SpringBoot druid配置datasource启动初始化数据库连接

1、问题场景：

1.1、服务在启动之后的第一笔或者几笔请求，处理时间较长，对于调用方来说超时，引发技术保底。

1.2、数据库连接信息配置错误，项目启动过程中却不产生任何异常，等到实际功能用到数据库了才抛出异常。
2、问题分析：
2.1、调用发系统通过http请求调用服务，设置超时时间为1s，超时时间过短，调整为3s；
2.2、应用启动之后的初始几笔请求处理时间过长，超过1s，跟踪日志发现在init-datasource中等待时间占用过多；
2.3、经过本地测试发现，在应用启动之后，在jvisualvm中查看mbeans中的druid.pool中的读写datasource的属性，启动之后的creatCount为0。在有请求进入之后才初始化了配置文件中的init连接数，导致了线上的问题；
3、解决方案：在数据库配置文件中配置读写datasource的bean中增加init-method=init的配置即可。druid官方文档中介绍，如果想要在项目启动的时候初始化配置的数据库连接数，需要显示配置或者调用init-method。

具体实现，如下图：

你可以在bean中增加init-method=init的配置，

也可以创建 dataSource 后，显示的调用 init 方法。

 附 init 方法源码：

    public void init() throws SQLException {
        if (inited) {
            return;
        }

        final ReentrantLock lock = this.lock;
        try {
            lock.lockInterruptibly();
        } catch (InterruptedException e) {
            throw new SQLException("interrupt", e);
        }

        boolean init = false;
        try {
            if (inited) {
                return;
            }

            initStackTrace = Utils.toString(Thread.currentThread().getStackTrace());

            this.id = DruidDriver.createDataSourceId();
            if (this.id > 1) {
                long delta = (this.id - 1) * 100000;
                this.connectionIdSeed.addAndGet(delta);
                this.statementIdSeed.addAndGet(delta);
                this.resultSetIdSeed.addAndGet(delta);
                this.transactionIdSeed.addAndGet(delta);
            }

            if (this.jdbcUrl != null) {
                this.jdbcUrl = this.jdbcUrl.trim();
                initFromWrapDriverUrl();
            }
            
            for (Filter filter : filters) {
                filter.init(this);
            }

            if (this.dbType == null || this.dbType.length() == 0) {
                this.dbType = JdbcUtils.getDbType(jdbcUrl, null);
            }

            if (JdbcConstants.MYSQL.equals(this.dbType) || //
                JdbcConstants.MARIADB.equals(this.dbType)) {
                boolean cacheServerConfigurationSet = false;
                if (this.connectProperties.containsKey("cacheServerConfiguration")) {
                    cacheServerConfigurationSet = true;
                } else if (this.jdbcUrl.indexOf("cacheServerConfiguration") != -1) {
                    cacheServerConfigurationSet = true;
                }
                if (cacheServerConfigurationSet) {
                    this.connectProperties.put("cacheServerConfiguration", "true");
                }
            }

            if (maxActive <= 0) {
                throw new IllegalArgumentException("illegal maxActive " + maxActive);
            }

            if (maxActive < minIdle) {
                throw new IllegalArgumentException("illegal maxActive " + maxActive);
            }

            if (getInitialSize() > maxActive) {
                throw new IllegalArgumentException("illegal initialSize " + this.initialSize + ", maxActieve " + maxActive);
            }

            if (timeBetweenLogStatsMillis > 0 && useGlobalDataSourceStat) {
                throw new IllegalArgumentException("timeBetweenLogStatsMillis not support useGlobalDataSourceStat=true");
            }
            
            if (maxEvictableIdleTimeMillis < minEvictableIdleTimeMillis) {
                throw new SQLException("maxEvictableIdleTimeMillis must be grater than minEvictableIdleTimeMillis");
            }

            if (this.driverClass != null) {
                this.driverClass = driverClass.trim();
            }

            initFromSPIServiceLoader();

            if (this.driver == null) {
                if (this.driverClass == null || this.driverClass.isEmpty()) {
                    this.driverClass = JdbcUtils.getDriverClassName(this.jdbcUrl);
                }

                if (MockDriver.class.getName().equals(driverClass)) {
                    driver = MockDriver.instance;
                } else {
                    driver = JdbcUtils.createDriver(driverClassLoader, driverClass);
                }
            } else {
                if (this.driverClass == null) {
                    this.driverClass = driver.getClass().getName();
                }
            }

