mysql jdbc 中文亂碼解決方案

對於mysql數據庫而言，解決中文亂碼，能夠從兩個方向考慮，一個是經過修改mysql服務器端的配置文件/etc/mysql/my.cnf來支持中文，好比：

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

可是，修改配置文件須要重啓服務，尤爲是對於已經在線上運行的數據庫或者「老」的數據庫實例（有多是多實例或集羣）而言，顯然經過修改配置文件來操做是不適合的，甚至是不被DBA容許的，一般能想到的辦法是在客戶端或者JDBC鏈接時定製支持中文的編碼格式（一般使用UTF-8），這樣插入數據的時候，讓mysql爲自動爲咱們轉碼，可行的辦法有兩種:

一、若是是經過DriverManager.getConnection(url)編碼方式操做JDBC，能夠在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

二、若是是經過其它數據源，好比DBCP、tomcat-jdbc、c3p0、spring-jdbc、hibernate讀取配置文件，在url中追加useUnicode=true&characterEncoding=UTF-8是不起做用的，而是經過數據源自身的配置生效，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(切換到某個數據庫先後比較)：

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)

能夠看到數據庫robot_classifymark採用的是utf8編碼的，正好對應建立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;

若是想在命令行下插入中文，能夠執行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，能夠在當前命令行下插入中文了，可是，此命令只對當前命令行有效（*），若是想每次登入mysql命令行都生效，一樣須要修改mysql服務器端的配置文件/etc/mysql/my.cnf

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

因此，若是JDBC鏈接時，若是url未指定useUnicode=true&characterEncoding=UTF-8，能夠變相的經過每次執行insert或select語句以前先執行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或者經過上面的數據源配置形式簡潔!