utf-8 编码可能2个字节、3个字节、4个字节的字符，但是 MySQL 的 utf8 编码只支持3字节的数据，而移动端的表情数据是4个字节的字符。如果直接往采用 utf-8 编码的数据库中插入表情数据，Java 程序中将报SQL异常：

java.sql.SQLException: Incorrect string value: ‘\xF0\x9F\x92\x94’ for column ‘name’ at row 1

at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:1073)

at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:3593)

at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:3525)

at com.mysql.jdbc.MysqlIO.sendCommand(MysqlIO.java:1986)

at com.mysql.jdbc.MysqlIO.sqlQueryDirect(MysqlIO.java:2140)

at com.mysql.jdbc.ConnectionImpl.execSQL(ConnectionImpl.java:2620)

at com.mysql.jdbc.StatementImpl.executeUpdate(StatementImpl.java:1662)

at com.mysql.jdbc.StatementImpl.executeUpdate(StatementImpl.java:1581)

可以对4字节的字符进行编码存储，然后取出来的时候，再进行解码。但是这样做会使得任何使用该字符的地方都要进行编码与解码。

utf8mb4编码是utf8编码的超集，兼容utf8，并且能存储4字节的表情字符。

采用utf8mb4编码的好处是：存储与获取数据的时候，不用再考虑表情字符的编码与解码问题。

更改数据库的编码为utf8mb4:

1. MySQL的版本

utf8mb4 的最低 MySQL 版本支持版本为 5.5.3+，若不是，请升级到较新版本。

2. MySQL驱动

5.1.34 可用,最低不能低于 5.1.13

3. 修改MySQL配置文件

修改 MySQL 配置文件 my.cnf(windows为my.ini)

my.cnf一般在etc/mysql/my.cnf位置。找到后请在以下三部分里添加如下内容：

[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'

4. 重启数据库，检查变量

SHOW VARIABLES WHERE Variable_name LIKE 'character_set_%' OR Variable_name LIKE 'collation%';

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

collation_connection

utf8mb4_unicode_ci

collation_database

utf8mb4_unicode_ci

collation_server

utf8mb4_unicode_ci

collation_connection 、collation_database 、collation_server是什么没关系，但必须保证：

系统变量

描述

character_set_client

(客户端来源数据使用的字符集)

character_set_connection

(连接层字符集)

character_set_database

(当前选中数据库的默认字符集)

character_set_results

(查询结果字符集)

character_set_server

(默认的内部操作字符集)

这几个变量必须是utf8mb4。

5. 数据库连接的配置

数据库连接参数中:

characterEncoding=utf8 会被自动识别为 utf8mb4，也可以不加这个参数，会自动检测。

而 autoReconnect=true 是必须加上的。

6. 将数据库和已经建好的表也转换成utf8mb4

更改数据库编码：

ALTER DATABASE caitu99 CHARACTER SET `utf8mb4` COLLATE `utf8mb4_general_ci`;

更改表编码：

ALTER TABLE `TABLE_NAME` CONVERT TO CHARACTER SET `utf8mb4` COLLATE `utf8mb4_general_ci`;

如有必要，还可以更改列的编码

可以写代码批量进行转换:

//获取所有表

Connection conn = null;

try {

conn = DbUtilsTool.openConn("MySQL", "127.0.0.1", "3306", "caitu99", "root", "root");

String sql = "show tables";

QueryRunner qr = new QueryRunner();

List tblNameList= (List) qr.query(conn, sql, new ColumnListHandler(1));

sql = "ALTER DATABASE caitu99 CHARACTER SET `utf8mb4` COLLATE `utf8mb4_general_ci`";

qr.update(conn,sql);

for (String str:tblNameList) {

sql = "ALTER TABLE "+str+" CONVERT TO CHARACTER SET `utf8mb4` COLLATE `utf8mb4_general_ci`";

qr.update(conn,sql);

}

}

catch (Exception e) {

e.printStackTrace();

throw new RuntimeException(e);

}

finally {

if(conn!=null) {

try {

conn.close();

} catch (SQLException e) {

e.printStackTrace();

}

}

}

DbUtilsTool类：

package com.mysql.chartest;

import java.sql.Connection;

import java.sql.DriverManager;

import java.sql.SQLException;

import java.util.List;

import java.util.Map;

import org.apache.commons.dbutils.BasicRowProcessor;

import org.apache.commons.dbutils.BeanProcessor;

import org.apache.commons.dbutils.QueryRunner;

import org.apache.commons.dbutils.handlers.ArrayHandler;

import org.apache.commons.dbutils.handlers.ArrayListHandler;

import org.apache.commons.dbutils.handlers.BeanHandler;

import org.apache.commons.dbutils.handlers.BeanListHandler;

import org.apache.commons.dbutils.handlers.ColumnListHandler;

import org.apache.commons.dbutils.handlers.KeyedHandler;

import org.apache.commons.dbutils.handlers.MapHandler;

import org.apache.commons.dbutils.handlers.MapListHandler;

import org.apache.commons.dbutils.handlers.ScalarHandler;

public class DbUtilsTool {

private static final QueryRunner runner = new QueryRunner();

