更改MySQL数据库的编码为utf8mb4

抄自《更改MySQL数据库的编码为utf8mb4》。

utf-8 编码可能2个字节、3个字节、4个字节的字符,但是 MySQLutf8 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_connectioncollation_databasecollation_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。
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();

  /* 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<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;
  }

  /* 查询(返回Map结果) */
  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;
  }

  /* 查询(返回MapList结果) */
  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;
  }

  /* 查询(返回Bean结果) */
  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;
  }

  /* 查询(返回BeanList结果) */
  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;
  }

  /* 查询指定列名的值(单条数据) */
  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;
  }

  /* 查询指定列名的值(多条数据) */
  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;
  }

  /* 查询指定列名对应的记录映射 */
  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;
  }

  /* 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;
  }
}

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