本文将介绍trackerClient.getConnection()为null的详细情况，。我们将通过案例分析、数据研究等多种方式，帮助您更全面地了解这个主题，同时也将涉及一些关于.conn.Mana

本文将介绍trackerClient.getConnection()为null的详细情况，。我们将通过案例分析、数据研究等多种方式，帮助您更全面地了解这个主题，同时也将涉及一些关于.conn.ManagedClientConnectionImpl@604ed9f0 java.net.ConnectException: Connection refused: connect、.jdbc4.MySQLNonTransientConnectionException: No operations allowed after connection closed.、.MySQLNonTransientConnectionException: Could not create connection to database server. Attempted reconnect 5 times. Giving up.、c# – Asp.Net Core 2.0 ArgumentNullException：值不能为null.参数名称：connectionString的知识。

• trackerClient.getConnection()为null
• .conn.ManagedClientConnectionImpl@604ed9f0 java.net.ConnectException: Connection refused: connect
• .jdbc4.MySQLNonTransientConnectionException: No operations allowed after connection closed.
• .MySQLNonTransientConnectionException: Could not create connection to database server. Attempted reconnect 5 times. Giving up.
• c# – Asp.Net Core 2.0 ArgumentNullException：值不能为null.参数名称：connectionString

trackerClient.getConnection()为null

如题，整了个fastDFS文件服务器。但是集成项目spring boot时上传文件失败！

Debug到trackerClient.getConnection()时为null。于是看了服务器上tracker的log

[2019-04-25 12:10:23] INFO - file: tracker_relationship.c, line: 383, selecting leader...
[2019-04-25 12:10:23] ERROR - file: connection_pool.c, line: 110, connect to 124.179.281.198:22122 fail, errno: 113, error info: No route to host

主要做了两点修正：

一、原来的防火墙端口方通错了22122搞成了21222，改成了22122。同时检测安全组和防火墙其他端口，检测 /ect/fdfs下的其他.conf配置文件是否有误！

　　然后重启 tracker，satorage，Nginx

二、修改了fdfs_client.conf文件配置，这个不要在网上瞎copy别人的，一定要用官方的。同时确保这个文件能被读取到，读取文件路径一定要正确。

#################### FastDFS-Client Start ####################
#默认值为30s
connect_timeout = 10
#默认值为30s
network_timeout = 30
charset = UTF-8
http.tracker_http_port = 80
# token 防盗链功能
http.anti_steal_token = true
http.secret_key = FastDFS20091234567890
tracker_server = 192.168.1.118:22122
#tracker_server = 192.168.0.119:22122
## Tracker Server, if more than one, separate with ","
# fastdfs.tracker_servers=10.0.11.201:22122,10.0.11.202:22122,10.0.11.203:22122
#fastdfs.tracker_servers=${tracker_server_addr}:22122
#################### FastDFS-Client End ####################

好了，再重新上传就成功啦。

.conn.ManagedClientConnectionImpl@604ed9f0 java.net.ConnectException: Connection refused: connect

.jdbc4.MySQLNonTransientConnectionException: No operations allowed after connection closed.

com.mysql.jdbc.exceptions.jdbc4.MySQLNonTransientConnectionException: No operations allowed after connection closed.
    at sun.reflect.GeneratedConstructorAccessor65.newInstance(Unknown Source)
    at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
    at java.lang.reflect.Constructor.newInstance(Constructor.java:423)
    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:1015)
    at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:989)
    at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:975)
    at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:920)
    at com.mysql.jdbc.ConnectionImpl.throwConnectionClosedException(ConnectionImpl.java:1311)
    at com.mysql.jdbc.ConnectionImpl.checkClosed(ConnectionImpl.java:1303)
    at com.mysql.jdbc.ConnectionImpl.createStatement(ConnectionImpl.java:2683)
    at com.mysql.jdbc.ConnectionImpl.createStatement(ConnectionImpl.java:2665)
    at security.view.util.SqlUtils.insert(SqlUtils.java:315)
    at security.view.util.SqlUtils.processKill(SqlUtils.java:109)
    at security.view.util.SqlUtils.sql(SqlUtils.java:148)
    at security.view.util.SqlUtils.sqlJsonObj(SqlUtils.java:418)
    at security.view.util.SqlUtils.processKill(SqlUtils.java:97)
    at security.view.util.SqlUtils.sql(SqlUtils.java:148)
 

.MySQLNonTransientConnectionException: Could not create connection to database server. Attempted reconnect 5 times. Giving up.

