nacos只支持mysql的原因分析

什么是Nacos

英文全称Dynamic Naming and Configuration Service，Na为naming/nameServer即注册中心,co为configuration即注册中心，service是指该注册/配置中心都是以服务为核心。服务在nacos是一等公民

没看源码之前,觉得很离谱,为啥只能限制数据库为mysql,按道理来说,nacos用了JdbcTemplate,可以适配很多数据库才是

最近看了nacos的源码,发现其中有很多硬编码,才明白原因

nacos的数据源获取都是通过com.alibaba.nacos.config.server.service.datasource.DynamicDataSource来获取的

在获取数据源时,根据配置判断你到底是使用内置的本地数据库还是外部的数据库(mysql)

public synchronized DataSourceService getDataSource() {
   try {

// Embedded storage is used by default in stand-alone mode
       // In cluster mode, external databases are used by default
       // 根据System.getProperty("nacos.standalone")来判断你到底是不是standalone模式
       // standalone模式,使用内置数据库
       if (PropertyUtil.isEmbeddedStorage()) {
           if (localDataSourceService == null) {
               localDataSourceService = new LocalDataSourceServiceImpl();
               localDataSourceService.init();
           }
           return localDataSourceService;
       } else {
           // 如果不是standalone,直接创建外部的数据源
           if (basicDataSourceService == null) {
               basicDataSourceService = new ExternalDataSourceServiceImpl();
               basicDataSourceService.init();
           }
           return basicDataSourceService;
       }
   } catch (Exception e) {
       throw new RuntimeException(e);
   }
}

外部数据源com.alibaba.nacos.config.server.service.datasource.ExternalDataSourceServiceImpl.init()

@Override
public void init() {
   queryTimeout = ConvertUtils.toInt(System.getProperty("QUERYTIMEOUT"), 3);
   jt = new JdbcTemplate();
   // Set the maximum number of records to prevent memory expansion
   jt.setMaxRows(50000);
   jt.setQueryTimeout(queryTimeout);
   testMasterJT = new JdbcTemplate();
   testMasterJT.setQueryTimeout(queryTimeout);
   testMasterWritableJT = new JdbcTemplate();
   // Prevent the login interface from being too long because the main library is not available
   testMasterWritableJT.setQueryTimeout(1);
   //  Database health check
   testJtList = new ArrayList<JdbcTemplate>();
   isHealthList = new ArrayList<Boolean>();
   tm = new DataSourceTransactionManager();
   tjt = new TransactionTemplate(tm);
   // Transaction timeout needs to be distinguished from ordinary operations.
   tjt.setTimeout(TRANSACTION_QUERY_TIMEOUT);
   // 判断到底是是不是用外部数据库
   // 这个可以在com.alibaba.nacos.config.server.utils.PropertyUtil#loadSetting中看到
   // setUseExternalDB("mysql".equalsIgnoreCase(getString("spring.datasource.platform", "")));
   // 好家伙,直接判断配置的是不是mysql,是mysql那就是外部数据库,进行reload,不是,那就不管了
   if (PropertyUtil.isUseExternalDB()) {
       try {
           reload();
       } catch (IOException e) {
           e.printStackTrace();
           throw new RuntimeException(DB_LOAD_ERROR_MSG);
       }
       if (this.dataSourceList.size() > DB_MASTER_SELECT_THRESHOLD) {
           ConfigExecutor.scheduleConfigTask(new SelectMasterTask(), 10, 10, TimeUnit.SECONDS);
       }
       ConfigExecutor.scheduleConfigTask(new CheckDbHealthTask(), 10, 10, TimeUnit.SECONDS);
   }
}

在com.alibaba.nacos.config.server.service.datasource.ExternalDataSourceServiceImpl#reload中,我们可以看到

@Override
public synchronized void reload() throws IOException {
   try {
       // 根据配置文件,构建数据源集合
       dataSourceList = new ExternalDataSourceProperties()
           .build(EnvUtil.getEnvironment(), (dataSource) -> {
               JdbcTemplate jdbcTemplate = new JdbcTemplate();
               jdbcTemplate.setQueryTimeout(queryTimeout);
               jdbcTemplate.setDataSource(dataSource);
               testJtList.add(jdbcTemplate);
               isHealthList.add(Boolean.TRUE);
           });
       new SelectMasterTask().run();
       new CheckDbHealthTask().run();
   } catch (RuntimeException e) {
       FATAL_LOG.error(DB_LOAD_ERROR_MSG, e);
       throw new IOException(e);
   }
}

在com.alibaba.nacos.config.server.service.datasource.ExternalDataSourceProperties#build中

