正文
我们上篇文章讲到了查询方法里面的doQuery方法，这里面就是调用JDBC的API了，其中的逻辑比较复杂，我们这边文章来讲，先看看我们上篇文章分析的地方。
SimpleExecutor
public abstract class BaseExecutor implements Executor {
protected abstract <E> List<E> doQuery(MappedStatement ms, Object parameter, RowBounds rowBounds, ResultHandler resultHandler, BoundSql boundSql)
throws SQLException;
}
public class SimpleExecutor extends BaseExecutor {
@Override
public <E> List<E> doQuery(MappedStatement ms, Object parameter, RowBounds rowBounds, ResultHandler resultHandler, BoundSql boundSql) throws SQLException {
Statement stmt = null;
try {
Configuration configuration = ms.getConfiguration();
// 创建 StatementHandler
StatementHandler handler = configuration.newStatementHandler(wrapper, ms, parameter, rowBounds, resultHandler, boundSql);
// 创建 Statement
stmt = prepareStatement(handler, ms.getStatementLog());
// 执行查询操作
return handler.<E>query(stmt, resultHandler);
} finally {
// 关闭 Statement
closeStatement(stmt);
}
}
}
上篇文章我们分析完了StatementHandler handler = configuration.newStatementHandler(wrapper, ms, parameter, rowBounds, resultHandler, boundSql)，在代码中创建了一个PreparedStatementHandler，我们要接着stmt = prepareStatement(handler, ms.getStatementLog())开始分析，也就是创建 Statement，先不忙着分析，我们先来回顾一下 ，我们以前是怎么使用jdbc的。
jdbc
public class JDBCDemo {
/**
* 第一步，加载驱动，创建数据库的连接
* 第二步，编写sql
* 第三步，需要对sql进行预编译
* 第四步，向sql里面设置参数
* 第五步，执行sql
* 第六步，释放资源
* @throws Exception
*/
public static final String URL = "jdbc:mysql://localhost:3306/demo";
public static final String USER = "root";
public static final String PASSWORD = "123456";
public static void main(String[] args) throws Exception {
jdbcDemo("lucy","123");
}
public static void jdbcDemo(String username , String password) throws Exception{
Connection conn = null;
PreparedStatement psmt = null;
ResultSet rs = null;
try {
//加载驱动程序
Class.forName("com.mysql.jdbc.Driver");
//获得数据库连接
conn = DriverManager.getConnection(URL, USER, PASSWORD);
//编写sql
String sql = "select * from user where name =? and password = ?";//问号相当于一个占位符
//对sql进行预编译
psmt = conn.prepareStatement(sql);
//设置参数
psmt.setString(1, username);
psmt.setString(2, password);
//执行sql ,返回一个结果集
rs = psmt.executeQuery();
//输出结果
while(rs.next()){
System.out.println(rs.getString("user_name")+" 年龄："+rs.getInt("age"));
}
} catch (Exception e) {
e.printStackTrace();
}finally{
//释放资源
conn.close();
psmt.close();
rs.close();
}
}
}
上面代码中注释已经很清楚了，我们来看看mybatis中是怎么和数据库打交道的。
SimpleExecutor
public class SimpleExecutor extends BaseExecutor {
private Statement prepareStatement(StatementHandler handler, Log statementLog) throws SQLException {
Statement stmt;
// 获取数据库连接
Connection connection = getConnection(statementLog);
// 创建 Statement
stmt = handler.prepare(connection, transaction.getTimeout());
// 为 Statement 设置参数
handler.parameterize(stmt);
return stmt;
}
}
在上面的代码中我们终于看到了和jdbc相关的内容了，大概分为下面三个步骤：
- 1、获取数据库连接。
- 2、创建PreparedStatement。
- 3、为PreparedStatement设置运行时参数。
我们先来看看获取数据库连接，跟进代码看看
BaseExecutor
public abstract class BaseExecutor implements Executor {
protected Transaction transaction;
protected Connection getConnection(Log statementLog) throws SQLException {
//通过transaction来获取Connection
Connection connection = transaction.getConnection();
if (statementLog.isDebugEnabled()) {
return ConnectionLogger.newInstance(connection, statementLog, queryStack);
} else {
return connection;
}
}
}
我们看到是通过Executor中的transaction属性来获取Connection，那我们就先来看看transaction，根据前面的文章中的配置 <transactionManager type="jdbc"/>，则MyBatis会创建一个JdbcTransactionFactory.class 实例，Executor中的transaction是一个JdbcTransaction.class 实例，其实现Transaction接口，那我们先来看看Transaction
JdbcTransaction
我们先来看看其接口Transaction
Transaction
public interface Transaction {
//获取数据库连接
Connection getConnection() throws SQLException;
//提交事务
void commit() throws SQLException;
//回滚事务
void rollback() throws SQLException;
//关闭事务
void close() throws SQLException;
//获取超时时间
Integer getTimeout() throws SQLException;
}
接着我们看看其实现类JdbcTransaction
JdbcTransaction
public class JdbcTransaction implements Transaction {
private static final Log log = LogFactory.getLog(JdbcTransaction.class);
//数据库连接
protected Connection connection;
//数据源信息
protected DataSource dataSource;
//隔离级别
protected TransactionIsolationLevel level;
//是否为自动提交
protected boolean autoCommmit;
public JdbcTransaction(DataSource ds, TransactionIsolationLevel desiredLevel, boolean desiredAutoCommit) {
dataSource = ds;
level = desiredLevel;
autoCommmit = desiredAutoCommit;
}
public JdbcTransaction(Connection connection) {
this.connection = connection;
}
@Override
public Connection getConnection() throws SQLException {
//如果事务中不存在connection，则获取一个connection并放入connection属性中
//第一次肯定为空
if (connection == null) {
openConnection();
}
//如果事务中已经存在connection，则直接返回这个connection
return connection;
}
/**
* commit()功能
* @throws SQLException
*/
@Override
public void commit() throws SQLException {
if (connection != null && !connection.getAutoCommit()) {
if (log.isDebugEnabled()) {
log.debug("Committing JDBC Connection [" + connection + "]");
}
//使用connection的commit()
connection.commit();
}
}
/**
* rollback()功能
* @throws SQLException
*/
@Override
public void rollback() throws SQLException {
if (connection != null && !connection.getAutoCommit()) {
if (log.isDebugEnabled()) {
log.debug("Rolling back JDBC Connection [" + connection + "]");
}
//使用connection的rollback()
connection.rollback();
}
}
/**
* close()功能
* @throws SQLException
*/
@Override
public void close() throws SQLException {
if (connection != null) {
resetAutoCommit();
if (log.isDebugEnabled()) {
log.debug("Closing JDBC Connection [" + connection + "]");
}
//使用connection的close()
connection.close();
}
}
protected void setDesiredAutoCommit(boolean desiredAutoCommit) {
try {
if (connection.getAutoCommit() != desiredAutoCommit) {
if (log.isDebugEnabled()) {
log.debug("Setting autocommit to " + desiredAutoCommit + " on JDBC Connection [" + connection + "]");
}
connection.setAutoCommit(desiredAutoCommit);
}
} catch (SQLException e) {
// Only a very poorly implemented driver would fail here,
// and there's not much we can do about that.
throw new TransactionException("Error configuring AutoCommit. "
+ "Your driver may not support getAutoCommit() or setAutoCommit(). "
+ "Requested setting: " + desiredAutoCommit + ". Cause: " + e, e);
}
}
protected void resetAutoCommit() {
try {
if (!connection.getAutoCommit()) {
// MyBatis does not call commit/rollback on a connection if just selects were performed.
