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概况

ColumnDefinition包属于服务端返回ResultSet时的其中一部分包，用于描述结果集的字段信息。

mysql通信报文结构

ColumnDefinition包

Payload

lenenc_str     cataloglenenc_str     schemalenenc_str     tablelenenc_str     org_tablelenenc_str     namelenenc_str     org_namelenenc_int     length of fixed-length fields [0c]2              character set4              column length1              type2              flags1              decimals2              filler [00] [00]  if command was COM_FIELD_LIST {
     lenenc_int     length of default-valuesstring[$len]   default values  }

更多详情 ：

ColumnCount包类

/** *  * 
column definition command packet.
 * @author  * 
seaboat
 * 
email: 849586227@qq.com
 * 
blog: http://blog.csdn.net/wangyangzhizhou
 * @version 1.0 * @see http://dev.mysql.com/doc/internals/en/com-query-response.html#column-definition */public class ColumnDefinitionPacket extends MySQLPacket {
         private static final byte[] DEFAULT_CATALOG = "def".getBytes();    private static final byte NEXT_LENGTH = 0x0c;    private static final byte[] FILLER = { 00, 00 };    public byte[] catalog = DEFAULT_CATALOG;// always "def"    public byte[] schema;    public byte[] table;    public byte[] orgTable;    public byte[] name;    public byte[] orgName;    public byte nextLength = NEXT_LENGTH;// always 0x0c    public int charsetSet;    public long length;    public int type;    public int flags;    public byte decimals;    public byte[] filler = FILLER;    public byte[] defaultValues;    public void read(byte[] data) {        MySQLMessage mm = new MySQLMessage(data);        this.packetLength = mm.readUB3();        this.packetId = mm.read();        this.catalog = mm.readBytesWithLength();        this.schema = mm.readBytesWithLength();        this.table = mm.readBytesWithLength();        this.orgTable = mm.readBytesWithLength();        this.name = mm.readBytesWithLength();        this.orgName = mm.readBytesWithLength();        this.nextLength = mm.read();        this.charsetSet = mm.readUB2();        this.length = mm.readUB4();        this.type = mm.read() & 0xff;        this.flags = mm.readUB2();        this.decimals = mm.read();        this.filler = mm.readBytes(2);        if (mm.hasRemaining()) {            this.defaultValues = mm.readBytesWithLength();        }    }    @Override    public void write(ByteBuffer buffer) {        int size = calcPacketSize();        BufferUtil.writeUB3(buffer, size);        buffer.put(packetId);        BufferUtil.writeWithLength(buffer, catalog, (byte) 0);        BufferUtil.writeWithLength(buffer, schema, (byte) 0);        BufferUtil.writeWithLength(buffer, table, (byte) 0);        BufferUtil.writeWithLength(buffer, orgTable, (byte) 0);        BufferUtil.writeWithLength(buffer, name, (byte) 0);        BufferUtil.writeWithLength(buffer, orgName, (byte) 0);        buffer.put(NEXT_LENGTH);        BufferUtil.writeUB2(buffer, charsetSet);        BufferUtil.writeUB4(buffer, length);        buffer.put((byte) (type & 0xff));        BufferUtil.writeUB2(buffer, flags);        buffer.put(decimals);        buffer.put(FILLER);        if (defaultValues != null) {            //only use for show columns            BufferUtil.writeWithLength(buffer, defaultValues);        }    }    @Override    public int calcPacketSize() {        int size = (catalog == null ? 1 : BufferUtil.getLength(catalog));        size += (schema == null ? 1 : BufferUtil.getLength(schema));        size += (table == null ? 1 : BufferUtil.getLength(table));        size += (orgTable == null ? 1 : BufferUtil.getLength(orgTable));        size += (name == null ? 1 : BufferUtil.getLength(name));        size += (orgName == null ? 1 : BufferUtil.getLength(orgName));        size += 13;        if (defaultValues != null) {            size += BufferUtil.getLength(defaultValues);        }        return size;    }    @Override    protected String getPacketInfo() {        return "MySQL Column Definition Packet";    }}

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