java - 连接数据库的连接过多

Question

我是 Hibernate 初学者。我只是尝试连接到数据库，但失败并收到这些错误:

Type Exception Report

Message: Unable to create requested service [org.hibernate.engine.jdbc.env.spi.JdbcEnvironment]

Description The server encountered an unexpected condition that prevented it from fulfilling the request.

Exception

org.hibernate.service.spi.ServiceException: Unable to create requested service [org.hibernate.engine.jdbc.env.spi.JdbcEnvironment]
    org.hibernate.service.internal.AbstractServiceRegistryImpl.createService(AbstractServiceRegistryImpl.java:275)
    org.hibernate.service.internal.AbstractServiceRegistryImpl.initializeService(AbstractServiceRegistryImpl.java:237)
    org.hibernate.service.internal.AbstractServiceRegistryImpl.getService(AbstractServiceRegistryImpl.java:214)
    org.hibernate.id.factory.internal.DefaultIdentifierGeneratorFactory.injectServices(DefaultIdentifierGeneratorFactory.java:152)
    org.hibernate.service.internal.AbstractServiceRegistryImpl.injectDependencies(AbstractServiceRegistryImpl.java:286)
    org.hibernate.service.internal.AbstractServiceRegistryImpl.initializeService(AbstractServiceRegistryImpl.java:243)
    org.hibernate.service.internal.AbstractServiceRegistryImpl.getService(AbstractServiceRegistryImpl.java:214)
    org.hibernate.boot.internal.InFlightMetadataCollectorImpl.<init>(InFlightMetadataCollectorImpl.java:175)
    org.hibernate.boot.model.process.spi.MetadataBuildingProcess.complete(MetadataBuildingProcess.java:118)
    org.hibernate.boot.model.process.spi.MetadataBuildingProcess.build(MetadataBuildingProcess.java:83)
    org.hibernate.boot.internal.MetadataBuilderImpl.build(MetadataBuilderImpl.java:473)
    org.hibernate.boot.internal.MetadataBuilderImpl.build(MetadataBuilderImpl.java:84)
    org.hibernate.cfg.Configuration.buildSessionFactory(Configuration.java:689)
    model.CategoryHelper.<init>(CategoryHelper.java:28)
    serv.MyFirst.doGet(MyFirst.java:21)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:635)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:742)
    org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
Root Cause

