utf-8编码可能1个字节、2个字节、3个字节、4个字节的字符，但是MySQL的utf8编码只支持最多3字节的数据，也就是说mysql最开始的时候，对utf-8的支持是不完整的。而emoji表情字符是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。
为了支持完整的utf-8编码，mysql推出了utf8mb4，它是mysql平台上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。
但必须保证下面几个变量必须是utf8mb4。
| 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) |
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<String> tblNameList= (List<String>) 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();
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;
}
public static void closeConn(Connection conn) {
try {
if (conn != null) {
conn.close();
}
} catch (Exception e) {
e.printStackTrace();
}
}
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;
}
public static List<Object[]> queryArrayList(Connection conn, String sql, Object... params) {
List<Object[]> result = null;
try {
result = runner.query(conn, sql, new ArrayListHandler(), params);
} catch (SQLException e) {
e.printStackTrace();
}
return result;
}
public static Map<String, Object> queryMap(Connection conn, String sql, Object... params) {
Map<String, Object> result = null;
try {
result = runner.query(conn, sql, new MapHandler(), params);
} catch (SQLException e) {
e.printStackTrace();
}
return result;
}
public static List<Map<String, Object>> queryMapList(Connection conn, String sql, Object... params) {
List<Map<String, Object>> result = null;
try {
result = runner.query(conn, sql, new MapListHandler(), params);
} catch (SQLException e) {
e.printStackTrace();
}
return result;
}
public static <T> T queryBean(Class<T> cls, Map<String, String> map, Connection conn, String sql, Object... params) {
T result = null;
try {
if (map != null) {
result = runner.query(conn, sql, new BeanHandler<T>(cls, new BasicRowProcessor(new BeanProcessor(map))), params);
} else {
result = runner.query(conn, sql, new BeanHandler<T>(cls), params);
}
} catch (SQLException e) {
e.printStackTrace();
}
return result;
}
public static <T> List<T> queryBeanList(Class<T> cls, Map<String, String> map, Connection conn, String sql, Object... params) {
List<T> result = null;
try {
if (map != null) {
result = runner.query(conn, sql, new BeanListHandler<T>(cls, new BasicRowProcessor(new BeanProcessor(map))), params);
} else {
result = runner.query(conn, sql, new BeanListHandler<T>(cls), params);
}
} catch (SQLException e) {
e.printStackTrace();
}
return result;
}
public static <T> T queryColumn(String column, Connection conn, String sql, Object... params) {
T result = null;
try {
result = runner.query(conn, sql, new ScalarHandler<T>(column), params);
} catch (SQLException e) {
e.printStackTrace();
}
return result;
}
public static <T> List<T> queryColumnList(String column, Connection conn, String sql, Object... params) {
List<T> result = null;
try {
result = runner.query(conn, sql, new ColumnListHandler<T>(column), params);
} catch (SQLException e) {
e.printStackTrace();
}
return result;
}
public static <T> Map<T, Map<String, Object>> queryKeyMap(String column, Connection conn, String sql, Object... params) {
Map<T, Map<String, Object>> result = null;
try {
result = runner.query(conn, sql, new KeyedHandler<T>(column), params);
} catch (SQLException e) {
e.printStackTrace();
}
return result;
}
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;
}
}
以上为个人经验，希望能给大家一个参考，也希望大家多多支持我们。
