資料庫連線池之坑

通常我們使用資料庫時會使用第三方的資料庫連線池，在這裡我使用了

   <dependency>
            <groupId>com.alibaba</groupId>
            <artifactId>druid-spring-boot-starter</artifactId>
            <version>${druid-version}</version>
   </dependency>

這裡存在版本問題報錯，這裡先貼上完整可用的pom檔案範例

<?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>

    <groupId
 
>com.chineseall</groupId>
    <artifactId>jump-chain-process</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <packaging>jar</packaging>

    <name>jump-chain-process</name>
    <description>Demo project for Spring Boot</description>
 


    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.0.4.RELEASE</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>

    <properties>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
        <java.version>1.8</java.version>

        <mybatis-springboot-version>1.3.1</mybatis-springboot-version>
        <mysql-version>5.1.38</mysql-version>
        <druid-version>1.1.10</druid-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-test</artifactId>
            <scope>test</scope>
        </dependency>

        <!--資料庫相關-->
        <dependency>
            <groupId>org.mybatis.spring.boot</groupId>
            <artifactId>mybatis-spring-boot-starter</artifactId>
            <version>${mybatis-springboot-version}</version>
        </dependency>
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>${mysql-version}</version><!--$NO-MVN-MAN-VER$-->
        </dependency>
        <!-- alibaba的druid資料庫連線池 -->
        <dependency>
            <groupId>com.alibaba</groupId>
            <artifactId>druid-spring-boot-starter</artifactId>
            <version>${druid-version}</version>
        </dependency>

    </dependencies>

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


</project>

這裡注意阿里連結池的版本是1.1.10是沒有問題的

 <druid-version>1.1.10</druid-version>

在使用1.1.2時報錯

Caused by: java.lang.NoClassDefFoundError: org/springframework/boot/autoconfigure/jdbc/metadata/DataSourcePoolMetadataProvider
    at java.lang.Class.getDeclaredMethods0(Native Method) ~[na:1.8.0_151]
    at java.lang.Class.privateGetDeclaredMethods(Class.java:2701) ~[na:1.8.0_151]
    at java.lang.Class.getDeclaredMethods(Class.java:1975) ~[na:1.8.0_151]
    at org.springframework.util.ReflectionUtils.getDeclaredMethods(ReflectionUtils.java:641) ~[spring-core-5.0.8.RELEASE.jar:5.0.8.RELEASE]
    ... 20 common frames omitted
Caused by: java.lang.ClassNotFoundException: org.springframework.boot.autoconfigure.jdbc.metadata.DataSourcePoolMetadataProvider
    at java.net.URLClassLoader.findClass(URLClassLoader.java:381) ~[na:1.8.0_151]
    at java.lang.ClassLoader.loadClass(ClassLoader.java:424) ~[na:1.8.0_151]
    at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:335) ~[na:1.8.0_151]
    at java.lang.ClassLoader.loadClass(ClassLoader.java:357) ~[na:1.8.0_151]
    ... 24 common frames omitted

遇到這類問題果斷換版本吧建議使用1.1.10
如果使用其他資料庫連結池出現類似錯誤建議升級版本

Mybatis對映問題

下滑線對映需要進行配置
下面貼出我使用的application.yml以及mybatis.xml配置
application.yml

server:
    tomcat:
        uri-encoding: UTF-8
        max-threads: 1000
        min-spare-threads: 30
    port: 8888

spring:
    datasource:
        # 使用druid資料來源
        type: com.alibaba.druid.pool.DruidDataSource
        driverClassName: com.mysql.jdbc.Driver
        druid:
            url: jdbc:mysql://yoururl
            username: root
            password: root
            initial-size: 10
            max-active: 100
            min-idle: 10
            max-wait: 60000
            pool-prepared-statements: true
            max-pool-prepared-statement-per-connection-size: 20
            time-between-eviction-runs-millis: 60000
            min-evictable-idle-time-millis: 300000
            validation-query: SELECT 1 FROM DUAL
            test-while-idle: true
            test-on-borrow: false
            test-on-return: false
            stat-view-servlet:
                enabled: true
                url-pattern: /druid/*
                #login-username: admin
                #login-password: admin
            filter:
                stat:
                    log-slow-sql: true
                    slow-sql-millis: 1000
                    merge-sql: true
                wall:
                    config:
                        multi-statement-allow: true
mybatis:
  mapper-locations: classpath:mapper/*.xml  #注意：一定要對應mapper對映xml檔案的所在路徑
  type-aliases-package: com.xxx.xxx.bean  # 注意：對應實體類的路徑
  configLocation: classpath:mybatis.xml #mybatis 配置檔案路徑

mybatis.xml

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE configuration PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
        "http://mybatis.org/dtd/mybatis-3-config.dtd">
<configuration>



