Spring JDBC數據源分析

時間 2019-11-26

原文原文鏈接

Spring數據源分析

Spring自帶數據源DriverManagerDataSource

Spring自己提供了一個簡單的數據源實現類DriverManagerDataSource ，它位於org.springframework.jdbc.datasource包中。這個類實現了javax.sql.DataSource接口，但它並無提供池化鏈接的機制，每次調用getConnection()獲取新鏈接時，只是簡單地建立一個新的鏈接。所以，這個數據源類比較適合在單元測試或簡單的獨立應用中使用，由於它不須要額外的依賴類。分析這樣一段代碼:java

package com.jason.spring.datasource.jdbc;

import org.springframework.context.support.ClassPathXmlApplicationContext;
import org.springframework.jdbc.core.JdbcTemplate;
import org.springframework.transaction.TransactionStatus;
import org.springframework.transaction.support.TransactionCallbackWithoutResult;
import org.springframework.transaction.support.TransactionTemplate;

import javax.sql.DataSource;
import java.util.List;
import java.util.Map;
public class TestSpringJDBC {

    public static void main(String[] args) {
        final ClassPathXmlApplicationContext applicationContext = new ClassPathXmlApplicationContext("spring/spring-jdbc.xml");
        final DataSource dataSource = (DataSource) applicationContext.getBean("jdbcDataSource");
        TransactionTemplate transactionTemplate = (TransactionTemplate) applicationContext.getBean("transactionTemplate");
        try {
            JdbcTemplate jdbcTemplate = new JdbcTemplate(dataSource);
            List<Map<String, Object>> map = jdbcTemplate.queryForList("select * from test.order for update ");
            System.out.println(map);
            transactionTemplate.execute(new TransactionCallbackWithoutResult() {

                @Override
                protected void doInTransactionWithoutResult(TransactionStatus status) {
                    try {
                        JdbcTemplate jdbcTemplate = (JdbcTemplate)applicationContext.getBean("jdbcTemplate");
                        List<Map<String, Object>> map = jdbcTemplate.queryForList("select * from test.order for update ");
                        System.out.println(map);
                    } catch (Exception e) {
                        status.setRollbackOnly();
                    }
                }
            });
            //System.in.read();

        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

對應的spring的配置文件:mysql

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:dubbo="http://code.alibabatech.com/schema/dubbo"
       xsi:schemaLocation="http://www.springframework.org/schema/beans
						http://www.springframework.org/schema/beans/spring-beans.xsd http://code.alibabatech.com/schema/dubbo http://code.alibabatech.com/schema/dubbo/dubbo.xsd">
   <bean id="jdbcDataSource" class="org.springframework.jdbc.datasource.DriverManagerDataSource">
       <property name="driverClassName" value="com.mysql.jdbc.Driver"/>
       <property name="url" value="jdbc:mysql://localhost:3306/test"/>
       <property name="username" value="root"/>
       <property name="password" value="root"/>
   </bean>
    <bean id="jdbcTemplate" class="org.springframework.jdbc.core.JdbcTemplate">
        <property name="dataSource" ref="jdbcDataSource"/>
    </bean>
    <bean id="dataSourceTransactionManager" class="org.springframework.jdbc.datasource.DataSourceTransactionManager">
        <property name="dataSource" ref="jdbcDataSource"/>
    </bean>
    <bean id="transactionTemplate" class="org.springframework.transaction.support.TransactionTemplate">
        <property name="transactionManager" ref="dataSourceTransactionManager"/>
        <property name="isolationLevelName" value="ISOLATION_DEFAULT"/>
    </bean>

</beans>

會執行到JdbcTemplate中的以下方法：spring

public <T> T execute(StatementCallback<T> action) throws DataAccessException {
		Assert.notNull(action, "Callback object must not be null");

		Connection con = DataSourceUtils.getConnection(getDataSource());
		Statement stmt = null;
		try {
			Connection conToUse = con;
			if (this.nativeJdbcExtractor != null &&
					this.nativeJdbcExtractor.isNativeConnectionNecessaryForNativeStatements()) {
				conToUse = this.nativeJdbcExtractor.getNativeConnection(con);
			}
			stmt = conToUse.createStatement();
			applyStatementSettings(stmt);
			Statement stmtToUse = stmt;
			if (this.nativeJdbcExtractor != null) {
				stmtToUse = this.nativeJdbcExtractor.getNativeStatement(stmt);
			}
			T result = action.doInStatement(stmtToUse);
			handleWarnings(stmt);
			return result;
		}
		catch (SQLException ex) {
			// Release Connection early, to avoid potential connection pool deadlock
			// in the case when the exception translator hasn't been initialized yet.
			JdbcUtils.closeStatement(stmt);
			stmt = null;
			DataSourceUtils.releaseConnection(con, getDataSource());
			con = null;
			throw getExceptionTranslator().translate("StatementCallback", getSql(action), ex);
		}
		finally {
			JdbcUtils.closeStatement(stmt);
			DataSourceUtils.releaseConnection(con, getDataSource());
		}
	}

從該段代碼能夠看到，其Connection 是經過DataSourceUtils.getConnection(getDataSource())去拿到的，繼續跟進去：會到org.springframework.jdbc.datasource.DataSourceUtils中的：sql

public static Connection doGetConnection(DataSource dataSource) throws SQLException {
		Assert.notNull(dataSource, "No DataSource specified");

		ConnectionHolder conHolder = (ConnectionHolder) TransactionSynchronizationManager.getResource(dataSource);
		if (conHolder != null && (conHolder.hasConnection() || conHolder.isSynchronizedWithTransaction())) {
			conHolder.requested();
			if (!conHolder.hasConnection()) {
				logger.debug("Fetching resumed JDBC Connection from DataSource");
				conHolder.setConnection(dataSource.getConnection());
			}
			return conHolder.getConnection();
		}
		// Else we either got no holder or an empty thread-bound holder here.

		logger.debug("Fetching JDBC Connection from DataSource");
		Connection con = dataSource.getConnection();

		if (TransactionSynchronizationManager.isSynchronizationActive()) {
			logger.debug("Registering transaction synchronization for JDBC Connection");
			// Use same Connection for further JDBC actions within the transaction.
			// Thread-bound object will get removed by synchronization at transaction completion.
			ConnectionHolder holderToUse = conHolder;
			if (holderToUse == null) {
				holderToUse = new ConnectionHolder(con);
			}
			else {
				holderToUse.setConnection(con);
			}
			holderToUse.requested();
			TransactionSynchronizationManager.registerSynchronization(
					new ConnectionSynchronization(holderToUse, dataSource));
			holderToUse.setSynchronizedWithTransaction(true);
			if (holderToUse != conHolder) {
				TransactionSynchronizationManager.bindResource(dataSource, holderToUse);
			}
		}

		return con;
	}

在資源釋放時，會有區別：無事務時，直接釋放數據源，有事務時，暫時不真正的釋放數據源app

public static void doReleaseConnection(Connection con, DataSource dataSource) throws SQLException {
		if (con == null) {
			return;
		}
		if (dataSource != null) {
			ConnectionHolder conHolder = (ConnectionHolder) TransactionSynchronizationManager.getResource(dataSource);
			if (conHolder != null && connectionEquals(conHolder, con)) {
				// It's the transactional Connection: Don't close it.
				conHolder.released();
				return;
			}
		}
		logger.debug("Returning JDBC Connection to DataSource");
		doCloseConnection(con, dataSource);
	}