List<HikariDataSource> build(Environment environment, Callback<HikariDataSource> callback) {
   List<HikariDataSource> dataSources = new ArrayList<>();
   // 把胚子信息绑定到当前的ExternalDataSourceProperties对象,赋值操作
   // 因为外面是直接new出来的,需要对属性根据文件进行赋值
   Binder.get(environment).bind("db", Bindable.ofInstance(this));
   Preconditions.checkArgument(Objects.nonNull(num), "db.num is null");
   Preconditions.checkArgument(CollectionUtils.isNotEmpty(user), "db.user or db.user.[index] is null");
   Preconditions.checkArgument(CollectionUtils.isNotEmpty(password), "db.password or db.password.[index] is null");
   // 可以配置多个数据库
   for (int index = 0; index < num; index++) {
       int currentSize = index + 1;
       Preconditions.checkArgument(url.size() >= currentSize, "db.url.％s is null", index);
       // 拿到spring.datasource.xxx一堆,这个针对所有的数据源都适用
       DataSourcePoolProperties poolProperties = DataSourcePoolProperties.build(environment);
       // 为每一个数据源进行单独的url,user,password进行替换
       poolProperties.setDriverClassName(JDBC_DRIVER_NAME);
       poolProperties.setJdbcUrl(url.get(index).trim());
       poolProperties.setUsername(getOrDefault(user, index, user.get(0)).trim());
       poolProperties.setPassword(getOrDefault(password, index, password.get(0)).trim());
       HikariDataSource ds = poolProperties.getDataSource();
       ds.setConnectionTestQuery(TEST_QUERY);
       dataSources.add(ds);
       callback.accept(ds);
   }
   Preconditions.checkArgument(CollectionUtils.isNotEmpty(dataSources), "no datasource available");
   return dataSources;
}

这个整体还行,但是为啥JDBC_DRIVER_NAME是硬编码呢,代码中清晰看到

private static final String JDBC_DRIVER_NAME = "com.mysql.cj.jdbc.Driver";

到这已经一目了然,代码中硬编码了mysql,driver也没法改,所以根本没法更换数据库驱动,有点骚,而且com.mysql.cj.jdbc.Driver是mysql8的驱动,对mysql版本是有要求的

再看其他部分,也可以发现大量的硬编码,例如com.alibaba.nacos.config.server.auth.ExternalUserPersistServiceImpl

public class ExternalUserPersistServiceImpl implements UserPersistService {

@Autowired
   private ExternalStoragePersistServiceImpl persistService;

private JdbcTemplate jt;

@PostConstruct
   protected void init() {
       jt = persistService.getJdbcTemplate();
   }

/**
    * Execute create user operation.
    *
    * @param username username string value.
    * @param password password string value.
    */
   public void createUser(String username, String password) {
       String sql = "INSERT into users (username, password, enabled) VALUES (?, ?, ?)";

try {
           jt.update(sql, username, password, true);
       } catch (CannotGetJdbcConnectionException e) {
           LogUtil.FATAL_LOG.error("[db-error] " + e.toString(), e);
           throw e;
       }
   }

/**
    * Execute delete user operation.
    *
    * @param username username string value.
    */
   public void deleteUser(String username) {
       String sql = "DELETE from users WHERE username=?";
       try {
           jt.update(sql, username);
       } catch (CannotGetJdbcConnectionException e) {
           LogUtil.FATAL_LOG.error("[db-error] " + e.toString(), e);
           throw e;
       }
   }

/**
    * Execute update user password operation.
    *
    * @param username username string value.
    * @param password password string value.
    */
   public void updateUserPassword(String username, String password) {
       try {
           jt.update("UPDATE users SET password = ? WHERE username=?", password, username);
       } catch (CannotGetJdbcConnectionException e) {
           LogUtil.FATAL_LOG.error("[db-error] " + e.toString(), e);
           throw e;
       }
   }

/**
    * Execute find user by username operation.
    *
    * @param username username string value.
    * @return User model.
    */
   public User findUserByUsername(String username) {
       String sql = "SELECT username,password FROM users WHERE username=? ";
       try {
           return this.jt.queryForObject(sql, new Object[] {username}, USER_ROW_MAPPER);
       } catch (CannotGetJdbcConnectionException e) {
           LogUtil.FATAL_LOG.error("[db-error] " + e.toString(), e);
           throw e;
       } catch (EmptyResultDataAccessException e) {
           return null;
       } catch (Exception e) {
           LogUtil.FATAL_LOG.error("[db-other-error]" + e.getMessage(), e);
           throw new RuntimeException(e);
       }
   }

public Page<User> getUsers(int pageNo, int pageSize) {

PaginationHelper<User> helper = persistService.createPaginationHelper();

String sqlCountRows = "select count(*) from users where ";
       String sqlFetchRows = "select username,password from users where ";

String where = " 1=1 ";

try {
           Page<User> pageInfo = helper
                   .fetchPage(sqlCountRows + where, sqlFetchRows + where, new ArrayList<String>().toArray(), pageNo,
                           pageSize, USER_ROW_MAPPER);
           if (pageInfo == null) {
               pageInfo = new Page<>();
               pageInfo.setTotalCount(0);
               pageInfo.setPageItems(new ArrayList<>());
           }
           return pageInfo;
       } catch (CannotGetJdbcConnectionException e) {
           LogUtil.FATAL_LOG.error("[db-error] " + e.toString(), e);
           throw e;
       }
   }
   @Override
   public List<String> findUserLikeUsername(String username) {
       String sql = "SELECT username FROM users WHERE username like '％' ? '％'";
       List<String> users = this.jt.queryForList(sql, new String[]{username}, String.class);
       return users;
   }
}

几乎所有的sql都是硬编码....所以要改造成其他数据库工作量还是非常大的

来源：https://www.cnblogs.com/xixisix/p/15821706.html