java - centos7部署java-web项目时Tomcat无法连接mariadb

Question

当我在 IDEA 中启动 Web 项目时，一切都很好，包括与 mariadb 的连接。但是，当我将输出文件(war)放入/usr/share/tomcat/webapps/并使用命令“systemctl restart tomcat”重新启动 tomcat 服务时。打开firefox并输入网站“localhost:8080/online”。当我输入帐户和密码时，浏览器抛出无指针异常，这意味着我无法连接到 mariadb。 为什么以及如何处理这个问题？

环境:

$ uname -a
Linux bogon 3.10.0-957.el7.x86_64 #1 SMP Thu Nov 8 23:39:32 UTC 2018 x86_64 x86_64 x86_64 GNU/Linux
$ mysql --version
mysql  Ver 15.1 Distrib 5.5.60-MariaDB, for Linux (x86_64) using readline 5.1
$ tomcat version
Server version: Apache Tomcat/7.0.76
Server built:   Mar 12 2019 10:11:36 UTC
Server number:  7.0.76.0
OS Name:        Linux
OS Version:     3.10.0-957.el7.x86_64
Architecture:   amd64
JVM Version:    1.8.0_212-b04
JVM Vendor:     Oracle Corporation

Tomcat 状态:

$ systemctl status tomcat
● tomcat.service - Apache Tomcat Web Application Container
   Loaded: loaded (/usr/lib/systemd/system/tomcat.service; disabled; vendor preset: disabled)
   Active: active (running) since 二 2019-09-03 09:25:46 CST; 6s ago
 Main PID: 31464 (java)
    Tasks: 46
   CGroup: /system.slice/tomcat.service
           └─31464 /usr/lib/jvm/jre/bin/java -classpath /usr/share/tomcat/bin...

MariaDB 状态:

# systemctl status mariadb
● mariadb.service - MariaDB database server
   Loaded: loaded (/usr/lib/systemd/system/mariadb.service; disabled; vendor preset: disabled)
   Active: active (running) since 二 2019-09-03 07:15:24 CST; 2h 28min ago
  Process: 17937 ExecStartPost=/usr/libexec/mariadb-wait-ready $MAINPID (code=exited, status=0/SUCCESS)
  Process: 17905 ExecStartPre=/usr/libexec/mariadb-prepare-db-dir %n (code=exited, status=0/SUCCESS)
 Main PID: 17936 (mysqld_safe)
    Tasks: 20
   CGroup: /system.slice/mariadb.service
           ├─17936 /bin/sh /usr/bin/mysqld_safe --basedir=/usr
           └─18112 /usr/libexec/mysqld --basedir=/usr --datadir=/var/lib/mysq...

9月 03 07:15:20 bogon systemd[1]: Starting MariaDB database server...
9月 03 07:15:20 bogon mariadb-prepare-db-dir[17905]: Database MariaDB is pro...
9月 03 07:15:20 bogon mariadb-prepare-db-dir[17905]: If this is not the case...
9月 03 07:15:20 bogon mysqld_safe[17936]: 190903 07:15:20 mysqld_safe unkno...'
9月 03 07:15:20 bogon mysqld_safe[17936]: 190903 07:15:20 mysqld_safe Loggi....
9月 03 07:15:21 bogon mysqld_safe[17936]: 190903 07:15:21 mysqld_safe Start...l
9月 03 07:15:24 bogon systemd[1]: Started MariaDB database server.
Hint: Some lines were ellipsized, use -l to show in full.

