这里，首先想说的是，现在的web应用，处理的数据对象，有结构化的，也有非结构化的。同时存在。但是在spring-boot操作数据库的时候，若是在properties文件中配置数据源的信息，通过默认配置加载数据源的话，往往只会启动一个。

我出于想弄清如何配置数据源的目的，在这里demo一个配置两个数据源的例子。分别是mysql和mongo。mysql的持久化采用的是mybatis。

mongo的操作比较简单，直接贴上配置数据库的代码：

 package com.shihuc.dbconn.sourceconfig.mongo;

 import java.util.Arrays;

 import org.springframework.beans.factory.annotation.Value;

 import org.springframework.boot.autoconfigure.EnableAutoConfiguration;

 import org.springframework.boot.autoconfigure.mongo.MongoAutoConfiguration;

 import org.springframework.boot.autoconfigure.mongo.MongoDataAutoConfiguration;

 import org.springframework.context.annotation.Bean;

 import org.springframework.context.annotation.ComponentScan;

 import org.springframework.context.annotation.Configuration;

 import org.springframework.data.mongodb.config.AbstractMongoConfiguration;

 import org.springframework.data.mongodb.repository.config.EnableMongoRepositories;

 import com.mongodb.Mongo;

 import com.mongodb.MongoClient;

 import com.mongodb.MongoCredential;

 import com.mongodb.ServerAddress;

 import com.mongodb.WriteConcern;

 @Configuration

 @EnableAutoConfiguration(exclude={MongoAutoConfiguration.class, MongoDataAutoConfiguration.class})

 @ComponentScan

 @EnableMongoRepositories

 public class MongoDataSourceConfig extends AbstractMongoConfiguration{

     @Value("${mongo.database}")

     private String dbname;

     @Value("${mongo.host}")

     private String dbhost;

     @Value("${mongo.port}")

     private String dbport;

     @Value("${mongo.username}")

     private String username;

     @Value("${mongo.password}")

     private String password;

     @Override

     protected String getDatabaseName() {

         return this.dbname;

     }

     public MongoDataSourceConfig(){

         if(null == dbport || "".equalsIgnoreCase(dbport.trim())){

             dbport = "27017";

         }

     }

     @Override

     @Bean(name = "mongods")

     public Mongo mongo() throws Exception {

         ServerAddress serverAdress = new  ServerAddress(dbhost, Integer.valueOf(dbport));

         MongoCredential credential = MongoCredential.createMongoCRCredential(username, dbname , password.toCharArray());

         //Do not use new Mongo(), is deprecated.

         Mongo mongo =  new MongoClient(serverAdress, Arrays.asList(credential));

         mongo.setWriteConcern(WriteConcern.SAFE);

         return mongo;

     }

 }

mongo数据库配置继承AbstractMongoConfiguration，在这个过程中，会向spring容器注册一个mongoTemplate，这个很重要，后期操作mongo数据库时，主要靠它。

这里重点说下spring-boot和mybatis集成操作mysql的配置和注意事项。

 package com.shihuc.dbconn.sourceconfig.mysql;

 import javax.sql.DataSource;

 import org.springframework.beans.factory.annotation.Value;

 import org.springframework.boot.autoconfigure.EnableAutoConfiguration;

 import org.springframework.boot.autoconfigure.jdbc.DataSourceAutoConfiguration;

 import org.springframework.context.annotation.Bean;

 import org.springframework.context.annotation.Configuration;

 import org.springframework.jdbc.datasource.DriverManagerDataSource;

 @Configuration

 @EnableAutoConfiguration(exclude = {DataSourceAutoConfiguration.class})

 public class MysqlDataSourceConfig {

     @Value("${mysql.driver}")

     private String driver;

     @Value("${mysql.url}")

     private String url;

     @Value("${mysql.username}")

     private String username;

     @Value("${mysql.password}")

     private String password;

     @Bean(name="mysqlds")

     public DataSource mysql()

