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老师为什么第一个打印出来不换行，加了第二个就换行

Python 全系列/第一阶段：Python入门/序列 14446楼

老师好像是我唤醒线程这一块出了问题运行连接都成功了就是聊天系统这一块似乎消息都在缓冲区我唤醒线程那一块出了问题但是我校对了几遍也没发现那里出错了

package com.bzsxt;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.net.ServerSocket;
import java.net.Socket;

/**
 * 接收客户端的线程类
 */
class ChatReceive extends Thread{
    private Socket socket;
    public ChatReceive(Socket socket) {
        this.socket = socket;
    }
    @Override
    public void run() {
        this.receiveMsg();
    }
    /**
     * 实现接收客户端发送的消息
     */
    private void receiveMsg(){
        BufferedReader br = null;
        try{
            br = new BufferedReader(new InputStreamReader(this.socket.getInputStream()));
            while(true){
                String msg = br.readLine();
                synchronized ("砸瓦鲁多"){
                    //把读取到的数据写入公共数据区
                    ChatRoomServer.buf="["+this.socket.getInetAddress()+"] "+msg;
                    //唤醒发送消息的线程对象
                    "砸瓦鲁多".notifyAll();
                }
            }
        }catch (Exception e){
            e.printStackTrace();
        }finally{
            if (br != null){
                try {
                    br.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
            if (this.socket != null){
                try {
                    this.socket.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
    }
}

/**
 * 向客户端发送消息的线程类
 */
class ChatSend extends Thread{
    private Socket socket;
    public ChatSend(Socket socket) {
        this.socket = socket;
    }
    @Override
    public void run() {
        this.sendMsg();
    }
    /**
     * 将公共数据区的消息发送给客户端
     */
    private void sendMsg(){
        PrintWriter pw = null;
        try{
            pw = new PrintWriter(this.socket.getOutputStream());
            while(true){
                synchronized ("砸瓦鲁多"){
                    //让发送消息的线程处于等待状态
                    "砸瓦鲁多".wait();
                    //将公共数据区中的消息发送给客户端
                    pw.print(ChatRoomServer.buf);
                    pw.flush();
                }
            }
        }catch (Exception e){
            e.printStackTrace();
        }finally {
            if (pw != null){
                pw.close();
            }
            if (this.socket != null){
                try {
                    this.socket.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
    }
}
public class ChatRoomServer {
    //定义公共数据区
    public static String buf;
    public static void main(String[] args) {
        System.out.println("Chat Server Version 1.0");
        System.out.println("Listen at 8888......");
        ServerSocket serverSocket = null;
        try{
            serverSocket = new ServerSocket(8888);
            while(true){
                Socket socket = serverSocket.accept();
                System.out.println("连接到："+socket.getInetAddress());
                new ChatReceive(socket).start();
                new ChatSend(socket).start();
            }
        }catch (Exception e){
            e.printStackTrace();
        }finally {
            if (serverSocket != null){
                try {
                    serverSocket.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
    }
}

JAVA 全系列/第二阶段：JAVA 基础深化和提高/网络编程（旧） 14447楼

为什么集合sets是不可变类型，我在网上搜都说是可变类型呀

人工智能/第二阶段：人工智能基础-Python基础/Python基础语法-旧 14448楼

老师，我的startup.bat可以正常启动，但是想在网页上看为什么会是这样的呢？

JAVA 全系列/第五阶段：JavaWeb开发/Servlet技术详解（旧） 14449楼

1625016444(1).jpg

我看了下评论区，也是这个问题，该怎么解决呢

JAVA 全系列/第一阶段：JAVA 快速入门/飞机大战小项目训练 14450楼

[WARNING] No mapping for GET /

7月 10, 2021 6:22:51 下午 org.apache.catalina.core.StandardWrapperValve invoke

严重: Servlet.service() for servlet [springmvc] in context with path [] threw exception [Request processing failed; nested exception is org.springframework.transaction.CannotCreateTransactionException: Could not open JDBC Connection for transaction; nested exception is com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: Communications link failure

