com.mysql.cj.jdbc.Driver 解析

Driver类的文档描述:

package com.mysql.cj.jdbc;

import java.sql.SQLException;

/**
 * The Java SQL framework allows for multiple database drivers. Each driver should supply a class that implements the Driver interface
 * 
 * <p>
 * The DriverManager will try to load as many drivers as it can find and then for any given connection request, it will ask each driver in turn to try to
 * connect to the target URL.
 * 
 * <p>
 * It is strongly recommended that each Driver class should be small and standalone so that the Driver class can be loaded and queried without bringing in vast
 * quantities of supporting code.
 * 
 * <p>
 * When a Driver class is loaded, it should create an instance of itself and register it with the DriverManager. This means that a user can load and register a
 * driver by doing Class.forName("foo.bah.Driver")
 */
public class Driver extends NonRegisteringDriver implements java.sql.Driver {
    //
    // Register ourselves with the DriverManager
    //
    static {
        try {
            java.sql.DriverManager.registerDriver(new Driver());
        } catch (SQLException E) {
            throw new RuntimeException("Can't register driver!");
        }
    }

    /**
     * Construct a new driver and register it with DriverManager
     * 
     * @throws SQLException
     *             if a database error occurs.
     */
    public Driver() throws SQLException {
        // Required for Class.forName().newInstance()
    }
}

这里的英文描述核心是说:

1.Driver类要保证自己被加载时就主动注册到DriverManager里

2.DriverManager会一次尝试使用每个Driver与数据库建立连接

3.每个Driver实现类需要实现java.sql.Driver接口

4.Driver实现类不应该有依赖项,自己作为一个jar包就可以完成工作;

对于描述1,可以看到Driver的static代码块中调用了

java.sql.DriverManager.registerDriver(new Driver())

来保证Class被加载时就能注册进DriverManager里,这行代码是怎么执行注册的呢?,跟踪发现调用链:

java.sql.DriverManager.registerDriver

->registerDriver(java.sql.Driver driver,DriverAction da /*注册时该变量为Null,该类的负责取消注册*/)

->registeredDrivers.addIfAbsent(new DriverInfo(driver, da));

registerDrivers的定义如下,所以注册就是加入DriverManager的属性队列里

 private final static CopyOnWriteArrayList<DriverInfo> registeredDrivers = new CopyOnWriteArrayList<>();

com.mysql.cj.jdbc.Driver类通过继承NonRegisteringDriver来实现java.sql.Driver里的方法.NonRegisteringDriver类

NonRegisteringDriver 的静态代码块会开启一个清理mysql弃置连接的后台线程,核心是通过软引用实现的.

    static {
        try {
            Class.forName(AbandonedConnectionCleanupThread.class.getName());
        } catch (ClassNotFoundException e) {
            // ignore
        }
    }


Reference<? extends MysqlConnection> reference是一个软引用队列,jvm进行垃圾回收时,完成对垃圾回收对象的回收后会把被回收的对象放到这个队列里,AbandonedConnectionCleanupThread对象拿到后调用方法finalizeResource方法关闭MysqlConnection的底层连接以及InputStream和OutputStream
AbandonedConnectionCleanupThread
public void run() {
        for (;;) {
            try {
                checkThreadContextClassLoader();
                Reference<? extends MysqlConnection> reference = referenceQueue.remove(5000);
                if (reference != null) {
                    finalizeResource((ConnectionFinalizerPhantomReference) reference);
                }
            } catch (InterruptedException e) {
                threadRefLock.lock();
                try {
                    threadRef = null;

                    // Finalize remaining references.
                    Reference<? extends MysqlConnection> reference;
                    while ((reference = referenceQueue.poll()) != null) {
                        finalizeResource((ConnectionFinalizerPhantomReference) reference);
                    }
                    connectionFinalizerPhantomRefs.clear();
                } finally {
                    threadRefLock.unlock();
                }
                return;
            } catch (Exception ex) {
                // Nowhere to really log this.
            }
        }
    }

