Basic steps and mechanisms for MyBatis connection database configuration

Preface

MyBatis is a popular persistence layer framework that binds SQL statements, stored procedures, and Java methods by using XML or annotations, thus avoiding handwriting a large amount of JDBC code and manually setting parameters and result sets. Here are the basic steps and mechanisms for connecting to a database with MyBatis:

MyBatis source code version: 3.5.16

Example

<environments default="development">  
    <environment >  
        <transactionManager type="JDBC"/>  
        <dataSource type="POOLED">  
            <property name="driver" value="${}"/>  
            <property name="url" value="${}"/>  
            <property name="username" value="${}"/>  
            <property name="password" value="${}"/>  
        </dataSource>  
    </environment>  
</environments>

1. Read the configuration file

MyBatis byResourcesClass reads configuration files. Configuration files are usually in XML format, such as。

Key Code

String resource = "";
Reader reader = (resource)

2. Parsing the configuration file

SqlSessionFactoryBuilderuseXMLConfigBuilderParse the configuration file and convert the XML configuration into a Java object.

Key Code

SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);

XMLConfigBuilder parser = new XMLConfigBuilder(reader, environment, properties);

XMLConfigBuilder Source Code Snippet

private void parseConfiguration(XNode root) {  
  try {  
    // issue #117 Read the attribute first    propertiesElement(("properties"));  
    Properties settings = settingsAsProperties(("settings"));  
    loadCustomVfsImpl(settings);  
    loadCustomLogImpl(settings);  
    typeAliasesElement(("typeAliases"));  
    pluginsElement(("plugins"));  
    objectFactoryElement(("objectFactory"));  
    objectWrapperFactoryElement(("objectWrapperFactory"));  
    reflectorFactoryElement(("reflectorFactory"));  
    settingsElement(settings);  
    // read it after objectFactory and objectWrapperFactory issue #631  
    environmentsElement(("environments"));  
    databaseIdProviderElement(("databaseIdProvider"));  
    typeHandlersElement(("typeHandlers"));  
    mappersElement(("mappers"));  
  } catch (Exception e) {  
    throw new BuilderException("Error parsing SQL Mapper Configuration. Cause: " + e, e);  
  }  
}

XMLConfigBuilderparse XML configuration and generateConfigurationObject.

3. Create SqlSessionFactory

ConfigurationThe object contains all configuration information, including environment configuration, data source configuration, etc.SqlSessionFactoryBuilderuseConfigurationcreateDefaultSqlSessionFactory。

Key Code

public SqlSessionFactory build(Configuration config) {  
  return new DefaultSqlSessionFactory(config);  
}

4. Establish a database connection

DefaultSqlSessionFactoryCreateSqlSessionWhen, throughEnvironmentConfiguration andDataSourceGet the database connection.

DefaultSqlSessionFactory Source Code Snippet

public SqlSession openSession() {  
  return openSessionFromDataSource((), null, false);  
}

openSessionFromDataSourceIn the method,DataSourceUsed to obtain database connections.

Key Code

private SqlSession openSessionFromDataSource(ExecutorType execType, TransactionIsolationLevel level,  
    boolean autoCommit) {  
  //Environment configuration  final Environment environment = ();  
  //Business Factory  final TransactionFactory transactionFactory = getTransactionFactoryFromEnvironment(environment);  
  //Create a transaction  Transaction tx = ((), level, autoCommit);  
  //Create an executor  final Executor executor = (tx, execType);  
  //Return to SqlSession  return new DefaultSqlSession(configuration, executor, autoCommit);
}

5. Data source configuration

DataSourceConfigure inIn the file, throughDataSourceFactoryCreate a specific data source instance.

Key Code

// Obtain the data source factoryString type = ("type");  
Properties props = ();  
DataSourceFactory factory = (DataSourceFactory) resolveClass(type).getDeclaredConstructor().newInstance();  
(props);    
// Get the data sourceDataSource dataSource = ();

Summarize

The steps to connect to the MyBatis database include:

Read configuration files:passResourcesClass reads XML files.
Parse configuration files:useXMLConfigBuilderparse XML, generateConfigurationObject.
Create SqlSessionFactory:useSqlSessionFactoryBuilderandConfigurationcreateDefaultSqlSessionFactory。
Establish a database connection：DefaultSqlSessionFactorycreateSqlSession,useDataSourceGet the database connection.

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