     {

         DriverManagerDataSource ds = new DriverManagerDataSource();

         ds.setDriverClassName(driver);

         ds.setUrl(url);

         ds.setUsername(username);

         ds.setPassword(password);

         return ds;

     }

 }

这个是datasource的配置，注意，类似mongo的配置，要将自动配置的类给exclude掉。让spring只处理我们希望的数据源。否则会受到classpath下的信息，干扰数据源的配置。

另外，就是mybatis的配置。由于spring-boot重点特色是纯java config，所以，这里也采用java配置和注解启用mybatis。

 package com.shihuc.dbconn.sourceconfig.mysql;

 import javax.sql.DataSource;

 import org.apache.ibatis.session.SqlSessionFactory;

 import org.mybatis.spring.SqlSessionFactoryBean;

 import org.mybatis.spring.annotation.MapperScan;

 import org.springframework.beans.factory.annotation.Autowired;

 import org.springframework.beans.factory.annotation.Qualifier;

 import org.springframework.context.annotation.Bean;

 import org.springframework.context.annotation.Configuration;

 @Configuration

 @MapperScan(basePackages = "com.shihuc.dbconn.dao.mysql")

 public class MysqlMybatisConfig {

     @Autowired

     @Qualifier("mysqlds")

     private DataSource mysqlds;

     @Bean

     public SqlSessionFactory sqlSessionFactoryBean() throws Exception {

         final SqlSessionFactoryBean sessionFactory = new SqlSessionFactoryBean();

         sessionFactory.setDataSource(mysqlds);

         return sessionFactory.getObject();

     }

 }

这里，mapperscan主要是为配置JavaBean和持久化对象之间的映射关系设定根路径。在这个例子中，mapper部分，其实就是通过insert,delete,update,select等注解，结合具体的SQL语句实现ORM的关系。看看这里的代码：

 package com.shihuc.dbconn.dao.mysql;

 import org.apache.ibatis.annotations.Insert;

 import org.apache.ibatis.annotations.Select;

 import com.shihuc.dbconn.pojo.mysql.MysqlUser;

 public interface IMysqlUser {

     @Select("SELECT * FROM user WHERE id = #{userId}")

     public MysqlUser getUser(int userId);

     @Insert("insert into user (username, job, age, hometown) values(#{username}, #{job}, #{age}, #{hometown})")

     public int addUser(MysqlUser user);

 }

另外，配合这个IMysqlUser使用的MysqlUser的定义也很重要，主要是里面的constructor函数，通常，添加数据，比如上面的addUser操作，是要创建一个POJO的对象，为了方便，一般都会创建一个带参数的构造函数，注意，必须也同时创建一个无参数的构造函数，否则，在做查询操作，比如上面的getUser时，会出现下面的错误：

   .   ____          _            __ _ _

  /\\ / ___'_ __ _ _(_)_ __  __ _ \ \ \ \

 ( ( )\___ | '_ | '_| | '_ \/ _` | \ \ \ \

  \\/  ___)| |_)| | | | | || (_| |  ) ) ) )

   '  |____| .__|_| |_|_| |_\__, | / / / /

  =========|_|==============|___/=/_/_/_/

  :: Spring Boot ::        (v1.2.7.RELEASE)

 2016-01-29 15:01:07.930  INFO 30880 --- [           main] com.shihuc.dbconn.DbConnApp              : Starting DbConnApp on CloudGame with PID 30880 (/home/webWps/dbconn/target/classes started by root in /home/webWps/dbconn)

 2016-01-29 15:01:07.997  INFO 30880 --- [           main] s.c.a.AnnotationConfigApplicationContext : Refreshing org.springframework.context.annotation.AnnotationConfigApplicationContext@a85aa40: startup date [Fri Jan 29 15:01:07 CST 2016]; root of context hierarchy

