, Statement stmt, Connection conn) {
        try {
            if (rs != null) {
                rs.close();
            }
        } catch (SQLException e) {
            e.printStackTrace();
        } finally {
            try {
                if (stmt != null) {
                    stmt.close();
                }
            } catch (SQLException e) {
                e.printStackTrace();
            } finally {
                try {
                    if (conn != null) {
                        conn.close();
                    }
                } catch (SQLException e) {
                    e.printStackTrace();
                }
            }
        }
    }

}

<?xml version="1.0" encoding="UTF-8"?>
<c3p0-config>

  <default-config>
    <property name="driverClass">com.mysql.cj.jdbc.Driver</property>
   <property name="jdbcUrl">jdbc:mysql://localhost:3306/cdb3?characterEncoding=utf-8&amp;useSSL=false&amp;serverTimezone=Hongkong&amp;rewriteBatchedStatements=true</property>
   <property name="user">root</property>
   <property name="password">123456</property>
   <property name="initialPoolSize">5</property>
   <property name="maxPoolSize">20</property>
  </default-config>
  
</c3p0-config>