// Some databases start transactions with select statements
// and they mandate a commit/rollback before closing the connection.
// A workaround is setting the autocommit to true before closing the connection.
// Sybase throws an exception here.
if (log.isDebugEnabled()) {
log.debug("Resetting autocommit to true on JDBC Connection [" + connection + "]");
}
//通过connection设置事务是否自动提交
connection.setAutoCommit(true);
}
} catch (SQLException e) {
if (log.isDebugEnabled()) {
log.debug("Error resetting autocommit to true "
+ "before closing the connection. Cause: " + e);
}
}
}
protected void openConnection() throws SQLException {
if (log.isDebugEnabled()) {
log.debug("Opening JDBC Connection");
}
//通过dataSource来获取connection，并设置到transaction的connection属性中
connection = dataSource.getConnection();
if (level != null) {
//通过connection设置事务的隔离级别
connection.setTransactionIsolation(level.getLevel());
}
//设置事务是否自动提交
setDesiredAutoCommit(autoCommmit);
}
@Override
public Integer getTimeout() throws SQLException {
return null;
}
}
我们看到JdbcTransaction中有一个Connection属性和dataSource属性，使用connection来进行提交、回滚、关闭等操作，也就是说JdbcTransaction其实只是在jdbc的connection上面封装了一下，实际使用的其实还是jdbc的事务。我们看看getConnection()方法
public class JdbcTransaction implements Transaction {
//数据库连接
protected Connection connection;
//数据源信息
protected DataSource dataSource;
@Override
public Connection getConnection() throws SQLException {
//如果事务中不存在connection，则获取一个connection并放入connection属性中
//第一次肯定为空
if (connection == null) {
openConnection();
}
//如果事务中已经存在connection，则直接返回这个connection
return connection;
}
protected void openConnection() throws SQLException {
if (log.isDebugEnabled()) {
log.debug("Opening JDBC Connection");
}
//通过dataSource来获取connection，并设置到transaction的connection属性中
connection = dataSource.getConnection();
if (level != null) {
//通过connection设置事务的隔离级别
connection.setTransactionIsolation(level.getLevel());
}
//设置事务是否自动提交
setDesiredAutoCommit(autoCommmit);
}
}
先是判断当前事务中是否存在connection，如果存在，则直接返回connection，如果不存在则通过dataSource来获取connection，这里我们明白了一点，如果当前事务没有关闭，也就是没有释放connection，那么在同一个Transaction中使用的是同一个connection，我们再来想想，transaction是SimpleExecutor中的属性，SimpleExecutor又是SqlSession中的属性，那我们可以这样说，同一个SqlSession中只有一个SimpleExecutor，SimpleExecutor中有一个Transaction，Transaction有一个connection。我们来看看如下例子
public static void main(String[] args) throws IOException {
String resource = "mybatis-config.xml";
InputStream inputStream = Resources.getResourceAsStream(resource);
SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
//创建一个SqlSession
SqlSession sqlSession = sqlSessionFactory.openSession();
try {
EmployeeMapper employeeMapper = sqlSession.getMapper(Employee.class);
UserMapper userMapper = sqlSession.getMapper(User.class);
List<Employee> allEmployee = employeeMapper.getAll();
List<User> allUser = userMapper.getAll();
Employee employee = employeeMapper.getOne();
} finally {
sqlSession.close();
}
}
我们看到同一个sqlSession可以获取多个Mapper代理对象，则多个Mapper代理对象中的sqlSession引用应该是同一个，那么多个Mapper代理对象调用方法应该是同一个Connection，直到调用close()，所以说我们的sqlSession是线程不安全的，如果所有的业务都使用一个sqlSession，那Connection也是同一个，一个业务执行完了就将其关闭，那其他的业务还没执行完呢。大家明白了吗？我们回归到源码，connection = dataSource.getConnection();，最终还是调用dataSource来获取连接，那我们是不是要来看看dataSource呢？
我们还是从前面的配置文件来看<dataSource type="UNPOOLED|POOLED">，这里有UNPOOLED和POOLED两种DataSource，一种是使用连接池，一种是普通的DataSource，UNPOOLED将会创将new UnpooledDataSource()实例，POOLED将会new pooledDataSource()实例，都实现DataSource接口，那我们先来看看DataSource接口
DataSource
public interface DataSource extends CommonDataSource, Wrapper {
//获取数据库连接
Connection getConnection() throws SQLException;
//获取数据库连接
Connection getConnection(String username, String password) throws SQLException;
}
很简单，只有一个获取数据库连接的接口，那我们来看看其实现类
UnpooledDataSource
UnpooledDataSource，从名称上即可知道，该种数据源不具有池化特性。该种数据源每次会返回一个新的数据库连接，而非复用旧的连接。其核心的方法有三个，分别如下：
- initializeDriver - 初始化数据库驱动
- doGetConnection - 获取数据连接
- configureConnection - 配置数据库连接
初始化数据库驱动
看下我们上面使用JDBC的例子，在执行 SQL 之前，通常都是先获取数据库连接。一般步骤都是加载数据库驱动，然后通过 DriverManager 获取数据库连接。UnpooledDataSource 也是使用 JDBC 访问数据库的，因此它获取数据库连接的过程一样。
UnpooledDataSource
public class UnpooledDataSource implements DataSource {
private ClassLoader driverClassLoader;
private Properties driverProperties;
private static Map<String, Driver> registeredDrivers = new ConcurrentHashMap<String, Driver>();
private String driver;
private String url;
private String username;
private String password;
private Boolean autoCommit;
private Integer defaultTransactionIsolationLevel;
static {
Enumeration<Driver> drivers = DriverManager.getDrivers();
while (drivers.hasMoreElements()) {
Driver driver = drivers.nextElement();
registeredDrivers.put(driver.getClass().getName(), driver);
}
}
public UnpooledDataSource() {
}
public UnpooledDataSource(String driver, String url, String username, String password) {
this.driver = driver;
this.url = url;
this.username = username;
this.password = password;
}
private synchronized void initializeDriver() throws SQLException {
// 检测当前 driver 对应的驱动实例是否已经注册
if (!registeredDrivers.containsKey(driver)) {
Class<?> driverType;
try {
// 加载驱动类型
if (driverClassLoader != null) {
// 使用 driverClassLoader 加载驱动
driverType = Class.forName(driver, true, driverClassLoader);
} else {
// 通过其他 ClassLoader 加载驱动
driverType = Resources.classForName(driver);
}
// DriverManager requires the driver to be loaded via the system ClassLoader.