org.hibernate.exception.JDBCConnectionException: Error calling Driver#connect
    org.hibernate.exception.internal.SQLExceptionTypeDelegate.convert(SQLExceptionTypeDelegate.java:48)
    org.hibernate.exception.internal.StandardSQLExceptionConverter.convert(StandardSQLExceptionConverter.java:42)
    org.hibernate.engine.jdbc.spi.SqlExceptionHelper.convert(SqlExceptionHelper.java:113)
    org.hibernate.engine.jdbc.connections.internal.BasicConnectionCreator.convertSqlException(BasicConnectionCreator.java:118)
    org.hibernate.engine.jdbc.connections.internal.DriverConnectionCreator.makeConnection(DriverConnectionCreator.java:41)
    org.hibernate.engine.jdbc.connections.internal.BasicConnectionCreator.createConnection(BasicConnectionCreator.java:58)
    org.hibernate.engine.jdbc.connections.internal.DriverManagerConnectionProviderImpl$PooledConnections.addConnections(DriverManagerConnectionProviderImpl.java:321)
    org.hibernate.engine.jdbc.connections.internal.DriverManagerConnectionProviderImpl$PooledConnections.<init>(DriverManagerConnectionProviderImpl.java:240)
    org.hibernate.engine.jdbc.connections.internal.DriverManagerConnectionProviderImpl$PooledConnections.<init>(DriverManagerConnectionProviderImpl.java:218)
    org.hibernate.engine.jdbc.connections.internal.DriverManagerConnectionProviderImpl$PooledConnections$Builder.build(DriverManagerConnectionProviderImpl.java:359)
    org.hibernate.engine.jdbc.connections.internal.DriverManagerConnectionProviderImpl.buildPool(DriverManagerConnectionProviderImpl.java:98)
    org.hibernate.engine.jdbc.connections.internal.DriverManagerConnectionProviderImpl.configure(DriverManagerConnectionProviderImpl.java:73)
    org.hibernate.boot.registry.internal.StandardServiceRegistryImpl.configureService(StandardServiceRegistryImpl.java:107)
    org.hibernate.service.internal.AbstractServiceRegistryImpl.initializeService(AbstractServiceRegistryImpl.java:246)
    org.hibernate.service.internal.AbstractServiceRegistryImpl.getService(AbstractServiceRegistryImpl.java:214)
    org.hibernate.engine.jdbc.env.internal.JdbcEnvironmentInitiator.buildJdbcConnectionAccess(JdbcEnvironmentInitiator.java:145)
    org.hibernate.engine.jdbc.env.internal.JdbcEnvironmentInitiator.initiateService(JdbcEnvironmentInitiator.java:66)
    org.hibernate.engine.jdbc.env.internal.JdbcEnvironmentInitiator.initiateService(JdbcEnvironmentInitiator.java:35)
    org.hibernate.boot.registry.internal.StandardServiceRegistryImpl.initiateService(StandardServiceRegistryImpl.java:101)
    org.hibernate.service.internal.AbstractServiceRegistryImpl.createService(AbstractServiceRegistryImpl.java:263)
    org.hibernate.service.internal.AbstractServiceRegistryImpl.initializeService(AbstractServiceRegistryImpl.java:237)
    org.hibernate.service.internal.AbstractServiceRegistryImpl.getService(AbstractServiceRegistryImpl.java:214)
    org.hibernate.id.factory.internal.DefaultIdentifierGeneratorFactory.injectServices(DefaultIdentifierGeneratorFactory.java:152)
    org.hibernate.service.internal.AbstractServiceRegistryImpl.injectDependencies(AbstractServiceRegistryImpl.java:286)
    org.hibernate.service.internal.AbstractServiceRegistryImpl.initializeService(AbstractServiceRegistryImpl.java:243)
    org.hibernate.service.internal.AbstractServiceRegistryImpl.getService(AbstractServiceRegistryImpl.java:214)
    org.hibernate.boot.internal.InFlightMetadataCollectorImpl.<init>(InFlightMetadataCollectorImpl.java:175)
    org.hibernate.boot.model.process.spi.MetadataBuildingProcess.complete(MetadataBuildingProcess.java:118)
    org.hibernate.boot.model.process.spi.MetadataBuildingProcess.build(MetadataBuildingProcess.java:83)
    org.hibernate.boot.internal.MetadataBuilderImpl.build(MetadataBuilderImpl.java:473)
    org.hibernate.boot.internal.MetadataBuilderImpl.build(MetadataBuilderImpl.java:84)
    org.hibernate.cfg.Configuration.buildSessionFactory(Configuration.java:689)
    model.CategoryHelper.<init>(CategoryHelper.java:28)
    serv.MyFirst.doGet(MyFirst.java:21)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:635)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:742)
    org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
Root Cause