    <!-- 配置mybatis的快取，延遲載入等等一系列屬性 -->
    <settings>

        <!-- 全域性對映器啟用快取 -->
        <setting name="cacheEnabled" value="true"/>

        <!-- 查詢時，關閉關聯物件即時載入以提高效能 -->
        <setting name="lazyLoadingEnabled" value="true"/>

        <!-- 對於未知的SQL查詢，允許返回不同的結果集以達到通用的效果 -->
        <setting name="multipleResultSetsEnabled" value="true"/>

        <!-- 允許使用列標籤代替列名 -->
        <setting name="useColumnLabel" value="true"/>

        <!-- 不允許使用自定義的主鍵值(比如由程式生成的UUID 32位編碼作為鍵值)，資料表的PK生成策略將被覆蓋 -->
        <setting name="useGeneratedKeys" value="false"/>

        <!-- 給予被巢狀的resultMap以欄位-屬性的對映支援 FULL,PARTIAL -->
        <setting name="autoMappingBehavior" value="PARTIAL"/>

        <!-- 對於批量更新操作快取SQL以提高效能 BATCH,SIMPLE -->
        <!-- <setting name="defaultExecutorType" value="BATCH" /> -->

        <!-- 資料庫超過25000秒仍未響應則超時 -->
        <!-- <setting name="defaultStatementTimeout" value="25000" /> -->

        <!-- Allows using RowBounds on nested statements -->
        <setting name="safeRowBoundsEnabled" value="false"/>

        <!-- Enables automatic mapping from classic database column names A_COLUMN to camel case classic Java property names aColumn. -->
        <setting name="mapUnderscoreToCamelCase" value="true"/>

        <!-- MyBatis uses local cache to prevent circular references and speed up repeated nested queries. By default (SESSION) all queries executed during a session are cached. If localCacheScope=STATEMENT 
            local session will be used just for statement execution, no data will be shared between two different calls to the same SqlSession. -->
        <setting name="localCacheScope" value="SESSION"/>

        <!-- Specifies the JDBC type for null values when no specific JDBC type was provided for the parameter. Some drivers require specifying the column JDBC type but others work with generic values 
            like NULL, VARCHAR or OTHER. -->
        <setting name="jdbcTypeForNull" value="OTHER"/>

        <!-- Specifies which Object's methods trigger a lazy load -->
        <setting name="lazyLoadTriggerMethods" value="equals,clone,hashCode,toString"/>

        <!-- 設定關聯物件載入的形態，此處為按需載入欄位(載入欄位由SQL指 定)，不會載入關聯表的所有欄位，以提高效能 -->
        <setting name="aggressiveLazyLoading" value="false"/>

    </settings>



</configuration>

此條為開啟對映

        <setting name="mapUnderscoreToCamelCase" value="true"/>

主從庫之坑

在配置主從庫時若還以平常方式連結資料庫，在啟動專案時會報以下錯誤

***************************
APPLICATION FAILED TO START
***************************

Description:

Failed to configure a DataSource: 'url' attribute is not specified and no embedded datasource could be configured.

Reason: Failed to determine a suitable driver class


Action:

Consider the following:
    If you want an embedded database (H2, HSQL or Derby), please put it on the classpath.
    If you have database settings to be loaded from a particular profile you may need to activate it (no profiles are currently active).

yml

   masterDataSource:  #主庫資料來源
                url: jdbc:mysql://yoururl
                username: root
                password: root
   slaveDataSource:  #從庫資料來源
                url: yoururl
                username: root
                password: root

多資料來源需要進行特殊配置，配置方法這裡以後會補全，(這裡暫只說明錯誤根源)