// http://www.kfu.com/~nsayer/Java/dyn-jdbc.html
// 通过反射创建驱动实例
Driver driverInstance = (Driver)driverType.newInstance();
/*
* 注册驱动，注意这里是将 Driver 代理类 DriverProxy 对象注册到 DriverManager 中的，而非 Driver 对象本身。
*/
DriverManager.registerDriver(new DriverProxy(driverInstance));
// 缓存驱动类名和实例，防止多次注册
registeredDrivers.put(driver, driverInstance);
} catch (Exception e) {
throw new SQLException("Error setting driver on UnpooledDataSource. Cause: " + e);
}
}
}
//略......
}
public class DriverManager {
private final static CopyOnWriteArrayList<DriverInfo> registeredDrivers = new CopyOnWriteArrayList<>();
public static synchronized void registerDriver(java.sql.Driver driver)
throws SQLException {
registerDriver(driver, null);
}
public static synchronized void registerDriver(java.sql.Driver driver,
DriverAction da)
throws SQLException {
/* Register the driver if it has not already been added to our list */
if(driver != null) {
registeredDrivers.addIfAbsent(new DriverInfo(driver, da));
} else {
// This is for compatibility with the original DriverManager
throw new NullPointerException();
}
println("registerDriver: " + driver);
}
}
通过反射机制加载驱动Driver，并将其注册到DriverManager中的一个常量集合中，供后面获取连接时使用，为什么这里是一个List呢？我们实际开发中有可能使用到了多种数据库类型，如Mysql、Oracle等，其驱动都是不同的，不同的数据源获取连接时使用的是不同的驱动。
在我们使用JDBC的时候，也没有通过DriverManager.registerDriver(new DriverProxy(driverInstance));去注册Driver啊，如果我们使用的是Mysql数据源，那我们来看Class.forName("com.mysql.jdbc.Driver");这句代码发生了什么
Class.forName主要是做了什么呢？它主要是要求JVM查找并装载指定的类。这样我们的类com.mysql.jdbc.Driver就被装载进来了。而且在类被装载进JVM的时候，它的静态方法就会被执行。我们来看com.mysql.jdbc.Driver的实现代码。在它的实现里有这么一段代码：
static {
try {
java.sql.DriverManager.registerDriver(new Driver());
} catch (SQLException E) {
throw new RuntimeException("Can't register driver!");
}
}
很明显，这里使用了DriverManager并将该类给注册上去了。所以，对于任何实现前面Driver接口的类，只要在他们被装载进JVM的时候注册DriverManager就可以实现被后续程序使用。
作为那些被加载的Driver实现，他们本身在被装载时会在执行的static代码段里通过调用DriverManager.registerDriver()来把自身注册到DriverManager的registeredDrivers列表中。这样后面就可以通过得到的Driver来取得连接了。
获取数据库连接
在上面例子中使用 JDBC 时，我们都是通过 DriverManager 的接口方法获取数据库连接。我们来看看UnpooledDataSource是如何获取的。
UnpooledDataSource
public class UnpooledDataSource implements DataSource {
@Override
public Connection getConnection() throws SQLException {
return doGetConnection(username, password);
}
@Override
public Connection getConnection(String username, String password) throws SQLException {
return doGetConnection(username, password);
}
private Connection doGetConnection(String username, String password) throws SQLException {
Properties props = new Properties();
if (driverProperties != null) {
props.putAll(driverProperties);
}
if (username != null) {
// 存储 user 配置
props.setProperty("user", username);
}
if (password != null) {
// 存储 password 配置
props.setProperty("password", password);
}
// 调用重载方法
return doGetConnection(props);
}
private Connection doGetConnection(Properties properties) throws SQLException {
// 初始化驱动,我们上一节已经讲过了，只用初始化一次
initializeDriver();
// 获取连接
Connection connection = DriverManager.getConnection(url, properties);
// 配置连接，包括自动提交以及事务等级
configureConnection(connection);
return connection;
}
private void configureConnection(Connection conn) throws SQLException {
if (autoCommit != null && autoCommit != conn.getAutoCommit()) {
// 设置自动提交
conn.setAutoCommit(autoCommit);
}
if (defaultTransactionIsolationLevel != null) {
// 设置事务隔离级别
conn.setTransactionIsolation(defaultTransactionIsolationLevel);
}
}
}
上面方法将一些配置信息放入到 Properties 对象中，然后将数据库连接和 Properties 对象传给 DriverManager 的 getConnection 方法即可获取到数据库连接。我们来看看是怎么获取数据库连接的
public class DriverManager {
private final static CopyOnWriteArrayList<DriverInfo> registeredDrivers = new CopyOnWriteArrayList<>();
@CallerSensitive
public static Connection getConnection(String url,
java.util.Properties info) throws SQLException {
return (getConnection(url, info, Reflection.getCallerClass()));
}
private static Connection getConnection(
String url, java.util.Properties info, Class<?> caller) throws SQLException {
/*
* When callerCl is null, we should check the application's
* (which is invoking this class indirectly)
* classloader, so that the JDBC driver class outside rt.jar
* can be loaded from here.
*/
// 获取类加载器
ClassLoader callerCL = caller != null ? caller.getClassLoader() : null;
synchronized(DriverManager.class) {
// synchronize loading of the correct classloader.
if (callerCL == null) {
callerCL = Thread.currentThread().getContextClassLoader();
}
}
if(url == null) {
throw new SQLException("The url cannot be null", "08001");
}
println("DriverManager.getConnection(\"" + url + "\")");
// Walk through the loaded registeredDrivers attempting to make a connection.
// Remember the first exception that gets raised so we can reraise it.
SQLException reason = null;
// 此处省略部分代码
// 这里遍历的是在registerDriver(Driver driver)方法中注册的驱动对象
// 每个DriverInfo包含了驱动对象和其信息
for(DriverInfo aDriver : registeredDrivers) {
// If the caller does not have permission to load the driver then
// skip it.