com.mysql.jdbc.exceptions.jdbc4.MySQLNonTransientConnectionException: Could not create connection to database server. Attempted reconnect 5 times. Giving up.
	at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
	at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:62)
	at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
	at java.lang.reflect.Constructor.newInstance(Constructor.java:408)
	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:1015)
	at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:989)
	at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:975)
	at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:920)
	at com.mysql.jdbc.ConnectionImpl.connectWithRetries(ConnectionImpl.java:2385)
	at com.mysql.jdbc.ConnectionImpl.createNewIO(ConnectionImpl.java:2306)
	at com.mysql.jdbc.ConnectionImpl.<init>(ConnectionImpl.java:834)
	at com.mysql.jdbc.JDBC4Connection.<init>(JDBC4Connection.java:47)
	at sun.reflect.GeneratedConstructorAccessor4.newInstance(Unknown Source)
	at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
	at java.lang.reflect.Constructor.newInstance(Constructor.java:408)
	at com.mysql.jdbc.Util.handleNewInstance(Util.java:411)
	at com.mysql.jdbc.ConnectionImpl.getInstance(ConnectionImpl.java:416)
	at com.mysql.jdbc.NonRegisteringDriver.connect(NonRegisteringDriver.java:346)
	at com.mysql.jdbc.jdbc2.optional.MysqlDataSource.getConnection(MysqlDataSource.java:443)
	at com.mysql.jdbc.jdbc2.optional.MysqlDataSource.getConnection(MysqlDataSource.java:141)
	at com.mysql.jdbc.jdbc2.optional.MysqlDataSource.getConnection(MysqlDataSource.java:111)
	at cn.qjj.mysql.MySQLPool.getNewConnection(MySQLPool.java:72)
	at cn.qjj.mysql.MySQLPool.init(MySQLPool.java:63)
	at cn.qjj.mysql.MySQLPool.<init>(MySQLPool.java:32)
	at cn.qjj.mysql.MySQLPool.getInstance(MySQLPool.java:39)
	at cn.qjj.mysql.SqlUtils.<clinit>(SqlUtils.java:33)
	at cn.qjj.solr.MsgUtil.main(MsgUtil.java:31)
Caused by: com.mysql.jdbc.exceptions.jdbc4.MySQLNonTransientConnectionException: Data source rejected establishment of connection,  message from server: "Too many connections"
	at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
	at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:62)
	at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
	at java.lang.reflect.Constructor.newInstance(Constructor.java:408)
	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:1015)
	at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:989)
	at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:975)
	at com.mysql.jdbc.MysqlIO.doHandshake(MysqlIO.java:1112)
	at com.mysql.jdbc.ConnectionImpl.coreConnect(ConnectionImpl.java:2483)
	at com.mysql.jdbc.ConnectionImpl.connectWithRetries(ConnectionImpl.java:2324)
	... 18 more
java.lang.NullPointerException
	at java.util.concurrent.ConcurrentHashMap.putVal(ConcurrentHashMap.java:1011)
	at java.util.concurrent.ConcurrentHashMap.put(ConcurrentHashMap.java:1006)
	at cn.qjj.mysql.MySQLPool.init(MySQLPool.java:63)
	at cn.qjj.mysql.MySQLPool.<init>(MySQLPool.java:32)
	at cn.qjj.mysql.MySQLPool.getInstance(MySQLPool.java:39)
	at cn.qjj.mysql.SqlUtils.<clinit>(SqlUtils.java:33)
	at cn.qjj.solr.MsgUtil.main(MsgUtil.java:31)

c# – Asp.Net Core 2.0 ArgumentNullException：值不能为null.参数名称：connectionString

public class Startup
{
    public Startup(IConfiguration configuration)
    {
        Configuration = configuration;
    }

    public IConfiguration Configuration { get; }

    public void ConfigureServices(IServiceCollection services)
    {    
        services.AddMvc();
        services.AddDbContext<VideosContext>(options => options.UsesqlServer(Configuration.GetConnectionString("DefaultConnection")));
    }

    public void Configure(IApplicationBuilder app,IHostingEnvironment env)
    {
        if (env.IsDevelopment())
        {
            app.UsebrowserLink();
            app.UseDeveloperExceptionPage();
        }
        else
        {
            app.UseExceptionHandler("/Home/Error");
        }

        app.UseStaticFiles();

        app.UseMvc(routes =>
        {
            routes.MapRoute(
name: "default",template: "{controller=Home}/{action=Index}/{id?}");
        });
    }
}
    {
      "ConnectionString": {
        "DefaultConnection": "Server =(localdb)\\mssqllocaldb;Database=Videos;Trusted_Connection=True;MultipleActiveResultSets=true"
    },"Logging": {
      "IncludeScopes": false,"LogLevel": {
        "Default": "Warning"
      }
    }
}

public static void Main(string[] args)
{
     BuildWebHost(args).Run();
}

public static IWebHost BuildWebHost(string[] args) =>
   WebHost.CreateDefaultBuilder(args)
      .UseStartup<Startup>()
      .Build();

{
    "ConnectionStrings": {
        "DefaultConnection": "Server =(localdb)\\mssqllocaldb;Database=Videos;Trusted_Connection=True;MultipleActiveResultSets=true"
    }
}

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