            initCheck();

            initExceptionSorter();
            initValidConnectionChecker();
            validationQueryCheck();

            if (isUseGlobalDataSourceStat()) {
                dataSourceStat = JdbcDataSourceStat.getGlobal();
                if (dataSourceStat == null) {
                    dataSourceStat = new JdbcDataSourceStat("Global", "Global", this.dbType);
                    JdbcDataSourceStat.setGlobal(dataSourceStat);
                }
                if (dataSourceStat.getDbType() == null) {
                    dataSourceStat.setDbType(this.getDbType());
                }
            } else {
                dataSourceStat = new JdbcDataSourceStat(this.name, this.jdbcUrl, this.dbType, this.connectProperties);
            }
            dataSourceStat.setResetStatEnable(this.resetStatEnable);

            connections = new DruidConnectionHolder[maxActive];

            SQLException connectError = null;

            try {
                // init connections
                for (int i = 0, size = getInitialSize(); i < size; ++i) {
                    PhysicalConnectionInfo pyConnectInfo = createPhysicalConnection();
                    DruidConnectionHolder holder = new DruidConnectionHolder(this, pyConnectInfo);
                    connections[poolingCount] = holder;
                    incrementPoolingCount();
                }

                if (poolingCount > 0) {
                    poolingPeak = poolingCount;
                    poolingPeakTime = System.currentTimeMillis();
                }
            } catch (SQLException ex) {
                LOG.error("init datasource error, url: " + this.getUrl(), ex);
                connectError = ex;
            }

            createAndLogThread();
            createAndStartCreatorThread();
            createAndStartDestroyThread();

            initedLatch.await();
            init = true;

            initedTime = new Date();
            registerMbean();

            if (connectError != null && poolingCount == 0) {
                throw connectError;
            }
        } catch (SQLException e) {
            LOG.error("{dataSource-" + this.getID() + "} init error", e);
            throw e;
        } catch (InterruptedException e) {
            throw new SQLException(e.getMessage(), e);
        } finally {
            inited = true;
            lock.unlock();

            if (init && LOG.isInfoEnabled()) {
                LOG.info("{dataSource-" + this.getID() + "} inited");
            }
        }
    }

在 init 里调用 createPhysicalConnection() 创建物理连接

    public PhysicalConnectionInfo createPhysicalConnection() throws SQLException {
        String url = this.getUrl();
        Properties connectProperties = getConnectProperties();

        String user;
        if (getUserCallback() != null) {
            user = getUserCallback().getName();
        } else {
            user = getUsername();
        }

        String password = getPassword();
        PasswordCallback passwordCallback = getPasswordCallback();

        if (passwordCallback != null) {
            if (passwordCallback instanceof DruidPasswordCallback) {
                DruidPasswordCallback druidPasswordCallback = (DruidPasswordCallback) passwordCallback;

                druidPasswordCallback.setUrl(url);
                druidPasswordCallback.setProperties(connectProperties);
            }

            char[] chars = passwordCallback.getPassword();
            if (chars != null) {
                password = new String(chars);
            }
        }

        Properties physicalConnectProperties = new Properties();
        if (connectProperties != null) {
            physicalConnectProperties.putAll(connectProperties);
        }

        if (user != null && user.length() != 0) {
            physicalConnectProperties.put("user", user);
        }

        if (password != null && password.length() != 0) {
            physicalConnectProperties.put("password", password);
        }

        Connection conn;

        long connectStartNanos = System.nanoTime();
        long connectedNanos, initedNanos, validatedNanos;
        try {
            conn = createPhysicalConnection(url, physicalConnectProperties);
            connectedNanos = System.nanoTime();

            if (conn == null) {
                throw new SQLException("connect error, url " + url + ", driverClass " + this.driverClass);
            }

            initPhysicalConnection(conn);
            initedNanos = System.nanoTime();

            validateConnection(conn);
            validatedNanos = System.nanoTime();
            
            setCreateError(null);
        } catch (SQLException ex) {
            setCreateError(ex);
            throw ex;
        } catch (RuntimeException ex) {
            setCreateError(ex);
            throw ex;
        } catch (Error ex) {
            createErrorCount.incrementAndGet();
            throw ex;
        } finally {
            long nano = System.nanoTime() - connectStartNanos;
            createTimespan += nano;
        }

        return new PhysicalConnectionInfo(conn, connectStartNanos, connectedNanos, initedNanos, validatedNanos);
    }