// 判断是否为当前线程类加载器加载的驱动类
if(isDriverAllowed(aDriver.driver, callerCL)) {
try {
println(" trying " + aDriver.driver.getClass().getName());
// 获取连接对象，这里调用了Driver的父类的方法
// 如果这里有多个DriverInfo，比喻Mysql和Oracle的Driver都注册registeredDrivers了
// 这里所有的Driver都会尝试使用url和info去连接，哪个连接上了就返回
// 会不会所有的都会连接上呢？不会，因为url的写法不同，不同的Driver会判断url是否适合当前驱动
Connection con = aDriver.driver.connect(url, info);
if (con != null) {
// Success!
// 打印连接成功信息
println("getConnection returning " + aDriver.driver.getClass().getName());
// 返回连接对像
return (con);
}
} catch (SQLException ex) {
if (reason == null) {
reason = ex;
}
}
} else {
println(" skipping: " + aDriver.getClass().getName());
}
}
// if we got here nobody could connect.
if (reason != null) {
println("getConnection failed: " + reason);
throw reason;
}
println("getConnection: no suitable driver found for "+ url);
throw new SQLException("No suitable driver found for "+ url, "08001");
}
}
代码中循环所有注册的驱动，然后通过驱动进行连接，所有的驱动都会尝试连接，但是不同的驱动，连接的URL是不同的，Mysql的url是jdbc:mysql://localhost:3306/demo，以jdbc:mysql://开头，则其Mysql的驱动肯定会判断获取连接的url符合，Oracle的也类似。
由于篇幅原因，我这里就不分析了，大家有兴趣的可以看看，最后由URL对应的驱动获取到Connection返回，好了我们再来看看下一种DataSource
PooledDataSource
PooledDataSource 内部实现了连接池功能，用于复用数据库连接。因此，从效率上来说，PooledDataSource 要高于 UnpooledDataSource。但是最终获取Connection还是通过UnpooledDataSource，只不过PooledDataSource 提供一个存储Connection的功能。
辅助类介绍
PooledDataSource 需要借助两个辅助类帮其完成功能，这两个辅助类分别是 PoolState 和 PooledConnection。PoolState 用于记录连接池运行时的状态，比如连接获取次数，无效连接数量等。同时 PoolState 内部定义了两个 PooledConnection 集合，用于存储空闲连接和活跃连接。PooledConnection 内部定义了一个 Connection 类型的变量，用于指向真实的数据库连接。以及一个 Connection 的代理类，用于对部分方法调用进行拦截。至于为什么要拦截，随后将进行分析。除此之外，PooledConnection 内部也定义了一些字段，用于记录数据库连接的一些运行时状态。接下来，我们来看一下 PooledConnection 的定义。
class PooledConnection implements InvocationHandler {
private static final String CLOSE = "close";
private static final Class<?>[] IFACES = new Class<?>[] { Connection.class };
private final int hashCode;
private final PooledDataSource dataSource;
// 真实的数据库连接
private final Connection realConnection;
// 数据库连接代理
private final Connection proxyConnection;
// 从连接池中取出连接时的时间戳
private long checkoutTimestamp;
// 数据库连接创建时间
private long createdTimestamp;
// 数据库连接最后使用时间
private long lastUsedTimestamp;
// connectionTypeCode = (url + username + password).hashCode()
private int connectionTypeCode;
// 表示连接是否有效
private boolean valid;
public PooledConnection(Connection connection, PooledDataSource dataSource) {
this.hashCode = connection.hashCode();
this.realConnection = connection;
this.dataSource = dataSource;
this.createdTimestamp = System.currentTimeMillis();
this.lastUsedTimestamp = System.currentTimeMillis();
this.valid = true;
// 创建 Connection 的代理类对象
this.proxyConnection = (Connection) Proxy.newProxyInstance(Connection.class.getClassLoader(), IFACES, this);
}
// 省略部分代码......
}
下面再来看看 PoolState 的定义。
PoolState
public class PoolState {
protected PooledDataSource dataSource;
// 空闲连接列表
protected final List<PooledConnection> idleConnections = new ArrayList<PooledConnection>();
// 活跃连接列表
protected final List<PooledConnection> activeConnections = new ArrayList<PooledConnection>();
// 从连接池中获取连接的次数
protected long requestCount = 0;
// 请求连接总耗时（单位：毫秒）
protected long accumulatedRequestTime = 0;
// 连接执行时间总耗时
protected long accumulatedCheckoutTime = 0;
// 执行时间超时的连接数
protected long claimedOverdueConnectionCount = 0;
// 超时时间累加值
protected long accumulatedCheckoutTimeOfOverdueConnections = 0;
// 等待时间累加值
protected long accumulatedWaitTime = 0;
// 等待次数
protected long hadToWaitCount = 0;
// 无效连接数
protected long badConnectionCount = 0;
// 省略部分代码......
}
大家记住上面的空闲连接列表和活跃连接列表
获取连接
前面已经说过，PooledDataSource 会将用过的连接进行回收，以便可以复用连接。因此从 PooledDataSource 获取连接时，如果空闲链接列表里有连接时，可直接取用。那如果没有空闲连接怎么办呢？此时有两种解决办法，要么创建新连接，要么等待其他连接完成任务。
PooledDataSource
public class PooledDataSource implements DataSource {
private static final Log log = LogFactory.getLog(PooledDataSource.class);
private final PoolState state = new PoolState(this);
private final UnpooledDataSource dataSource;
// OPTIONAL CONFIGURATION FIELDS
protected int poolMaximumActiveConnections = 10;
protected int poolMaximumIdleConnections = 5;
protected int poolMaximumCheckoutTime = 20000;
protected int poolTimeToWait = 20000;
protected int poolMaximumLocalBadConnectionTolerance = 3;
protected String poolPingQuery = "NO PING QUERY SET";
protected boolean poolPingEnabled;
protected int poolPingConnectionsNotUsedFor;
private int expectedConnectionTypeCode;
public PooledDataSource() {
//构造器中创建UnpooledDataSource对象
dataSource = new UnpooledDataSource();
}
public PooledDataSource(UnpooledDataSource dataSource) {
this.dataSource = dataSource;
}
@Override
public Connection getConnection() throws SQLException {
return popConnection(dataSource.getUsername(), dataSource.getPassword()).getProxyConnection();
}
private PooledConnection popConnection(String username, String password) throws SQLException {
boolean countedWait = false;
PooledConnection conn = null;
long t = System.currentTimeMillis();
int localBadConnectionCount = 0;
while (conn == null) {
synchronized (state) {
// 检测空闲连接集合（idleConnections）是否为空
if (!state.idleConnections.isEmpty()) {
// Pool has available connection
// idleConnections 不为空，表示有空闲连接可以使用，直接从空闲连接集合中取出一个连接
conn = state.idleConnections.remove(0);
if (log.isDebugEnabled()) {
log.debug("Checked out connection " + conn.getRealHashCode() + " from pool.");
}
} else {
// Pool does not have available connection
/*
* 暂无空闲连接可用，但如果活跃连接数还未超出限制
*（poolMaximumActiveConnections），则可创建新的连接
*/
if (state.activeConnections.size() < poolMaximumActiveConnections) {
// Can create new connection
// 创建新连接，看到没，还是通过dataSource获取连接，也就是UnpooledDataSource获取连接
conn = new PooledConnection(dataSource.getConnection(), this);
if (log.isDebugEnabled()) {
log.debug("Created connection " + conn.getRealHashCode() + ".");
}
} else {
// Cannot create new connection
// 连接池已满，不能创建新连接
// 取出运行时间最长的连接
PooledConnection oldestActiveConnection = state.activeConnections.get(0);
// 获取运行时长
long longestCheckoutTime = oldestActiveConnection.getCheckoutTime();
// 检测运行时长是否超出限制，即超时
if (longestCheckoutTime > poolMaximumCheckoutTime) {
// Can claim overdue connection
// 累加超时相关的统计字段
state.claimedOverdueConnectionCount++;
state.accumulatedCheckoutTimeOfOverdueConnections += longestCheckoutTime;
state.accumulatedCheckoutTime += longestCheckoutTime;
// 从活跃连接集合中移除超时连接
state.activeConnections.remove(oldestActiveConnection);
// 若连接未设置自动提交，此处进行回滚操作
if (!oldestActiveConnection.getRealConnection().getAutoCommit()) {
try {
oldestActiveConnection.getRealConnection().rollback();
} catch (SQLException e) {
log.debug("Bad connection. Could not roll back");
}
}
/*
* 创建一个新的 PooledConnection，注意，
* 此处复用 oldestActiveConnection 的 realConnection 变量
*/
conn = new PooledConnection(oldestActiveConnection.getRealConnection(), this);
/*
* 复用 oldestActiveConnection 的一些信息，注意 PooledConnection 中的
* createdTimestamp 用于记录 Connection 的创建时间，而非 PooledConnection
* 的创建时间。所以这里要复用原连接的时间信息。
*/
conn.setCreatedTimestamp(oldestActiveConnection.getCreatedTimestamp());
conn.setLastUsedTimestamp(oldestActiveConnection.getLastUsedTimestamp());
// 设置连接为无效状态
oldestActiveConnection.invalidate();
if (log.isDebugEnabled()) {
log.debug("Claimed overdue connection " + conn.getRealHashCode() + ".");
}
} else {
// Must wait
// 运行时间最长的连接并未超时
try {
if (!countedWait) {
state.hadToWaitCount++;
countedWait = true;
}
if (log.isDebugEnabled()) {
log.debug("Waiting as long as " + poolTimeToWait + " milliseconds for connection.");
}
long wt = System.currentTimeMillis();
// 当前线程进入等待状态
state.wait(poolTimeToWait);
state.accumulatedWaitTime += System.currentTimeMillis() - wt;
} catch (InterruptedException e) {
break;
}
}
}
}
if (conn != null) {
// ping to server and check the connection is valid or not
if (conn.isValid()) {
if (!conn.getRealConnection().getAutoCommit()) {
// 进行回滚操作
conn.getRealConnection().rollback();
}
// 设置统计字段
conn.setConnectionTypeCode(assembleConnectionTypeCode(dataSource.getUrl(), username, password));
conn.setCheckoutTimestamp(System.currentTimeMillis());
conn.setLastUsedTimestamp(System.currentTimeMillis());
state.activeConnections.add(conn);
state.requestCount++;
state.accumulatedRequestTime += System.currentTimeMillis() - t;
} else {
if (log.isDebugEnabled()) {
log.debug("A bad connection (" + conn.getRealHashCode() + ") was returned from the pool, getting another connection.");
}
// 连接无效，此时累加无效连接相关的统计字段
state.badConnectionCount++;
localBadConnectionCount++;
conn = null;
if (localBadConnectionCount > (poolMaximumIdleConnections + poolMaximumLocalBadConnectionTolerance)) {
if (log.isDebugEnabled()) {
log.debug("PooledDataSource: Could not get a good connection to the database.");
}
throw new SQLException("PooledDataSource: Could not get a good connection to the database.");
}
}
}
}
}
if (conn == null) {
if (log.isDebugEnabled()) {
log.debug("PooledDataSource: Unknown severe error condition. The connection pool returned a null connection.");
}
throw new SQLException("PooledDataSource: Unknown severe error condition. The connection pool returned a null connection.");
}
return conn;
}
}
从连接池中获取连接首先会遇到两种情况：
- 1、连接池中有空闲连接。
- 2、连接池中无空闲连接。
对于第一种情况，把连接取出返回即可。对于第二种情况，则要进行细分，会有如下的情况。
- 1、活跃连接数没有超出最大活跃连接数。
- 2、活跃连接数超出最大活跃连接数。
对于上面两种情况，第一种情况比较好处理，直接创建新的连接即可。至于第二种情况，需要再次进行细分。
- 1、活跃连接的运行时间超出限制，即超时了
- 2、活跃连接未超时
对于第一种情况，我们直接将超时连接强行中断，并进行回滚，然后复用部分字段重新创建 PooledConnection 即可。对于第二种情况，目前没有更好的处理方式了，只能等待了。
回收连接
相比于获取连接，回收连接的逻辑要简单的多。回收连接成功与否只取决于空闲连接集合的状态，所需处理情况很少，因此比较简单。
我们还是来看看
public class PooledDataSource implements DataSource {
@Override
public Connection getConnection() throws SQLException {
return popConnection(dataSource.getUsername(), dataSource.getPassword()).getProxyConnection();
}
}
返回的是PooledConnection的一个代理类，为什么不直接使用PooledConnection的realConnection呢？我们可以看下PooledConnection这个类
class PooledConnection implements InvocationHandler
很熟悉是吧，标准的代理类用法，看下其invoke方法
PooledConnection
class PooledConnection implements InvocationHandler {
private final PooledDataSource dataSource;
private final Connection realConnection;
private final Connection proxyConnection;
@Override
public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
String methodName = method.getName();
// 重点在这里，如果调用了其close方法，则实际执行的是将连接放回连接池的操作
if (CLOSE.hashCode() == methodName.hashCode() && CLOSE.equals(methodName)) {
dataSource.pushConnection(this);
return null;
} else {
try {
if (!Object.class.equals(method.getDeclaringClass())) {
// issue #579 toString() should never fail
// throw an SQLException instead of a Runtime
checkConnection();
}
// 其他的操作都交给realConnection执行
return method.invoke(realConnection, args);
} catch (Throwable t) {
throw ExceptionUtil.unwrapThrowable(t);
}
}
}
}
那我们来看看pushConnection做了什么
public class PooledDataSource implements DataSource {
private final PoolState state = new PoolState(this);
protected void pushConnection(PooledConnection conn) throws SQLException {
synchronized (state) {
// 从活跃连接池中移除连接
state.activeConnections.remove(conn);
if (conn.isValid()) {
// 空闲连接集合未满
if (state.idleConnections.size() < poolMaximumIdleConnections && conn.getConnectionTypeCode() == expectedConnectionTypeCode) {