 2016-01-29 15:01:09.887  INFO 30880 --- [           main] trationDelegate$BeanPostProcessorChecker : Bean 'mysqlDataSourceConfig' of type [class com.shihuc.dbconn.sourceconfig.mysql.MysqlDataSourceConfig$$EnhancerBySpringCGLIB$$63c6820a] is not eligible for getting processed by all BeanPostProcessors (for example: not eligible for auto-proxying)

 2016-01-29 15:01:09.915  INFO 30880 --- [           main] o.s.j.d.DriverManagerDataSource          : Loaded JDBC driver: com.mysql.jdbc.Driver

 2016-01-29 15:01:09.923  INFO 30880 --- [           main] trationDelegate$BeanPostProcessorChecker : Bean 'mysqlds' of type [class org.springframework.jdbc.datasource.DriverManagerDataSource] is not eligible for getting processed by all BeanPostProcessors (for example: not eligible for auto-proxying)

 2016-01-29 15:01:09.926  INFO 30880 --- [           main] trationDelegate$BeanPostProcessorChecker : Bean 'mysqlMybatisConfig' of type [class com.shihuc.dbconn.sourceconfig.mysql.MysqlMybatisConfig$$EnhancerBySpringCGLIB$$bbfde9e4] is not eligible for getting processed by all BeanPostProcessors (for example: not eligible for auto-proxying)

 2016-01-29 15:01:09.991  INFO 30880 --- [           main] trationDelegate$BeanPostProcessorChecker : Bean 'sqlSessionFactoryBean' of type [class org.apache.ibatis.session.defaults.DefaultSqlSessionFactory] is not eligible for getting processed by all BeanPostProcessors (for example: not eligible for auto-proxying)

 2016-01-29 15:01:10.040  INFO 30880 --- [           main] trationDelegate$BeanPostProcessorChecker : Bean 'IMysqlUser' of type [class org.mybatis.spring.mapper.MapperFactoryBean] is not eligible for getting processed by all BeanPostProcessors (for example: not eligible for auto-proxying)

 2016-01-29 15:01:10.876  INFO 30880 --- [           main] o.s.j.e.a.AnnotationMBeanExporter        : Registering beans for JMX exposure on startup

 2016-01-29 15:01:10.888  INFO 30880 --- [           main] com.shihuc.dbconn.DbConnApp              : Started DbConnApp in 3.274 seconds (JVM running for 3.561)

 Exception in thread "main" org.mybatis.spring.MyBatisSystemException: nested exception is org.apache.ibatis.reflection.ReflectionException: Error instantiating class com.shihuc.dbconn.pojo.mysql.MysqlUser with invalid types () or values (). Cause: java.lang.NoSuchMethodException: com.shihuc.dbconn.pojo.mysql.MysqlUser.<init>()

     at org.mybatis.spring.MyBatisExceptionTranslator.translateExceptionIfPossible(MyBatisExceptionTranslator.java:75)

     at org.mybatis.spring.SqlSessionTemplate$SqlSessionInterceptor.invoke(SqlSessionTemplate.java:371)

     at com.sun.proxy.$Proxy26.selectOne(Unknown Source)

     at org.mybatis.spring.SqlSessionTemplate.selectOne(SqlSessionTemplate.java:163)

     at org.apache.ibatis.binding.MapperMethod.execute(MapperMethod.java:63)

     at org.apache.ibatis.binding.MapperProxy.invoke(MapperProxy.java:43)

     at com.sun.proxy.$Proxy34.getUser(Unknown Source)

     at com.shihuc.dbconn.service.mysql.MysqlUserService.getUser(MysqlUserService.java:20)

     at com.shihuc.dbconn.DbConnApp.main(DbConnApp.java:34)

