Question

我开始引导一个新的Spring Boot project with JSP，我在控制台中收到以下错误，

java.sql.SQLException: Unable to load class: com.mysql.jdbc.Driver from ClassLoader:ParallelWebappClassLoader
  context: ROOT
  delegate: false
----------> Parent Classloader:
java.net.URLClassLoader@515f550a
;ClassLoader:ParallelWebappClassLoader
  context: ROOT
  delegate: false
----------> Parent Classloader:
java.net.URLClassLoader@515f550a


2017-09-25 10:23:51.958  WARN 1520 --- [on(2)-127.0.0.1] o.s.b.a.orm.jpa.DatabaseLookup           : Unable to determine jdbc url from datasource

org.springframework.jdbc.support.MetaDataAccessException: Could not get Connection for extracting meta data; nested exception is org.springframework.jdbc.CannotGetJdbcConnectionException: Could not get JDBC Connection; nested exception is java.sql.SQLException: Unable to load class: com.mysql.jdbc.Driver from ClassLoader:ParallelWebappClassLoader
  context: ROOT
  delegate: false
----------> Parent Classloader:
java.net.URLClassLoader@515f550a
;ClassLoader:ParallelWebappClassLoader
  context: ROOT
  delegate: false
----------> Parent Classloader:
java.net.URLClassLoader@515f550a

提供了项目结构，

当我添加新实体User并且代码在下面提供时，它就开始了

@Entity
@Table(name = "user")
public class User {

    private Long id;

    private String username;

    private String password;

    private String passwordConfirm;

//    private Set<Role> roles;

    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    public Long getId() {
        return id;
    }

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

    public String getUsername() {
        return username;
    }

    public void setUsername(String username) {
        this.username = username;
    }

    public String getPassword() {
        return password;
    }

    public void setPassword(String password) {
        this.password = password;
    }

    @Transient
    public String getPasswordConfirm() {
        return passwordConfirm;
    }

    public void setPasswordConfirm(String passwordConfirm) {
        this.passwordConfirm = passwordConfirm;
    }

//    @ManyToMany
//    @JoinTable(name = "user_role", joinColumns = @JoinColumn(name = "user_id"), inverseJoinColumns = @JoinColumn(name = "role_id"))
//    public Set<Role> getRoles() {
//        return roles;
//    }

//    public void setRoles(Set<Role> roles) {
//        this.roles = roles;
//    }
}

下面提供了WebApplication的代码，

@SpringBootApplication
public class WebApplication extends SpringBootServletInitializer {

    @Override
    protected SpringApplicationBuilder configure(SpringApplicationBuilder application) {
        return application.sources(WebApplication.class);
    }

    public static void main(String[] args) throws Exception {
        SpringApplication.run(WebApplication.class, args);
    }
}

最后，提供了pom.xml文件，

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <artifactId>hello-springboot</artifactId>
    <name>hello-springboot</name>
    <description>hello-springboot</description>
    <packaging>war</packaging>
    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>RELEASE</version>
    </parent>

    <properties>
        <java.version>1.8</java.version>
    </properties>

    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-data-jpa</artifactId>
        </dependency>

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-security</artifactId>
        </dependency>

        <dependency>
            <groupId>org.hsqldb</groupId>
            <artifactId>hsqldb</artifactId>
            <scope>runtime</scope>
        </dependency>

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-tomcat</artifactId>
            <scope>provided</scope>
        </dependency>

        <dependency>
            <groupId>org.apache.tomcat.embed</groupId>
            <artifactId>tomcat-embed-jasper</artifactId>
            <scope>provided</scope>
        </dependency>

        <dependency>
            <groupId>javax.servlet</groupId>
            <artifactId>jstl</artifactId>
        </dependency>

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-jdbc</artifactId>
        </dependency>
    </dependencies>


    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
            </plugin>
        </plugins>
    </build>
</project>

我计划在项目中使用HSQL数据库。下面提供的application.properties文件

server.port=8081
spring.mvc.view.prefix:/
spring.mvc.view.suffix:.jsp
spring.thymeleaf.cache=false
spring.application.name=Bootstrap Spring Boot
spring.thymeleaf.enabled=true 
spring.thymeleaf.prefix=classpath:/templates/
spring.thymeleaf.suffix=.html
spring.devtools.restart.additional-paths=.
#security.basic.enabled=true
#security.user.name=john
#security.user.password=123
#spring.datasource.driver-class-name=org.h2.Driver
#spring.datasource.url=jdbc:h2:mem:bootapp;DB_CLOSE_DELAY=-1;DB_CLOSE_ON_EXIT=FALSE
spring.datasource.username=testuser
spring.datasource.password=testpassword
server.error.path=/error
server.error.whitelabel.enabled=false 
# Set here configurations for the database connection
spring.datasource.url=jdbc:mysql://localhost:3306/Registration
# Username and secret
# Keep the connection alive if idle for a long time (needed in production)
spring.datasource.testWhileIdle=true
spring.datasource.validationQuery=SELECT 1
# ===============================
# = JPA / HIBERNATE
# ===============================
# Use spring.jpa.properties.* for Hibernate native properties (the prefix is
# stripped before adding them to the entity manager).
# Show or not log for each sql query
spring.jpa.show-sql=true
# Hibernate ddl auto (create, create-drop, update): with "update" the database
# schema will be automatically updated accordingly to java entities found in
# the project

spring.jpa.hibernate.ddl-auto=update
# Allows Hibernate to generate SQL optimized for a particular DBMS
spring.jpa.properties.hibernate.dialect=org.hibernate.dialect.MySQL5Dialect
#spring.mail.host=smtp.gmail.com
#spring.mail.username=ray.deng83@gmail.com
#spring.mail.password=Rochester25
#spring.mail.properties.mail.smtp.auth=true
#spring.mail.properties.mail.smtp.socketFactory.port=465
#spring.mail.properties.mail.smtp.socketFactory.class=javax.net.ssl.SSLSocketFactory
#spring.mail.properties.mail.smtp.socketFactory.fallback=false
#support.email=ray.deng83@gmail.com

这里有什么问题？

Answer 1

最近出现了这个看起来很奇怪的错误。我知道它已经过去了 3 年，但写这篇文章是为了社区。

如果您遇到此错误，请前往 catalina.out（如果您正在部署它）。通常错误 "ParallelWebappClassLoader" 不是您的问题，您应该查看此异常的末尾以找到 caused by xxxx 的内容，在那里您会看到其他一些详细错误的提及，我的情况是添加 json 依赖项您的可能正在添加您选择的 jdbc 依赖项（因为它是 Mysql）并将范围编译添加到它。

祝你好运。

无法加载类：来自ClassLoader的com.mysql.jdbc.Driver：ParallelWebappClassLoader

1 个答案: