声明:删除springmvc的jar配置改成springboot的，若别的组件依赖springboot该升级就升级，该删掉就删掉，此文章只记录升级后的坑，升级springboot所需的jar请自行百度。

一.Hibernate的坑

概念:jpa和Hibernate的关系，jpa是接口，Hibernate是实现。

升级后yml文件配置数据库的代码

spring:
  datasource:
    driver-class-name: com.mysql.cj.jdbc.Driver
    url: jdbc:mysql://**:3306/**?autoReconnect=true
    username: ******
    password: ******

因为老代码没用Hibernate直接操作数据库,而是用Session操作的数据库，代码如下：

    @Autowired
    @Qualifier("sessionFactory")
    private SessionFactory sessionFactory;

    public Session getSession() {
        return this.sessionFactory.getCurrentSession();
    }

所以yml配置文件无法直接使用，需要重新配置数据源，若不配做则会报sessionFactory为null。
重新配置数据源如下代码：

import com.zaxxer.hikari.HikariDataSource;
import org.hibernate.SessionFactory;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.beans.factory.annotation.Qualifier;
import org.springframework.boot.autoconfigure.jdbc.DataSourceProperties;
import org.springframework.boot.autoconfigure.orm.jpa.HibernateProperties;
import org.springframework.boot.autoconfigure.orm.jpa.HibernateSettings;
import org.springframework.boot.autoconfigure.orm.jpa.JpaProperties;
import org.springframework.boot.context.properties.ConfigurationProperties;
import org.springframework.boot.orm.jpa.EntityManagerFactoryBuilder;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.Primary;
import org.springframework.data.jpa.repository.config.EnableJpaRepositories;
import org.springframework.orm.jpa.JpaTransactionManager;
import org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean;
import org.springframework.transaction.PlatformTransactionManager;
import org.springframework.transaction.annotation.EnableTransactionManagement;

import javax.persistence.EntityManagerFactory;
import javax.sql.DataSource;
import java.util.Map;


@Configuration
@EnableTransactionManagement
@EnableJpaRepositories
public class HibernateDataSourceConfig {

    @Autowired
    private JpaProperties jpaProperties;

    @Autowired
    private HibernateProperties hibernateProperties;

    @Bean(name = "dataSource")
    @ConfigurationProperties(prefix = "spring.datasource")
    public DataSource dataSource(DataSourceProperties properties) {
//        DataSource build =  DataSourceBuilder.create(properties.getClassLoader())
//                .type(HikariDataSource.class)
//                .driverClassName(properties.determineDriverClassName())
//                .url(properties.determineUrl())
//                .username(properties.determineUsername())
//                .password(properties.determinePassword())
//                .build();
//        return build;
        HikariDataSource dataSource = hikariDataSource();
        dataSource.setDriverClassName(properties.determineDriverClassName());
        dataSource.setJdbcUrl(properties.determineUrl());
        dataSource.setUsername(properties.determineUsername());
        dataSource.setPassword(properties.determinePassword());
        return dataSource;
    }

    private HikariDataSource hikariDataSource(){
        HikariDataSource dataSource = new HikariDataSource();
        dataSource.setMinimumIdle(0);
        dataSource.setMaximumPoolSize(10);
        dataSource.setAutoCommit(true);
        dataSource.setIdleTimeout(10000);
        dataSource.setPoolName("DatebookHikariCP");
        dataSource.setMaxLifetime(30000);
        dataSource.setConnectionTimeout(1000);
        dataSource.setConnectionTestQuery("SELECT 1");
        return dataSource;
    }

    @Bean(name = "entityManagerFactoryBean")
    @Primary
    public LocalContainerEntityManagerFactoryBean entityManagerFactoryBean(EntityManagerFactoryBuilder builder,@Qualifier("dataSource") DataSource dataSource){
        return builder.dataSource(dataSource)
                .properties(getVendorProperties(dataSource))
                //设置实体类所在位置
                .packages("***")
                .persistenceUnit("")
                .build();
    }


    private Map<String,Object> getVendorProperties(DataSource dataSource){
        // return jpaProperties.getHibernateProperties(dataSource);
        return hibernateProperties.determineHibernateProperties(jpaProperties.getProperties(), new HibernateSettings());
    }


    /**
     * EntityManagerFactory类似于Hibernate的SessionFactory,mybatis的SqlSessionFactory
     * 总之,在执行操作之前,我们总要获取一个EntityManager,这就类似于Hibernate的Session,
     * mybatis的sqlSession.
     * @param builder
     * @return
     */
    @Bean(name = "entityManagerFactory")
    public EntityManagerFactory entityManagerFactory(EntityManagerFactoryBuilder builder,@Qualifier("dataSource") DataSource dataSource){
        return this.entityManagerFactoryBean(builder,dataSource).getObject();
    }


    @Bean(name = "sessionFactory")
    public SessionFactory  sessionFactory(EntityManagerFactoryBuilder builder,@Qualifier("dataSource") DataSource dataSource){
        return this.entityManagerFactory(builder,dataSource).unwrap(SessionFactory.class);
    }

    /**
     * 配置事物管理器
     */
    @Bean(name = "transactionManager")
    public PlatformTransactionManager transactionManager(EntityManagerFactoryBuilder builder,@Qualifier("dataSource") DataSource dataSource){
        return new JpaTransactionManager(entityManagerFactory(builder,dataSource));
    }

}

数据源是用Hikari管理，但直接在yml配置Hikari参数不生效，所以Hikari参数写在代码中了。

二.GeneratedValue的坑

@Id
@GeneratedValue
@Column(
    name = "ID",
    updatable = false
)
private Long id;

以上的代码是老代码的配置,GeneratedValue中strategy默认配置是AUTO，所以直接执行保存会报错Table ‘xxx.hibernate_sequence’ doesn’t exist，因为升级spring-boot-starter-data-jpa使用了hibernate5，解决方法：以下两种

spring:
  jpa:
    hibernate:
      use-new-id-generator-mappings: false

@GeneratedValue(strategy = GenerationType.IDENTITY)

三.request.getParameterMap的坑

如上图，request.getParameterMap()在springmvc中可以获取到Content-Type: application/x-www-form-urlencoded中的值，但在springboot2中无法获取。若在springboot2中获取到值需要以下改造。

Enumeration<String> keys = request.getParameterNames();
 Map<String, String[]> resMap = new HashMap<>();
        while (keys.hasMoreElements()){
            String key = keys.nextElement();
            String[] value = request.getParameterValues(key);
            resMap.put(key,value);
        }

经历一天的改造，终于结束，但是不确定会不会有别的坑，需要多测试。