ConnectionImpl

ConnectionImpl类完成参数设置,交给NativerSocketConnection完成底层连接,构造函数里的createNewIO方法完成连接

HostInfo类保存连接的信息,比如host,port,username,password, hostProperties

NativeSocketConnection

NativeSocketConnection 的connection方法完成建立连接以及读写缓冲区分配,读写缓冲区大小居为16M,

    @Override
    public void connect(String hostName, int portNumber, PropertySet propSet, ExceptionInterceptor excInterceptor, Log log, int loginTimeout) {

        try {
            this.port = portNumber;
            this.host = hostName;
            this.propertySet = propSet;
            this.exceptionInterceptor = excInterceptor;

            this.socketFactory = createSocketFactory(propSet.getStringProperty(PropertyKey.socketFactory).getStringValue());
            this.mysqlSocket = this.socketFactory.connect(this.host, this.port, propSet, loginTimeout);

            int socketTimeout = propSet.getIntegerProperty(PropertyKey.socketTimeout).getValue();
            if (socketTimeout != 0) {
                try {
                    this.mysqlSocket.setSoTimeout(socketTimeout);
                } catch (Exception ex) {
                    /* Ignore if the platform does not support it */
                }
            }

            this.socketFactory.beforeHandshake();

            InputStream rawInputStream;
            if (propSet.getBooleanProperty(PropertyKey.useReadAheadInput).getValue()) {
                rawInputStream = new ReadAheadInputStream(this.mysqlSocket.getInputStream(), 16384,
                        propSet.getBooleanProperty(PropertyKey.traceProtocol).getValue(), log);
            } else if (propSet.getBooleanProperty(PropertyKey.useUnbufferedInput).getValue()) {
                rawInputStream = this.mysqlSocket.getInputStream();
            } else {
                rawInputStream = new BufferedInputStream(this.mysqlSocket.getInputStream(), 16384);
            }

            this.mysqlInput = new FullReadInputStream(rawInputStream);
            this.mysqlOutput = new BufferedOutputStream(this.mysqlSocket.getOutputStream(), 16384);
        } catch (IOException ioEx) {
            throw ExceptionFactory.createCommunicationsException(propSet, null, new PacketSentTimeHolder() {
            }, null, ioEx, getExceptionInterceptor());
        }
    }

NativeProtocol完成与mysql的交互,SimplePacketReader,SimplePacketSender完成底层socket的读写

public class SimplePacketSender implements MessageSender<NativePacketPayload> {
    private BufferedOutputStream outputStream;

    public SimplePacketSender(BufferedOutputStream outputStream) {
        this.outputStream = outputStream;
    }
//send方法利用mysql交互协议完成socket写
    public void send(byte[] packet, int packetLen, byte packetSequence) throws IOException {
        PacketSplitter packetSplitter = new PacketSplitter(packetLen);
        while (packetSplitter.nextPacket()) {
            this.outputStream.write(NativeUtils.encodeMysqlThreeByteInteger(packetSplitter.getPacketLen()));
            this.outputStream.write(packetSequence++);
            this.outputStream.write(packet, packetSplitter.getOffset(), packetSplitter.getPacketLen());
        }
        this.outputStream.flush();
    }

    @Override
    public MessageSender<NativePacketPayload> undecorateAll() {
        return this;
    }

    @Override
    public MessageSender<NativePacketPayload> undecorate() {
        return this;
    }
}

/*
 * Copyright (c) 2016, 2021, Oracle and/or its affiliates.
 *
 * This program is free software; you can redistribute it and/or modify it under
 * the terms of the GNU General Public License, version 2.0, as published by the
 * Free Software Foundation.
 *
 * This program is also distributed with certain software (including but not
 * limited to OpenSSL) that is licensed under separate terms, as designated in a
 * particular file or component or in included license documentation. The
 * authors of MySQL hereby grant you an additional permission to link the
 * program and your derivative works with the separately licensed software that
 * they have included with MySQL.
 *
 * Without limiting anything contained in the foregoing, this file, which is
 * part of MySQL Connector/J, is also subject to the Universal FOSS Exception,
 * version 1.0, a copy of which can be found at
 * http://oss.oracle.com/licenses/universal-foss-exception.
 *
 * This program is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
 * FOR A PARTICULAR PURPOSE. See the GNU General Public License, version 2.0,
 * for more details.
 *
 * You should have received a copy of the GNU General Public License along with
 * this program; if not, write to the Free Software Foundation, Inc.,
 * 51 Franklin St, Fifth Floor, Boston, MA 02110-1301  USA
 */

package com.mysql.cj.protocol.a;

import java.io.IOException;
import java.util.Optional;

import com.mysql.cj.Messages;
import com.mysql.cj.conf.RuntimeProperty;
import com.mysql.cj.exceptions.CJPacketTooBigException;
import com.mysql.cj.protocol.MessageReader;
import com.mysql.cj.protocol.SocketConnection;

