本文原文连接: http://blog.csdn.net/freewebsys/article/details/45537411 转载请注明出处！
1，关于utf8mb4
utf8mb4 is a superset of utf8
utf8mb4兼容utf8，且比utf8能表示更多的字符。
emoji就是表情符号；词义来自日语（えもじ，e-moji，moji在日语中的含义是字符）
表情符号现已普遍应用于手机短信和网络聊天软件。
emoji表情符号，在外国的手机短信里面已经是很流行使用的一种表情。
2，mycat中支持utf8mb4
走了很多多弯路。理论上只要在server.xml的charset设置下就行，但是没有这么简单。直接连接不上了。
同样配置 utf8 gbk是可以的，但是感觉上utf8mb4这个编码太特殊了，mycat判断可能有bug。
终极必杀：修改源代码，org.opencloudb.mysql.nio.MySQLConnection： 450 行。
private static CommandPacket getCharsetCommand(int ci) {
String charset = CharsetUtil.getCharset(ci);
StringBuilder s = new StringBuilder();
LOGGER.info("################## MySQLConnection getCharsetCommand: "+ci+"\t|"+charset);
s.append("SET names utf8mb4 ");//.append(charset);
CommandPacket cmd = new CommandPacket();
cmd.packetId = 0;
cmd.command = MySQLPacket.COM_QUERY;
cmd.arg = s.toString().getBytes();
return cmd;
}解决办法，直接写死连接设置的编码。当然mysql服务器这边也要修改编码。
vi /etc/my.cnf
[client]
default-character-set = utf8mb4
[mysql]
default-character-set = utf8mb4
[mysqld]
character-set-client-handshake = FALSE
character-set-server = utf8mb4
collation-server = utf8mb4_unicode_ci
init_connect=‘SET NAMES utf8mb4‘客户端查看编码
SHOW VARIABLES LIKE ‘character%‘
+--------------------------+--------------------+
| Variable_name | Value |
+--------------------------+--------------------+
| character_set_client | utf8mb4 |
| character_set_connection | utf8mb4 |
| character_set_database | utf8mb4 |
| character_set_filesystem | binary |
| character_set_results | utf8mb4 |
| character_set_server | utf8mb4 |
| character_set_system | utf8 |
+--------------------------+--------------------+
rows in set (0.00 sec)jdbc修改连接：
jdbc.driverClassName=com.mysql.jdbc.Driver
jdbc.url=jdbc:mysql://localhost:3306/database?useUnicode=true&characterEncoding=utf8&autoReconnect=true&rewriteBatchedStatements=TRUE
jdbc.username=root
jdbc.password=password修改数据表：（数据库和表字段修改）
ALTER DATABASE database_name CHARACTER SET = utf8mb4 COLLATE = utf8mb4_unicode_ci;
ALTER TABLE table_name CONVERT TO CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci;
ALTER TABLE table_name CHANGE column_name VARCHAR(191) CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci;http://www.tutorialspoint.com/jdbc/jdbc-select-records.htm
测试连接数据库查看字符编码：
//STEP 1. Import required packages
import java.sql.*;
public class JDBCExample {
// JDBC driver name and database URL
static final String JDBC_DRIVER = "com.mysql.jdbc.Driver";
static final String DB_URL = "jdbc:mysql://localhost/STUDENTS";
// Database credentials
static final String USER = "username";
static final String PASS = "password";
public static void main(String[] args) {
Connection conn = null;
Statement stmt = null;
try{
//STEP 2: Register JDBC driver
Class.forName("com.mysql.jdbc.Driver");
//STEP 3: Open a connection
System.out.println("Connecting to a selected database...");
conn = DriverManager.getConnection(DB_URL, USER, PASS);
System.out.println("Connected database successfully...");
//STEP 4: Execute a query
System.out.println("Creating statement...");
stmt = conn.createStatement();
String sql = " show variables like ‘character%‘ ";
ResultSet rs = stmt.executeQuery(sql);
//STEP 5: Extract data from result set
while (rs.next()) {
//Display values
System.out.print(rs.getString(1));
System.out.print("\t");
System.out.print(rs.getString(2));
System.out.println();
}
rs.close();
}catch(SQLException se){
//Handle errors for JDBC
se.printStackTrace();
}catch(Exception e){
//Handle errors for Class.forName
e.printStackTrace();
}finally{
//finally block used to close resources
try{
if(stmt!=null)
conn.close();
}catch(SQLException se){
}// do nothing
try{
if(conn!=null)
conn.close();
}catch(SQLException se){
se.printStackTrace();
}//end finally try
}//end try
System.out.println("Goodbye!");
}//end main
}//end JDBCExample如果返回utf8mb4即可：
character_set_client utf8mb4
character_set_connection utf8mb4
character_set_database utf8mb4
character_set_filesystem binary
character_set_results utf8mb4
character_set_server utf8mb4
character_set_system utf8
character_sets_dir /usr/share/mysql/charsets/更多关于mysql 字符集：http://www.laruence.com/2008/01/05/12.html
3，总结：
本文原文连接: http://blog.csdn.net/freewebsys/article/details/45537411 转载请注明出处！
需要注意的只有mysql 5.5才支持utf8mb4字符集。
centos安装 mysql 5.5 参考：http://stackoverflow.com/questions/9361720/update-mysql-version-from-5-1-to-5-5-in-centos-6-2
。
mycat设计的还是挺好的，也很稳定的。开源的好处是可以自己研究代码。非常高兴。