mysql jdbc 中文亂碼解決方案

對於mysql數據庫而言，解決中文亂碼，可以從兩個方向考慮，一個是通過修改mysql服務器端的配置文件/etc/mysql/my.cnf來支持中文，比如：

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

但是，修改配置文件需要重啟服務，尤其是對於已經在線上運行的數據庫或者“老”的數據庫實例（有可能是多實例或集群）而言，顯然通過修改配置文件來操作是不適合的，甚至是不被DBA允許的，通常能想到的辦法是在客戶端或者JDBC連接時定制支持中文的編碼格式（通常使用UTF-8），這樣插入數據的時候，讓mysql為自動為我們轉碼，可行的辦法有兩種:

1、如果是通過DriverManager.getConnection(url)編碼方式操作JDBC，可以在JDBC的url中追加useUnicode=true&characterEncoding=UTF-8解決亂碼問題。

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

2、如果是通過其它數據源，比如DBCP、tomcat-jdbc、c3p0、spring-jdbc、hibernate讀取配置文件，在url中追加useUnicode=true&characterEncoding=UTF-8是不起作用的，而是通過數據源自身的配置生效，比如下列配置：

<!-- 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>

等價於url中的useUnicode=true&characterEncoding=UTF-8

查看當前數據庫的字符集(切換到某個數據庫前后比較)：

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)

可以看到數據庫robot_classifymark采用的是utf8編碼的，正好對應創建數據庫時指定的編碼，對應建庫SQL：

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

如果想在命令行下插入中文，可以執行set names utf8，此命令會影響三個參數：

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)

可見：執行命令set names utf8，影響了三個參數:character_set_client,character_set_connection,character_set_results，如此，可以在當前命令行下插入中文了，但是，此命令只對當前命令行有效（*），如果想每次登入mysql命令行都生效，同樣需要修改mysql服務器端的配置文件/etc/mysql/my.cnf

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

所以，如果JDBC連接時，如果url未指定useUnicode=true&characterEncoding=UTF-8，可以變相的通過每次執行insert或select語句之前先執行set names utf8來插入或查詢中文，顯然，此方式沒有在url中指定useUnicode=true&characterEncoding=UTF-8或者通過上面的數據源配置形式簡潔!