mysql jdbc 中文乱码解决方案

对于mysql数据库而言，解决中文乱码，能够从两个方向考虑，一个是经过修改mysql服务器端的配置文件/etc/mysql/my.cnf来支持中文，好比：

...
[mysql]
default-character-set=utf8
...

可是，修改配置文件须要重启服务，尤为是对于已经在线上运行的数据库或者“老”的数据库实例（有多是多实例或集群）而言，显然经过修改配置文件来操做是不适合的，甚至是不被DBA容许的，一般能想到的办法是在客户端或者JDBC链接时定制支持中文的编码格式（一般使用UTF-8），这样插入数据的时候，让mysql为自动为咱们转码，可行的办法有两种:

一、若是是经过DriverManager.getConnection(url)编码方式操做JDBC，能够在JDBC的url中追加useUnicode=true&characterEncoding=UTF-8解决乱码问题。

jdbc.url=jdbc:mysql://127.0.0.1:3306/mydb?useUnicode=true&characterEncoding=UTF-8

二、若是是经过其它数据源，好比DBCP、tomcat-jdbc、c3p0、spring-jdbc、hibernate读取配置文件，在url中追加useUnicode=true&characterEncoding=UTF-8是不起做用的，而是经过数据源自身的配置生效，好比下列配置：

<!-- Tomcat data source -->
 <bean id="dataSource" class="org.apache.tomcat.jdbc.pool.DataSource">
  <property name="driverClassName" value="${jdbc.driverClassName}" />
  <property name="url" value="${jdbc.url}" />
  <property name="username" value="${jdbc.username}" />
  <property name="password" value="${jdbc.password}" />
  <property name="dbProperties">
    <props>
        <prop key="useUnicode">yes</prop>
        <prop key="characterEncoding">utf8</prop>
    </props>
  </property>
  <!-- Configuration refer to optimizing connection performance -->
  <property name="initialSize" value="10" />
  <property name="maxActive" value="100" />
  <property name="maxIdle" value="50" />
  <property name="minIdle" value="10" />
  <property name="suspectTimeout" value="60" />
  <property name="timeBetweenEvictionRunsMillis" value="30000" />
  <property name="minEvictableIdleTimeMillis" value="60000" />
  <property name="testOnBorrow" value="true" />
  <property name="validationQuery" value="SELECT 1" />
  <property name="validationInterval" value="30000" />
  <!-- End Configuration refer to optimizing connection performance -->
 </bean>

其中：

<props>
      <prop key="useUnicode">yes</prop>
      <prop key="characterEncoding">utf8</prop>
</props>

等价于url中的useUnicode=true&characterEncoding=UTF-8

查看当前数据库的字符集(切换到某个数据库先后比较)：

mysql> show variables like 'char_%';
+--------------------------+----------------------------+
| Variable_name            | Value                      |
+--------------------------+----------------------------+
| character_set_client     | latin1                     |
| character_set_connection | latin1                     |
| character_set_database   | latin1                     |
| character_set_filesystem | binary                     |
| character_set_results    | latin1                     |
| character_set_server     | latin1                     |
| character_set_system     | utf8                       |
| character_sets_dir       | /usr/share/mysql/charsets/ |
+--------------------------+----------------------------+
8 rows in set (0.00 sec)

mysql> use robot_classifymark;
Reading table information for completion of table and column names
You can turn off this feature to get a quicker startup with -A

Database changed
mysql> show variables like 'char_%';
+--------------------------+----------------------------+
| Variable_name            | Value                      |
+--------------------------+----------------------------+
| character_set_client     | latin1                     |
| character_set_connection | latin1                     |
| character_set_database   | utf8                       |
| character_set_filesystem | binary                     |
| character_set_results    | latin1                     |
| character_set_server     | latin1                     |
| character_set_system     | utf8                       |
| character_sets_dir       | /usr/share/mysql/charsets/ |
+--------------------------+----------------------------+
8 rows in set (0.00 sec)

能够看到数据库robot_classifymark采用的是utf8编码的，正好对应建立数据库时指定的编码，对应建库SQL：

CREATE DATABASE IF NOT EXISTS robot_classifymark DEFAULT CHARACTER SET utf8 DEFAULT COLLATE utf8_general_ci;

若是想在命令行下插入中文，能够执行set names utf8，此命令会影响三个参数：

mysql> show variables like 'char_%';
+--------------------------+----------------------------+
| Variable_name            | Value                      |
+--------------------------+----------------------------+
| character_set_client     | latin1                     |
| character_set_connection | latin1                     |
| character_set_database   | utf8                       |
| character_set_filesystem | binary                     |
| character_set_results    | latin1                     |
| character_set_server     | latin1                     |
| character_set_system     | utf8                       |
| character_sets_dir       | /usr/share/mysql/charsets/ |
+--------------------------+----------------------------+
8 rows in set (0.00 sec)

mysql> set names utf8
    -> ;
Query OK, 0 rows affected (0.00 sec)

mysql> show variables like 'char_%';
+--------------------------+----------------------------+
| Variable_name            | Value                      |
+--------------------------+----------------------------+
| character_set_client     | utf8                       |
| character_set_connection | utf8                       |
| character_set_database   | utf8                       |
| character_set_filesystem | binary                     |
| character_set_results    | utf8                       |
| character_set_server     | latin1                     |
| character_set_system     | utf8                       |
| character_sets_dir       | /usr/share/mysql/charsets/ |
+--------------------------+----------------------------+
8 rows in set (0.00 sec)

可见：执行命令set names utf8，影响了三个参数:character_set_client,character_set_connection,character_set_results，如此，能够在当前命令行下插入中文了，可是，此命令只对当前命令行有效（*），若是想每次登入mysql命令行都生效，一样须要修改mysql服务器端的配置文件/etc/mysql/my.cnf

...
[client]
default-character-set=utf8
...

因此，若是JDBC链接时，若是url未指定useUnicode=true&characterEncoding=UTF-8，能够变相的经过每次执行insert或select语句以前先执行set names utf8来插入或查询中文，显然，此方式没有在url中指定useUnicode=true&characterEncoding=UTF-8或者经过上面的数据源配置形式简洁!