java.sql.SQLNonTransientConnectionException: Data source rejected establishment of connection,  message from server: "Too many connections"
    com.mysql.cj.jdbc.exceptions.SQLError.createSQLException(SQLError.java:110)
    com.mysql.cj.jdbc.exceptions.SQLError.createSQLException(SQLError.java:97)
    com.mysql.cj.jdbc.exceptions.SQLExceptionsMapping.translateException(SQLExceptionsMapping.java:122)
    com.mysql.cj.jdbc.ConnectionImpl.createNewIO(ConnectionImpl.java:835)
    com.mysql.cj.jdbc.ConnectionImpl.<init>(ConnectionImpl.java:455)
    com.mysql.cj.jdbc.ConnectionImpl.getInstance(ConnectionImpl.java:240)
    com.mysql.cj.jdbc.NonRegisteringDriver.connect(NonRegisteringDriver.java:199)
    org.hibernate.engine.jdbc.connections.internal.DriverConnectionCreator.makeConnection(DriverConnectionCreator.java:38)
    org.hibernate.engine.jdbc.connections.internal.BasicConnectionCreator.createConnection(BasicConnectionCreator.java:58)
    org.hibernate.engine.jdbc.connections.internal.DriverManagerConnectionProviderImpl$PooledConnections.addConnections(DriverManagerConnectionProviderImpl.java:321)
    org.hibernate.engine.jdbc.connections.internal.DriverManagerConnectionProviderImpl$PooledConnections.<init>(DriverManagerConnectionProviderImpl.java:240)
    org.hibernate.engine.jdbc.connections.internal.DriverManagerConnectionProviderImpl$PooledConnections.<init>(DriverManagerConnectionProviderImpl.java:218)
    org.hibernate.engine.jdbc.connections.internal.DriverManagerConnectionProviderImpl$PooledConnections$Builder.build(DriverManagerConnectionProviderImpl.java:359)
    org.hibernate.engine.jdbc.connections.internal.DriverManagerConnectionProviderImpl.buildPool(DriverManagerConnectionProviderImpl.java:98)
    org.hibernate.engine.jdbc.connections.internal.DriverManagerConnectionProviderImpl.configure(DriverManagerConnectionProviderImpl.java:73)
    org.hibernate.boot.registry.internal.StandardServiceRegistryImpl.configureService(StandardServiceRegistryImpl.java:107)
    org.hibernate.service.internal.AbstractServiceRegistryImpl.initializeService(AbstractServiceRegistryImpl.java:246)
    org.hibernate.service.internal.AbstractServiceRegistryImpl.getService(AbstractServiceRegistryImpl.java:214)
    org.hibernate.engine.jdbc.env.internal.JdbcEnvironmentInitiator.buildJdbcConnectionAccess(JdbcEnvironmentInitiator.java:145)
    org.hibernate.engine.jdbc.env.internal.JdbcEnvironmentInitiator.initiateService(JdbcEnvironmentInitiator.java:66)
    org.hibernate.engine.jdbc.env.internal.JdbcEnvironmentInitiator.initiateService(JdbcEnvironmentInitiator.java:35)
    org.hibernate.boot.registry.internal.StandardServiceRegistryImpl.initiateService(StandardServiceRegistryImpl.java:101)
    org.hibernate.service.internal.AbstractServiceRegistryImpl.createService(AbstractServiceRegistryImpl.java:263)
    org.hibernate.service.internal.AbstractServiceRegistryImpl.initializeService(AbstractServiceRegistryImpl.java:237)
    org.hibernate.service.internal.AbstractServiceRegistryImpl.getService(AbstractServiceRegistryImpl.java:214)
    org.hibernate.id.factory.internal.DefaultIdentifierGeneratorFactory.injectServices(DefaultIdentifierGeneratorFactory.java:152)
    org.hibernate.service.internal.AbstractServiceRegistryImpl.injectDependencies(AbstractServiceRegistryImpl.java:286)
    org.hibernate.service.internal.AbstractServiceRegistryImpl.initializeService(AbstractServiceRegistryImpl.java:243)
    org.hibernate.service.internal.AbstractServiceRegistryImpl.getService(AbstractServiceRegistryImpl.java:214)
    org.hibernate.boot.internal.InFlightMetadataCollectorImpl.<init>(InFlightMetadataCollectorImpl.java:175)
    org.hibernate.boot.model.process.spi.MetadataBuildingProcess.complete(MetadataBuildingProcess.java:118)
    org.hibernate.boot.model.process.spi.MetadataBuildingProcess.build(MetadataBuildingProcess.java:83)
    org.hibernate.boot.internal.MetadataBuilderImpl.build(MetadataBuilderImpl.java:473)
    org.hibernate.boot.internal.MetadataBuilderImpl.build(MetadataBuilderImpl.java:84)
    org.hibernate.cfg.Configuration.buildSessionFactory(Configuration.java:689)
    model.CategoryHelper.<init>(CategoryHelper.java:28)
    serv.MyFirst.doGet(MyFirst.java:21)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:635)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:742)
    org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
Note The full stack trace of the root cause is available in the server logs.

类别类

package model;

import java.util.Objects;

public class CategoryClass {
    private int id;
    private String name;

    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (o == null || getClass() != o.getClass()) return false;
        CategoryClass that = (CategoryClass) o;
        return id == that.id &&
                Objects.equals(name, that.name);
    }

    @Override
    public int hashCode() {
        return Objects.hash(id, name);
    }
}