The last packet sent successfully to the server was 0 milliseconds ago. The driver has not received any packets from the server.] with root cause

java.net.ConnectException: Connection refused: connect

at java.base/java.net.PlainSocketImpl.connect0(Native Method)

at java.base/java.net.PlainSocketImpl.socketConnect(PlainSocketImpl.java:101)

at java.base/java.net.AbstractPlainSocketImpl.doConnect(AbstractPlainSocketImpl.java:399)

at java.base/java.net.AbstractPlainSocketImpl.connectToAddress(AbstractPlainSocketImpl.java:242)

at java.base/java.net.AbstractPlainSocketImpl.connect(AbstractPlainSocketImpl.java:224)

at java.base/java.net.SocksSocketImpl.connect(SocksSocketImpl.java:403)

at java.base/java.net.Socket.connect(Socket.java:591)

at com.mysql.jdbc.StandardSocketFactory.connect(StandardSocketFactory.java:211)

at com.mysql.jdbc.MysqlIO.<init>(MysqlIO.java:298)

at com.mysql.jdbc.ConnectionImpl.coreConnect(ConnectionImpl.java:2253)

at com.mysql.jdbc.ConnectionImpl.connectOneTryOnly(ConnectionImpl.java:2286)

at com.mysql.jdbc.ConnectionImpl.createNewIO(ConnectionImpl.java:2085)

at com.mysql.jdbc.ConnectionImpl.<init>(ConnectionImpl.java:795)

at com.mysql.jdbc.JDBC4Connection.<init>(JDBC4Connection.java:44)

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:490)

at com.mysql.jdbc.Util.handleNewInstance(Util.java:404)

at com.mysql.jdbc.ConnectionImpl.getInstance(ConnectionImpl.java:400)

at com.mysql.jdbc.NonRegisteringDriver.connect(NonRegisteringDriver.java:327)

at java.sql/java.sql.DriverManager.getConnection(DriverManager.java:677)

at java.sql/java.sql.DriverManager.getConnection(DriverManager.java:189)

at org.springframework.jdbc.datasource.DriverManagerDataSource.getConnectionFromDriverManager(DriverManagerDataSource.java:155)

at org.springframework.jdbc.datasource.DriverManagerDataSource.getConnectionFromDriver(DriverManagerDataSource.java:146)

at org.springframework.jdbc.datasource.AbstractDriverBasedDataSource.getConnectionFromDriver(AbstractDriverBasedDataSource.java:205)

at org.springframework.jdbc.datasource.AbstractDriverBasedDataSource.getConnection(AbstractDriverBasedDataSource.java:169)

at org.springframework.jdbc.datasource.DataSourceTransactionManager.doBegin(DataSourceTransactionManager.java:263)

at org.springframework.transaction.support.AbstractPlatformTransactionManager.startTransaction(AbstractPlatformTransactionManager.java:400)

at org.springframework.transaction.support.AbstractPlatformTransactionManager.getTransaction(AbstractPlatformTransactionManager.java:373)

at org.springframework.transaction.interceptor.TransactionAspectSupport.createTransactionIfNecessary(TransactionAspectSupport.java:572)

at org.springframework.transaction.interceptor.TransactionAspectSupport.invokeWithinTransaction(TransactionAspectSupport.java:360)

at org.springframework.transaction.interceptor.TransactionInterceptor.invoke(TransactionInterceptor.java:99)

at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:186)

at org.springframework.aop.interceptor.ExposeInvocationInterceptor.invoke(ExposeInvocationInterceptor.java:95)

at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:186)

at org.springframework.aop.framework.JdkDynamicAopProxy.invoke(JdkDynamicAopProxy.java:212)

at com.sun.proxy.$Proxy40.addUsers(Unknown Source)

at com.bjsxt.web.controller.UsersController.addUsers(UsersController.java:22)

at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)

at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)

at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)

at java.base/java.lang.reflect.Method.invoke(Method.java:566)

at org.springframework.web.method.support.InvocableHandlerMethod.doInvoke(InvocableHandlerMethod.java:190)

at org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:138)

at org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:106)

at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:879)

at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:793)

at org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:87)

at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:1040)

at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:943)

at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:1006)

at org.springframework.web.servlet.FrameworkServlet.doPost(FrameworkServlet.java:909)

at javax.servlet.http.HttpServlet.service(HttpServlet.java:647)

at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:883)

at javax.servlet.http.HttpServlet.service(HttpServlet.java:728)

at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:305)

at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)

at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:51)

at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:243)

at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)

at org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:201)

at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:119)

at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:243)

at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)

at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:222)

at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:123)

at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:502)

at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:171)

at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:100)

at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:953)

at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:118)

at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:408)

at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1041)

at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:603)

at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:312)

at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1128)

at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:628)

at java.base/java.lang.Thread.run(Thread.java:834)

[WARNING] No mapping for GET /users/findUsers

7月 10, 2021 6:24:37 下午 org.apache.catalina.core.StandardWrapperValve invoke