state.accumulatedCheckoutTime += conn.getCheckoutTime();
// 回滚未提交的事务
if (!conn.getRealConnection().getAutoCommit()) {
conn.getRealConnection().rollback();
}
// 创建新的 PooledConnection
PooledConnection newConn = new PooledConnection(conn.getRealConnection(), this);
state.idleConnections.add(newConn);
// 复用时间信息
newConn.setCreatedTimestamp(conn.getCreatedTimestamp());
newConn.setLastUsedTimestamp(conn.getLastUsedTimestamp());
// 将原连接置为无效状态
conn.invalidate();
if (log.isDebugEnabled()) {
log.debug("Returned connection " + newConn.getRealHashCode() + " to pool.");
}
// 通知等待的线程
state.notifyAll();
} else {
// 空闲连接集合已满
state.accumulatedCheckoutTime += conn.getCheckoutTime();
// 回滚未提交的事务
if (!conn.getRealConnection().getAutoCommit()) {
conn.getRealConnection().rollback();
}
// 关闭数据库连接
conn.getRealConnection().close();
if (log.isDebugEnabled()) {
log.debug("Closed connection " + conn.getRealHashCode() + ".");
}
conn.invalidate();
}
} else {
if (log.isDebugEnabled()) {
log.debug("A bad connection (" + conn.getRealHashCode() + ") attempted to return to the pool, discarding connection.");
}
state.badConnectionCount++;
}
}
}
}
先将连接从活跃连接集合中移除，如果空闲集合未满，此时复用原连接的字段信息创建新的连接，并将其放入空闲集合中即可；若空闲集合已满，此时无需回收连接，直接关闭即可。
连接池总觉得很神秘，但仔细分析完其代码之后，也就没那么神秘了，就是将连接使用完之后放到一个集合中，下面再获取连接的时候首先从这个集合中获取。 还有PooledConnection的代理模式的使用，值得我们学习
好了，我们已经获取到了数据库连接，接下来要创建PrepareStatement了，我们上面JDBC的例子是怎么获取的？ psmt = conn.prepareStatement(sql);，直接通过Connection来获取，并且把sql传进去了，我们看看Mybaits中是怎么创建PrepareStatement的
创建PreparedStatement
BaseStatementHandler
stmt = handler.prepare(connection, transaction.getTimeout());
public abstract class BaseStatementHandler implements StatementHandler {
protected BoundSql boundSql;
@Override
public Statement prepare(Connection connection, Integer transactionTimeout) throws SQLException {
ErrorContext.instance().sql(boundSql.getSql());
Statement statement = null;
try {
// 创建 Statement
statement = instantiateStatement(connection);
// 设置超时和 FetchSize
setStatementTimeout(statement, transactionTimeout);
setFetchSize(statement);
return statement;
} catch (SQLException e) {
closeStatement(statement);
throw e;
} catch (Exception e) {
closeStatement(statement);
throw new ExecutorException("Error preparing statement. Cause: " + e, e);
}
}
protected abstract Statement instantiateStatement(Connection connection) throws SQLException;
}
public class PreparedStatementHandler extends BaseStatementHandler {
@Override
protected Statement instantiateStatement(Connection connection) throws SQLException {
//获取sql字符串，比如"select * from user where id= ?"
String sql = boundSql.getSql();
// 根据条件调用不同的 prepareStatement 方法创建 PreparedStatement
if (mappedStatement.getKeyGenerator() instanceof Jdbc3KeyGenerator) {
String[] keyColumnNames = mappedStatement.getKeyColumns();
if (keyColumnNames == null) {
//通过connection获取Statement，将sql语句传进去
return connection.prepareStatement(sql, PreparedStatement.RETURN_GENERATED_KEYS);
} else {
return connection.prepareStatement(sql, keyColumnNames);
}
} else if (mappedStatement.getResultSetType() != null) {
return connection.prepareStatement(sql, mappedStatement.getResultSetType().getValue(), ResultSet.CONCUR_READ_ONLY);
} else {
return connection.prepareStatement(sql);
}
}
}
看到没和jdbc的形式一模一样，我们具体来看看connection.prepareStatement做了什么
public class ConnectionImpl implements JdbcConnection, SessionEventListener, Serializable {
public PreparedStatement prepareStatement(String sql, int resultSetType, int resultSetConcurrency) throws SQLException {
try {
synchronized(this.getConnectionMutex()) {
this.checkClosed();
ClientPreparedStatement pStmt = null;
boolean canServerPrepare = true;
String nativeSql = (Boolean)this.processEscapeCodesForPrepStmts.getValue() ? this.nativeSQL(sql) : sql;
if ((Boolean)this.useServerPrepStmts.getValue() && (Boolean)this.emulateUnsupportedPstmts.getValue()) {
canServerPrepare = this.canHandleAsServerPreparedStatement(nativeSql);
}
if ((Boolean)this.useServerPrepStmts.getValue() && canServerPrepare) {
if ((Boolean)this.cachePrepStmts.getValue()) {
synchronized(this.serverSideStatementCache) {
pStmt = (ClientPreparedStatement)this.serverSideStatementCache.remove(new ConnectionImpl.CompoundCacheKey(this.database, sql));
if (pStmt != null) {
((ServerPreparedStatement)pStmt).setClosed(false);
((ClientPreparedStatement)pStmt).clearParameters();
}
if (pStmt == null) {
try {
//这里使用的是ServerPreparedStatement创建PreparedStatement
pStmt = ServerPreparedStatement.getInstance(this.getMultiHostSafeProxy(), nativeSql, this.database, resultSetType, resultSetConcurrency);
if (sql.length() < (Integer)this.prepStmtCacheSqlLimit.getValue()) {
((ServerPreparedStatement)pStmt).isCacheable = true;
}
((ClientPreparedStatement)pStmt).setResultSetType(resultSetType);
((ClientPreparedStatement)pStmt).setResultSetConcurrency(resultSetConcurrency);
} catch (SQLException var14) {
if (!(Boolean)this.emulateUnsupportedPstmts.getValue()) {
throw var14;
}
pStmt = (ClientPreparedStatement)this.clientPrepareStatement(nativeSql, resultSetType, resultSetConcurrency, false);
if (sql.length() < (Integer)this.prepStmtCacheSqlLimit.getValue()) {
this.serverSideStatementCheckCache.put(sql, Boolean.FALSE);
}
}
}
}
} else {
try {
pStmt = ServerPreparedStatement.getInstance(this.getMultiHostSafeProxy(), nativeSql, this.database, resultSetType, resultSetConcurrency);
((ClientPreparedStatement)pStmt).setResultSetType(resultSetType);
((ClientPreparedStatement)pStmt).setResultSetConcurrency(resultSetConcurrency);
} catch (SQLException var13) {
if (!(Boolean)this.emulateUnsupportedPstmts.getValue()) {
throw var13;