 Caused by: org.apache.ibatis.reflection.ReflectionException: Error instantiating class com.shihuc.dbconn.pojo.mysql.MysqlUser with invalid types () or values (). Cause: java.lang.NoSuchMethodException: com.shihuc.dbconn.pojo.mysql.MysqlUser.<init>()

     at org.apache.ibatis.reflection.factory.DefaultObjectFactory.instantiateClass(DefaultObjectFactory.java:83)

     at org.apache.ibatis.reflection.factory.DefaultObjectFactory.create(DefaultObjectFactory.java:45)

     at org.apache.ibatis.reflection.factory.DefaultObjectFactory.create(DefaultObjectFactory.java:38)

     at org.apache.ibatis.executor.resultset.DefaultResultSetHandler.createResultObject(DefaultResultSetHandler.java:530)

     at org.apache.ibatis.executor.resultset.DefaultResultSetHandler.createResultObject(DefaultResultSetHandler.java:509)

     at org.apache.ibatis.executor.resultset.DefaultResultSetHandler.getRowValue(DefaultResultSetHandler.java:329)

     at org.apache.ibatis.executor.resultset.DefaultResultSetHandler.handleRowValuesForSimpleResultMap(DefaultResultSetHandler.java:289)

     at org.apache.ibatis.executor.resultset.DefaultResultSetHandler.handleRowValues(DefaultResultSetHandler.java:264)

     at org.apache.ibatis.executor.resultset.DefaultResultSetHandler.handleResultSet(DefaultResultSetHandler.java:234)

     at org.apache.ibatis.executor.resultset.DefaultResultSetHandler.handleResultSets(DefaultResultSetHandler.java:152)

     at org.apache.ibatis.executor.statement.PreparedStatementHandler.query(PreparedStatementHandler.java:57)

     at org.apache.ibatis.executor.statement.RoutingStatementHandler.query(RoutingStatementHandler.java:70)

     at org.apache.ibatis.executor.SimpleExecutor.doQuery(SimpleExecutor.java:57)

     at org.apache.ibatis.executor.BaseExecutor.queryFromDatabase(BaseExecutor.java:259)

     at org.apache.ibatis.executor.BaseExecutor.query(BaseExecutor.java:132)

     at org.apache.ibatis.executor.CachingExecutor.query(CachingExecutor.java:105)

     at org.apache.ibatis.executor.CachingExecutor.query(CachingExecutor.java:81)

     at org.apache.ibatis.session.defaults.DefaultSqlSession.selectList(DefaultSqlSession.java:104)

     at org.apache.ibatis.session.defaults.DefaultSqlSession.selectList(DefaultSqlSession.java:98)

     at org.apache.ibatis.session.defaults.DefaultSqlSession.selectOne(DefaultSqlSession.java:62)

     at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)

     at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)

     at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)

     at java.lang.reflect.Method.invoke(Method.java:606)

     at org.mybatis.spring.SqlSessionTemplate$SqlSessionInterceptor.invoke(SqlSessionTemplate.java:358)

     ... 7 more

 Caused by: java.lang.NoSuchMethodException: com.shihuc.dbconn.pojo.mysql.MysqlUser.<init>()

     at java.lang.Class.getConstructor0(Class.java:2892)

     at java.lang.Class.getDeclaredConstructor(Class.java:2058)

     at org.apache.ibatis.reflection.factory.DefaultObjectFactory.instantiateClass(DefaultObjectFactory.java:57)

     ... 31 more

 2016-01-29 15:01:11.139  INFO 30880 --- [       Thread-1] s.c.a.AnnotationConfigApplicationContext : Closing org.springframework.context.annotation.AnnotationConfigApplicationContext@a85aa40: startup date [Fri Jan 29 15:01:07 CST 2016]; root of context hierarchy

 2016-01-29 15:01:11.142  INFO 30880 --- [       Thread-1] o.s.j.e.a.AnnotationMBeanExporter        : Unregistering JMX-exposed beans on shutdown

方便说明问题，将MysqlUser也附上代码：

 package com.shihuc.dbconn.pojo.mysql;

 import com.shihuc.dbconn.pojo.User;

 public class MysqlUser extends User{

     private static final long serialVersionUID = -6412107575129572581L;