网络应用程序:

# cd /usr/share/tomcat/webapps/
# ll
总用量 19880
drwxr-xr-x. 4 tomcat tomcat     4096 9月   3 07:35 online
-rw-r--r--. 1 root   root   20350442 9月   3 07:34 online.war

Tomcat日志信息:(/var/log/tomcat)

# cat localhost.2019-09-03.log
九月 03, 2019 7:17:51 上午 org.apache.catalina.core.ApplicationContext log
信息: No Spring WebApplicationInitializer types detected on classpath
九月 03, 2019 7:17:52 上午 org.apache.catalina.core.ApplicationContext log
信息: Initializing Spring FrameworkServlet 'spring'
九月 03, 2019 7:18:06 上午 org.apache.catalina.core.StandardWrapperValve invoke
严重: Servlet.service() for servlet [spring] in context with path [/online] threw exception [Request processing failed; nested exception is java.lang.NullPointerException] with root cause
java.lang.NullPointerException
    at bright.spring.dao.LoginDao.login(LoginDao.java:20)
    at bright.spring.controller.LoginController.login(LoginController.java:25)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:498)
    at org.springframework.web.method.support.InvocableHandlerMethod.doInvoke(InvocableHandlerMethod.java:221)
    at org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:136)
    at org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:114)
    at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:827)
    at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:738)
    at org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:85)
    at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:963)
    at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:897)
    at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:970)
    at org.springframework.web.servlet.FrameworkServlet.doPost(FrameworkServlet.java:872)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:650)
    at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:846)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:731)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:303)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
    at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:241)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:218)
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:110)
    at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:506)
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:169)
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:103)
    at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:962)
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:116)
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:445)
    at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1087)
    at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:637)
    at org.apache.tomcat.util.net.AprEndpoint$SocketProcessor.doRun(AprEndpoint.java:2549)
    at org.apache.tomcat.util.net.AprEndpoint$SocketProcessor.run(AprEndpoint.java:2538)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
    at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
    at java.lang.Thread.run(Thread.java:748)

LoginDao.java

package bright.spring.dao;

import java.sql.Connection;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import java.util.*;
import bright.spring.jdbc.JDBC;
import bright.spring.pojo.User;

public class LoginDao {
    /**/
    Map<String,String> u = new HashMap<>();
    /**/
    ResultSet rs = null;
    public Map<String,String> login(User user){
        try {
            Connection conn = JDBC.getConnection();
            Statement s = conn.createStatement();//LoginDao.java:20
            if(user.getIdentity().equals("student")){
                rs = s.executeQuery("select * from student where username ='"+user.getUsername()+"' and password ='"+user.getPassword()+"'");
                if(rs.next()){
                    u.put("name",rs.getString("studentName") );
                }else{
                    u.put("name","isnull" );
                }
            }else if(user.getIdentity().equals("teacher")){
                rs = s.executeQuery("select * from teacher where username ='"+user.getUsername()+"' and password ='"+user.getPassword()+"'");
                if(rs.next()){
                    u.put("name",rs.getString("teacherName") );
                }else{
                    u.put("name","isnull" );
                }
            }

        } catch (SQLException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        return u;
    }
}

类 JDBC:

package bright.spring.jdbc;

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;

public class JDBC {
static Connection conn;

    static{
        try {
            Class.forName("com.mysql.jdbc.Driver");
            System.out.println("");
        }catch (Exception e) {
            // TODO: handle exception
            e.printStackTrace();
        }
    }

    public static Connection getConnection() throws SQLException{
        try {
            /*conn = DriverManager.getConnection(
                    "jdbc:mysql://localhost:3306/onlineexp?useUnicode=true&characterEncoding=utf-8", "root", "ch96");*/
            conn = DriverManager.getConnection("jdbc:mysql://127.0.0.1:3306/onlineexp?useUnicode=true&characterEncoding=utf-8", "root", "ch96");
        } catch (SQLException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        return conn;
    }
}

Answer 1

我可以和你分享我的经验。我也面临同样类型的问题。在我的情况下，我使用 tomcat、Mysql、centOS。

经过长时间的研发我发现了三个问题。

• 其中之一是我使用 MySql 8 服务器。它有不同的驱动程序类“com.mysql.cj.jdbc.Driver”
• 第二个是 CentOS 防火墙不允许从主机 127.0.0.1 访问端口 3306/tcp 上的 MySQL 服务器
• 最后一个是Mysql 8默认的安全 future 。 (用户级别权限。)

您应该检查您案例中的所有此问题......