}
pStmt = (ClientPreparedStatement)this.clientPrepareStatement(nativeSql, resultSetType, resultSetConcurrency, false);
}
}
} else {
pStmt = (ClientPreparedStatement)this.clientPrepareStatement(nativeSql, resultSetType, resultSetConcurrency, false);
}
return (PreparedStatement)pStmt;
}
} catch (CJException var17) {
throw SQLExceptionsMapping.translateException(var17, this.getExceptionInterceptor());
}
}
}
我们只用看最关键的代码，使用ServerPreparedStatement的getInstance返回一个PreparedStatement，其实本质上ServerPreparedStatement继承了PreparedStatement对象，我们看看其构造方法
public class ServerPreparedStatement extends ClientPreparedStatement {
protected static ServerPreparedStatement getInstance(JdbcConnection conn, String sql, String db, int resultSetType, int resultSetConcurrency) throws SQLException {
return new ServerPreparedStatement(conn, sql, db, resultSetType, resultSetConcurrency);
}
protected ServerPreparedStatement(JdbcConnection conn, String sql, String db, int resultSetType, int resultSetConcurrency) throws SQLException {
super(conn, db);
this.checkNullOrEmptyQuery(sql);
String statementComment = this.session.getProtocol().getQueryComment();
((PreparedQuery)this.query).setOriginalSql(statementComment == null ? sql : "/* " + statementComment + " */ " + sql);
((PreparedQuery)this.query).setParseInfo(new ParseInfo(((PreparedQuery)this.query).getOriginalSql(), this.session, this.charEncoding));
this.hasOnDuplicateKeyUpdate = ((PreparedQuery)this.query).getParseInfo().getFirstStmtChar() == 'I' && this.containsOnDuplicateKeyInString(sql);
try {
this.serverPrepare(sql);
} catch (SQLException | CJException var8) {
this.realClose(false, true);
throw SQLExceptionsMapping.translateException(var8, this.exceptionInterceptor);
}
this.setResultSetType(resultSetType);
this.setResultSetConcurrency(resultSetConcurrency);
}
}
设置运行时参数到 SQL 中
我们已经获取到了PreparedStatement，接下来就是将运行时参数设置到PreparedStatement中，如下代码
handler.parameterize(stmt);
我们来看看parameterize方法
public class PreparedStatementHandler extends BaseStatementHandler {
@Override
public void parameterize(Statement statement) throws SQLException {
// 通过参数处理器 ParameterHandler 设置运行时参数到 PreparedStatement 中
parameterHandler.setParameters((PreparedStatement) statement);
}
}
public interface ParameterHandler {
void setParameters(PreparedStatement ps)
throws SQLException;
}
public class DefaultParameterHandler implements ParameterHandler {
private final TypeHandlerRegistry typeHandlerRegistry;
private final MappedStatement mappedStatement;
private final Object parameterObject;
private final BoundSql boundSql;
private final Configuration configuration;
@Override
public void setParameters(PreparedStatement ps) {
ErrorContext.instance().activity("setting parameters").object(mappedStatement.getParameterMap().getId());
/*
* 从 BoundSql 中获取 ParameterMapping 列表，每个 ParameterMapping 与原始 SQL 中的 #{xxx} 占位符一一对应
*/
List<ParameterMapping> parameterMappings = boundSql.getParameterMappings();
if (parameterMappings != null) {
for (int i = 0; i < parameterMappings.size(); i++) {
ParameterMapping parameterMapping = parameterMappings.get(i);
if (parameterMapping.getMode() != ParameterMode.OUT) {
Object value;
// 获取属性名
String propertyName = parameterMapping.getProperty();
if (boundSql.hasAdditionalParameter(propertyName)) { // issue #448 ask first for additional params
value = boundSql.getAdditionalParameter(propertyName);
} else if (parameterObject == null) {
value = null;
} else if (typeHandlerRegistry.hasTypeHandler(parameterObject.getClass())) {
value = parameterObject;
} else {
// 为用户传入的参数 parameterObject 创建元信息对象
MetaObject metaObject = configuration.newMetaObject(parameterObject);
// 从用户传入的参数中获取 propertyName 对应的值
value = metaObject.getValue(propertyName);
}
TypeHandler typeHandler = parameterMapping.getTypeHandler();
JdbcType jdbcType = parameterMapping.getJdbcType();
if (value == null && jdbcType == null) {
jdbcType = configuration.getJdbcTypeForNull();
}
try {
// 由类型处理器 typeHandler 向 ParameterHandler 设置参数
typeHandler.setParameter(ps, i + 1, value, jdbcType);
} catch (TypeException e) {
throw new TypeException("Could not set parameters for mapping: " + parameterMapping + ". Cause: " + e, e);
} catch (SQLException e) {
throw new TypeException("Could not set parameters for mapping: " + parameterMapping + ". Cause: " + e, e);
}
}
}
}
}
}
首先从boundSql中获取parameterMappings 集合，这块大家可以看看我前面的文章，然后遍历获取 parameterMapping中的propertyName ，如#{name} 中的name,然后从运行时参数parameterObject中获取name对应的参数值，最后设置到PreparedStatement 中，我们主要来看是如何设置参数的。也就是typeHandler.setParameter(ps, i + 1, value, jdbcType);，这句代码最终会向我们例子中一样执行，如下
public class StringTypeHandler extends BaseTypeHandler<String> {
@Override
public void setNonNullParameter(PreparedStatement ps, int i, String parameter, JdbcType jdbcType)
throws SQLException {
ps.setString(i, parameter);
}
}
还记得我们的PreparedStatement是什么吗？是ServerPreparedStatement，那我们就来看看ServerPreparedStatement的setString方法
public class ServerPreparedStatement extends ClientPreparedStatement {
@Override
public void setURL(int parameterIndex, URL x) throws SQLException {
checkClosed();
setString(parameterIndex, x.toString());
}
}
public class ClientPreparedStatement extends com.mysql.cj.jdbc.StatementImpl implements JdbcPreparedStatement {
@Override
public void setString(int parameterIndex, String x) throws SQLException {
synchronized (checkClosed().getConnectionMutex()) {
((PreparedQuery<?>) this.query).getQueryBindings().setString(getCoreParameterIndex(parameterIndex), x);
}
}
}
public class ServerPreparedQueryBindings extends AbstractQueryBindings<ServerPreparedQueryBindValue> {