     //这个id是数据库中通过设置auto_increment得到的主键值

     private int id;

     public int getId() {

         return id;

     }

     public void setId(int id) {

         this.id = id;

     }

     public MysqlUser(){

     }

     public MysqlUser(String username, String job, int age, String hometown){

         this.username = username;

         this.job = job;

         this.age = age;

         this.hometown = hometown;

     }

 }

下面看看，测试程序吧，我是在main函数里面写的，如下：

 package com.shihuc.dbconn;

 import org.springframework.boot.SpringApplication;

 import org.springframework.boot.autoconfigure.SpringBootApplication;

 import org.springframework.context.ApplicationContext;

 import org.springframework.context.annotation.PropertySource;

 import com.shihuc.dbconn.pojo.mongo.MongoUser;

 import com.shihuc.dbconn.pojo.mysql.MysqlUser;

 import com.shihuc.dbconn.service.mongo.MongoUserService;

 import com.shihuc.dbconn.service.mysql.MysqlUserService;

 /**

  *

  * @author  shihuc

  * @date    Jan 29, 2016

  *

  */

 @SpringBootApplication

 @PropertySource(value = "dbconn.properties")

 public class DbConnApp

 {

        public static void main(String[] args) throws Throwable {

         SpringApplication app = new SpringApplication(DbConnApp.class);

         ApplicationContext ctx = app.run(args);        

         MysqlUserService mysqlUserService = (MysqlUserService)ctx.getBean("mysqlUserService");

 //        MysqlUser su = new MysqlUser("shihuc", "SW", 30 , "wuhan");

 //        mysqlUserService.addUser(su);

         MysqlUser ue = mysqlUserService.getUser(1);

         System.out.println("Mysql User: " + ue);        

         MongoUserService mongoUserService = (MongoUserService)ctx.getBean("mongoUserService");

 //        MongoUser mu = new MongoUser("shihuc", "SW", 30 , "wuhan");

 //        mongoUserService.addUser(mu);

         MongoUser um = mongoUserService.getUser("shihuc");

         System.out.println("Mongo User: " + um);

     }

 }

最后附上我的maven项目的pom文件：

 <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.shihuc</groupId>

   <artifactId>dbconn</artifactId>

   <version>0.0.1-SNAPSHOT</version>

   <packaging>jar</packaging>

   <name>dbconn</name>

   <url>http://maven.apache.org</url>

   <parent>

         <groupId>org.springframework.boot</groupId>

         <artifactId>spring-boot-starter-parent</artifactId>

         <version>1.2.7.RELEASE</version>

   </parent>

   <properties>

     <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>

   </properties>

   <dependencies>

       <dependency>

           <groupId>org.springframework.boot</groupId>

         <artifactId>spring-boot-starter-jdbc</artifactId>

     </dependency>

     <dependency>

         <groupId>mysql</groupId>

         <artifactId>mysql-connector-java</artifactId>

         </dependency>

     <dependency>

         <groupId>org.mybatis</groupId>

         <artifactId>mybatis</artifactId>

         <version>3.2.3</version>

     </dependency>

     <dependency>

         <groupId>org.mybatis</groupId>

         <artifactId>mybatis-spring</artifactId>

         <version>1.2.2</version>

     </dependency>

     <dependency>

         <groupId>org.springframework.boot</groupId>

         <artifactId>spring-boot-starter-data-mongodb</artifactId>

     </dependency>

   </dependencies>

   <build>

     <plugins>

         <plugin>

             <groupId>org.springframework.boot</groupId>

             <artifactId>spring-boot-maven-plugin</artifactId>

         </plugin>

     </plugins>

   </build>

 </project>

还是相对比较简单的配置和操作。对于这个demo的例子程序，可以在GitHub https://github.com/shihuc/dbconn上下载。

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