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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。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 = FALSEcharacter-set-server = utf8mb4collation-server = utf8mb4_unicode_ciinit_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.Driverjdbc.url=jdbc:mysql://localhost:3306/database?useUnicode=true&characterEncoding=utf8&autoReconnect=true&rewriteBatchedStatements=TRUEjdbc.username=rootjdbc.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;
测试连接数据库查看字符编码：
//STEP 1. Import required packagesimport 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 utf8mb4character_set_connection utf8mb4character_set_database utf8mb4character_set_filesystem binarycharacter_set_results utf8mb4character_set_server utf8mb4character_set_system utf8character_sets_dir /usr/share/mysql/charsets/
更多关于mysql 字符集：
本文原文连接: 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： 。 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。