/* 打开数据库连接(type: MySQL，Oracle，SQLServer) */

public static Connection openConn(String type, //数据库类型

String host, //主机ip

String port, //主机端口

String name, //数据库名

String username, //用户名

String password)//密码

{

Connection conn = null;

try {

String driver;

String url;

if (type.equalsIgnoreCase("MySQL")) {

driver = "com.mysql.jdbc.Driver";

url = "jdbc:mysql://" + host + ":" + port + "/" + name;

} else if (type.equalsIgnoreCase("Oracle")) {

driver = "oracle.jdbc.driver.OracleDriver";

url = "jdbc:oracle:thin:@" + host + ":" + port + ":" + name;

} else if (type.equalsIgnoreCase("SQLServer")) {

driver = "com.microsoft.jdbc.sqlserver.SQLServerDriver";

url = "jdbc:sqlserver://" + host + ":" + port + ";databaseName=" + name;

} else {

throw new RuntimeException();

}

Class.forName(driver);

conn = DriverManager.getConnection(url, username, password);

} catch (Exception e) {

e.printStackTrace();

}

return conn;

}

/* 关闭数据库连接 */

public static void closeConn(Connection conn) {

try {

if (conn != null) {

conn.close();

}

} catch (Exception e) {

e.printStackTrace();

}

}

/* 查询(返回Array结果) */

public static Object[] queryArray(Connection conn, String sql, Object... params) {

Object[] result = null;

try {

result = runner.query(conn, sql, new ArrayHandler(), params);

} catch (SQLException e) {

e.printStackTrace();

}

return result;

}

/* 查询(返回ArrayList结果) */

public static List queryArrayList(Connection conn, String sql, Object... params) {

List result = null;

try {

result = runner.query(conn, sql, new ArrayListHandler(), params);

} catch (SQLException e) {

e.printStackTrace();

}

return result;

}

/* 查询(返回Map结果) */

public static Map queryMap(Connection conn, String sql, Object... params) {

Map result = null;

try {

result = runner.query(conn, sql, new MapHandler(), params);

} catch (SQLException e) {

e.printStackTrace();

}

return result;

}

/* 查询(返回MapList结果) */

public static List> queryMapList(Connection conn, String sql, Object... params) {

List> result = null;

try {

result = runner.query(conn, sql, new MapListHandler(), params);

} catch (SQLException e) {

e.printStackTrace();

}

return result;

}

/* 查询(返回Bean结果) */

public static T queryBean(Class cls, Map map, Connection conn, String sql, Object... params) {

T result = null;

try {

if (map != null) {

result = runner.query(conn, sql, new BeanHandler(cls, new BasicRowProcessor(new BeanProcessor(map))), params);

} else {

result = runner.query(conn, sql, new BeanHandler(cls), params);

}

} catch (SQLException e) {

e.printStackTrace();

}

return result;

}

/* 查询(返回BeanList结果) */

public static List queryBeanList(Class cls, Map map, Connection conn, String sql, Object... params) {

List result = null;

try {

if (map != null) {

result = runner.query(conn, sql, new BeanListHandler(cls, new BasicRowProcessor(new BeanProcessor(map))), params);

} else {

result = runner.query(conn, sql, new BeanListHandler(cls), params);

}

} catch (SQLException e) {

e.printStackTrace();

}

return result;

}

/* 查询指定列名的值(单条数据) */

public static T queryColumn(String column, Connection conn, String sql, Object... params) {

T result = null;

try {

result = runner.query(conn, sql, new ScalarHandler(column), params);

} catch (SQLException e) {

e.printStackTrace();

}

return result;

}

/* 查询指定列名的值(多条数据) */

public static List queryColumnList(String column, Connection conn, String sql, Object... params) {

List result = null;

try {

result = runner.query(conn, sql, new ColumnListHandler(column), params);

} catch (SQLException e) {

e.printStackTrace();

}

return result;

}

/* 查询指定列名对应的记录映射 */

public static Map> queryKeyMap(String column, Connection conn, String sql, Object... params) {

Map> result = null;

try {

result = runner.query(conn, sql, new KeyedHandler(column), params);

} catch (SQLException e) {

e.printStackTrace();

}

return result;

}

/* 更新(包括UPDATE、INSERT、DELETE，返回受影响的行数) */

public static int update(Connection conn, String sql, Object... params) {

int result = 0;

try {

result = runner.update(conn, sql, params);

} catch (SQLException e) {

e.printStackTrace();

}

return result;

}

}