H2数据库设置本地文件库(Server Mode)时Spring

H2数据库配置为类似jdbc:h2:tcp://localhost/~/test/database的形式，就是Server Mode，如果没有单独启动H2服务器，那么会导致如下错误：

org.h2.jdbc.JdbcSQLException: Connection is broken: "java.net.ConnectException: Connection refused: connect: localhost" [90067-196]

Caused by: java.net.ConnectException: Connection refused: connect

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 org.h2.jdbc.JdbcSQLException: Connection is broken: "java.net.ConnectException: Connection refused: connect: localhost" [90067-196]

Caused by: org.springframework.jdbc.CannotGetJdbcConnectionException: Could not get JDBC Connection; nested exception is org.h2.jdbc.JdbcSQLException: Connection is broken: "java.net.ConnectException: Connection refused: connect: localhost" [90067-196]

org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'entityManagerFactory' defined in class path resource [org/springframework/boot/autoconfigure/orm/jpa/HibernateJpaAutoConfiguration.class]: Invocation of init method failed; nested exception is org.hibernate.service.spi.ServiceException: Unable to create requested service [org.hibernate.engine.jdbc.env.spi.JdbcEnvironment]

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

Caused by: org.hibernate.HibernateException: Access to DialectResolutionInfo cannot be null when 'hibernate.dialect' not set

大概就是连接失败一类的问题，网上说是因为springboot比h2服务器启动更早，然后导致这个错误的，具体原因还有待查证，解决方案是：

1. 创建类Starters（类名无所谓，后面引用就可以）

import org.h2.tools.Server;

public class Starters {

    private static final Logger logger = LoggerFactory.getLogger(Starters.class);

    public static void startH2Server() {
        try {
            Server h2Server = Server.createTcpServer().start(); // 关键代码
            if (h2Server.isRunning(true)) {
                logger.info("H2 server was started and is running.");
            } else {
                throw new RuntimeException("Could not start H2 server.");
            }
        } catch (SQLException e) {
            throw new RuntimeException("Failed to start H2 server: ", e);
        }
    }
}

注意：Springboot默认设置h2的依赖范围是runtime，需要删除那句代码才能编译时调用org.h2.tools.Server。

2. 分别在SpringBoot启动类ServletInitializer和Application中调用H2 server的启动代码

public class ServletInitializer extends SpringBootServletInitializer {

    @Override
    protected SpringApplicationBuilder configure(SpringApplicationBuilder application) {
        Starters.startH2Server(); // 关键代码
        return application.sources(Application.class);
    }
}

@SpringBootApplication
public class Application {

    public static void main(String[] args) {
        Starters.startH2Server(); // 关键代码
        SpringApplication.run(Application.class, args);
    }
}

这样修改之后，就可以正常启动了！

参考：How to start H2 TCP server on Spring Boot application startup?