@Override
public void setString(int parameterIndex, String x) {
if (x == null) {
setNull(parameterIndex);
} else {
//根据参数下标从parameterBindings数组总获取BindValue
ServerPreparedQueryBindValue binding = getBinding(parameterIndex, false);
this.sendTypesToServer.compareAndSet(false, binding.resetToType(MysqlType.FIELD_TYPE_VAR_STRING, this.numberOfExecutions));
//设置参数值
binding.value = x;
binding.charEncoding = this.charEncoding;
binding.parameterType = MysqlType.VARCHAR;
}
}
}
public class ServerPreparedQueryBindings extends AbstractQueryBindings<ServerPreparedQueryBindValue> {
public ServerPreparedQueryBindValue getBinding(int parameterIndex, boolean forLongData) {
if (this.bindValues[parameterIndex] == null) {
// this.bindValues[parameterIndex] = new ServerPreparedQueryBindValue();
} else {
if (this.bindValues[parameterIndex].isStream && !forLongData) {
this.longParameterSwitchDetected = true;
}
}
//根据参数下标从bindValues数组中获取BindValue
return this.bindValues[parameterIndex];
}
}
执行查询
执行查询操作就是我们文章开头的最后一行代码，如下
return handler.<E>query(stmt, resultHandler);
我们来看看query是怎么做的
public class PreparedStatementHandler extends BaseStatementHandler {
@Override
public <E> List<E> query(Statement statement, ResultHandler resultHandler) throws SQLException {
PreparedStatement ps = (PreparedStatement) statement;
//直接执行ServerPreparedStatement的execute方法
ps.execute();
return resultSetHandler.<E> handleResultSets(ps);
}
}
public class ClientPreparedStatement extends com.mysql.cj.jdbc.StatementImpl implements JdbcPreparedStatement {
@Override
public boolean execute() throws SQLException {
synchronized (checkClosed().getConnectionMutex()) {
JdbcConnection locallyScopedConn = this.connection;
if (!this.doPingInstead && !checkReadOnlySafeStatement()) {
throw SQLError.createSQLException(Messages.getString("PreparedStatement.20") + Messages.getString("PreparedStatement.21"),
MysqlErrorNumbers.SQL_STATE_ILLEGAL_ARGUMENT, this.exceptionInterceptor);
}
ResultSetInternalMethods rs = null;
this.lastQueryIsOnDupKeyUpdate = false;
if (this.retrieveGeneratedKeys) {
this.lastQueryIsOnDupKeyUpdate = containsOnDuplicateKeyUpdateInSQL();
}
this.batchedGeneratedKeys = null;
resetCancelledState();
implicitlyCloseAllOpenResults();
clearWarnings();
if (this.doPingInstead) {
doPingInstead();
return true;
}
setupStreamingTimeout(locallyScopedConn);
Message sendPacket = ((PreparedQuery<?>) this.query).fillSendPacket();
String oldDb = null;
if (!locallyScopedConn.getDatabase().equals(this.getCurrentDatabase())) {
oldDb = locallyScopedConn.getDatabase();
locallyScopedConn.setDatabase(this.getCurrentDatabase());
}
//
// Check if we have cached metadata for this query...
//
CachedResultSetMetaData cachedMetadata = null;
boolean cacheResultSetMetadata = locallyScopedConn.getPropertySet().getBooleanProperty(PropertyKey.cacheResultSetMetadata).getValue();
if (cacheResultSetMetadata) {
cachedMetadata = locallyScopedConn.getCachedMetaData(((PreparedQuery<?>) this.query).getOriginalSql());
}
//
// Only apply max_rows to selects
//
locallyScopedConn.setSessionMaxRows(((PreparedQuery<?>) this.query).getParseInfo().getFirstStmtChar() == 'S' ? this.maxRows : -1);
rs = executeInternal(this.maxRows, sendPacket, createStreamingResultSet(),
(((PreparedQuery<?>) this.query).getParseInfo().getFirstStmtChar() == 'S'), cachedMetadata, false);
if (cachedMetadata != null) {
locallyScopedConn.initializeResultsMetadataFromCache(((PreparedQuery<?>) this.query).getOriginalSql(), cachedMetadata, rs);
} else {
if (rs.hasRows() && cacheResultSetMetadata) {
locallyScopedConn.initializeResultsMetadataFromCache(((PreparedQuery<?>) this.query).getOriginalSql(), null /* will be created */, rs);
}
}
if (this.retrieveGeneratedKeys) {
rs.setFirstCharOfQuery(((PreparedQuery<?>) this.query).getParseInfo().getFirstStmtChar());
}
if (oldDb != null) {
locallyScopedConn.setDatabase(oldDb);
}
if (rs != null) {
this.lastInsertId = rs.getUpdateID();
this.results = rs;
}
return ((rs != null) && rs.hasRows());
}
}
}
只看最关键的executeInternal方法
public class ClientPreparedStatement extends com.mysql.cj.jdbc.StatementImpl implements JdbcPreparedStatement {
protected <M extends Message> ResultSetInternalMethods executeInternal(int maxRowsToRetrieve, M sendPacket, boolean createStreamingResultSet,
boolean queryIsSelectOnly, ColumnDefinition metadata, boolean isBatch) throws SQLException {
synchronized (checkClosed().getConnectionMutex()) {
try {
JdbcConnection locallyScopedConnection = this.connection;
((PreparedQuery<?>) this.query).getQueryBindings()
.setNumberOfExecutions(((PreparedQuery<?>) this.query).getQueryBindings().getNumberOfExecutions() + 1);
ResultSetInternalMethods rs;
CancelQueryTask timeoutTask = null;
try {
timeoutTask = startQueryTimer(this, getTimeoutInMillis());
if (!isBatch) {
statementBegins();
}
//执行sql并返回结果
rs = ((NativeSession) locallyScopedConnection.getSession()).execSQL(this, null, maxRowsToRetrieve, (NativePacketPayload) sendPacket,
createStreamingResultSet, getResultSetFactory(), metadata, isBatch);
if (timeoutTask != null) {
stopQueryTimer(timeoutTask, true, true);
timeoutTask = null;
}
} finally {
if (!isBatch) {
this.query.getStatementExecuting().set(false);
}
stopQueryTimer(timeoutTask, false, false);
}
return rs;
} catch (NullPointerException npe) {
checkClosed(); // we can't synchronize ourselves against async connection-close due to deadlock issues, so this is the next best thing for
// this particular corner case.
throw npe;
}
}
}
}
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