/**
 * Simple implementation of {@link MessageReader} which handles the receiving of logical MySQL packets from the provided socket input stream.
 * Multi-packets are handled outside of this reader.
 */
public class SimplePacketReader implements MessageReader<NativePacketHeader, NativePacketPayload> {

    protected SocketConnection socketConnection;
    protected RuntimeProperty<Integer> maxAllowedPacket;

    private byte readPacketSequence = -1;

    NativePacketHeader lastHeader = null;
    NativePacketPayload lastMessage = null;

    public SimplePacketReader(SocketConnection socketConnection, RuntimeProperty<Integer> maxAllowedPacket) {
        this.socketConnection = socketConnection;
        this.maxAllowedPacket = maxAllowedPacket;
    }

    @Override
    public NativePacketHeader readHeader() throws IOException {
        if (this.lastHeader == null) {
            return readHeaderLocal();
        }
        NativePacketHeader hdr = this.lastHeader;
        this.lastHeader = null;
        this.readPacketSequence = hdr.getMessageSequence();
        return hdr;
    }

    @Override
    public NativePacketHeader probeHeader() throws IOException {
        this.lastHeader = readHeaderLocal();
        return this.lastHeader;
    }

    private NativePacketHeader readHeaderLocal() throws IOException {
        NativePacketHeader hdr = new NativePacketHeader();

        try {
            this.socketConnection.getMysqlInput().readFully(hdr.getBuffer().array(), 0, NativeConstants.HEADER_LENGTH);
            int packetLength = hdr.getMessageSize();
            if (packetLength > this.maxAllowedPacket.getValue()) {
                throw new CJPacketTooBigException(packetLength, this.maxAllowedPacket.getValue());
            }
        } catch (IOException | CJPacketTooBigException e) {
            try {
                this.socketConnection.forceClose();
            } catch (Exception ex) {
                // ignore
            }
            throw e;
        }

        this.readPacketSequence = hdr.getMessageSequence();
        return hdr;
    }

    @Override
    public NativePacketPayload readMessage(Optional<NativePacketPayload> reuse, NativePacketHeader header) throws IOException {
        if (this.lastMessage == null) {
            return readMessageLocal(reuse, header);
        }
        NativePacketPayload buf = this.lastMessage;
        this.lastMessage = null;
        return buf;
    }

    @Override
    public NativePacketPayload probeMessage(Optional<NativePacketPayload> reuse, NativePacketHeader header) throws IOException {
        this.lastMessage = readMessageLocal(reuse, header);
        return this.lastMessage;
    }

    private NativePacketPayload readMessageLocal(Optional<NativePacketPayload> reuse, NativePacketHeader header) throws IOException {
        try {
            int packetLength = header.getMessageSize();
            NativePacketPayload message;
            if (reuse.isPresent()) {
                message = reuse.get();
                // Set the Buffer to it's original state
                message.setPosition(0);
                // Do we need to re-alloc the byte buffer?
                if (message.getByteBuffer().length < packetLength) {
                    // Note: We actually check the length of the buffer, rather than getBufLength(), because getBufLength()
                    // is not necessarily the actual length of the byte array used as the buffer
                    message.setByteBuffer(new byte[packetLength]);
                }

                // Set the new length
                message.setPayloadLength(packetLength);
            } else {
                message = new NativePacketPayload(new byte[packetLength]);
            }

            // Read the data from the server
            int numBytesRead = this.socketConnection.getMysqlInput().readFully(message.getByteBuffer(), 0, packetLength);
            if (numBytesRead != packetLength) {
                throw new IOException(Messages.getString("PacketReader.1", new Object[] { packetLength, numBytesRead }));
            }
            return message;

        } catch (IOException e) {
            try {
                this.socketConnection.forceClose();
            } catch (Exception ex) {
                // ignore
            }
            throw e;
        }
    }

    @Override
    public byte getMessageSequence() {
        return this.readPacketSequence;
    }

    @Override
    public void resetMessageSequence() {
        this.readPacketSequence = 0;
    }

}