类别助手

package model;

import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.boot.registry.StandardServiceRegistryBuilder;
import org.hibernate.cfg.Configuration;
import org.hibernate.query.Query;
import org.hibernate.service.ServiceRegistry;
import java.util.List;

public class CategoryHelper {
    private SessionFactory MySessionFactory;

    public CategoryHelper() {
        Configuration configuration = new Configuration().configure("hibernate.cfg.xml");
        StandardServiceRegistryBuilder serviceRegistryBuilder = new StandardServiceRegistryBuilder();
        serviceRegistryBuilder.applySettings(configuration.getProperties());
        ServiceRegistry serviceRegistry = serviceRegistryBuilder.build();
        MySessionFactory = configuration.buildSessionFactory(serviceRegistry);
    }

    public List<model.CategoryClass> getCategories() {
        Session session = MySessionFactory.openSession();
        Query query = session.createQuery("from model.CategoryClass");
        List<model.CategoryClass> categoryClasses = query.list();
        session.close();
        return categoryClasses;
    }
}

CategoryClass.hbm.xml

<?xml version='1.0' encoding='utf-8'?>
<!DOCTYPE hibernate-mapping PUBLIC
    "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
    "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">
<hibernate-mapping>
    <class name="model.CategoryClass" table="category" schema="shopping">
        <id name="id">
            <column name="id" sql-type="int(11)"/>
        </id>
        <property name="name">
            <column name="name" sql-type="varchar(45)" length="45"/>
        </property>
    </class>
</hibernate-mapping>

hibernate.cfg.xml

<hibernate-configuration>
    <session-factory>
        <property name="hibernate.dialect">org.hibernate.dialect.MySQL5Dialect</property>
        <property name="connection.url">jdbc:mysql://localhost:3306/shopping</property>
        <property name="connection.driver_class">com.mysql.jdbc.Driver</property>
        <property name="connection.username">root</property>
        <property name="connection.password">avadakedavra13</property>
        <mapping resource="model/CategoryClass.hbm.xml"/>
        <mapping class="model.CategoryClass"/>
    </session-factory>
</hibernate-configuration>

MyFirst.java(Servlet)

package serv;

import model.CategoryClass;
import model.CategoryHelper;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.util.List;

public class MyFirst extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        CategoryHelper categoryHelper = new CategoryHelper();
        List<CategoryClass> Categorieslist = categoryHelper.getCategories();
        request.setAttribute("categories", Categorieslist);
        request.getRequestDispatcher("/header.jsp").forward(request, response);
    }
}

这是我的项目的目录结构:

错误的一些行引起了我的注意，如下所示:

com.mysql.cj.jdbc.NonRegisteringDriver.connect(NonRegisteringDriver.java:199)

我正在使用 mysql-connector-java 8.0.15，打开 3306 端口并运行 mysqld，但仍然出现这些错误。

<小时/>

更新

类别助手

package model;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.boot.registry.StandardServiceRegistryBuilder;
import org.hibernate.cfg.Configuration;
import org.hibernate.query.Query;
import org.hibernate.service.ServiceRegistry;

import java.util.List;

public class CategoryHelper {


    private SessionFactory MySessionFactory;

    public CategoryHelper() {

        Configuration configuration = new Configuration().configure("hibernate.cfg.xml");

        StandardServiceRegistryBuilder serviceRegistryBuilder = new StandardServiceRegistryBuilder();

        serviceRegistryBuilder.applySettings(configuration.getProperties());

        ServiceRegistry serviceRegistry = serviceRegistryBuilder.build();

        MySessionFactory = configuration.buildSessionFactory(serviceRegistry);

   }

    public List<model.CategoryClass> getCategories() {


        try (Session session = MySessionFactory.openSession()) {
            Query query = session.createQuery("from model.CategoryClass");
            List<model.CategoryClass> categoryClasses = query.list();
            return categoryClasses;
        }
    }


}

MyFirst.java(Servlet)

package serv;

import model.CategoryClass;
import model.CategoryHelper;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.util.List;

public class MyFirst extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws  IOException {

    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws IOException {


        CategoryHelper categoryHelper = new CategoryHelper();
        List<CategoryClass> Categorieslist = categoryHelper.getCategories();
        request.setAttribute("categories", Categorieslist);

        try {
            request.getRequestDispatcher("/header.jsp").forward(request, response);
        } catch (ServletException e) {
            e.printStackTrace();
        }


    }
}

Answer 1

您已将 throws ServletException 添加到所有方法的签名中，而不是在出错时关闭连接。连接已打开，因此出现错误。我建议改用 try-with-resources。