Java乱码问题一直是困扰初学者的一个难题，下面就根据笔者的经验来给大家一个解决方案。我写了一个Demo的web应用，解决了乱码问题，
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1 问题来源
Java的乱码问题，根源在于操作系统、数据库（MySQL）、Web服务器（Tomcat）、页面（JSP）中的编码不一致造成的。例如，mysql的编码是latin1，而页面上字符的编码是GBK，则就会出现乱码问题。
2 解决方案
了解了乱码产生的原因，下面就来看一下如何解决乱码。事实上，只要保证各个环节的编码一致，就不会产生乱码，
所以只要将所有的环节，设置的编码为UTF-8，就不会出现乱码了（为了支持国际化，建议统一设置成UTF-8）。
3 mysql数据库编码的设置（以MySQL 5.0.41为例）
- 查看数据库支持的编码：show character set;
这样可以查看mysql数据库支持的所有编码，其中可以看到有支持utf8编码。
mysql> show character set ;
+----------+-----------------------------+---------------------+--------+
| Charset | Description | Default collation | Maxlen |
+----------+-----------------------------+---------------------+--------+
| big5 | Big5 Traditional Chinese | big5_chinese_ci | 2 |
| dec8 | DEC West European | dec8_swedish_ci | 1 |
| cp850 | DOS West European | cp850_general_ci | 1 |
| hp8 | HP West European | hp8_english_ci | 1 |
| koi8r | KOI8-R Relcom Russian | koi8r_general_ci | 1 |
| latin1 | cp1252 West European | latin1_swedish_ci | 1 |
| latin2 | ISO 8859-2 Central European | latin2_general_ci | 1 |
| swe7 | 7bit Swedish | swe7_swedish_ci | 1 |
| ascii | US ASCII | ascii_general_ci | 1 |
| ujis | EUC-JP Japanese | ujis_japanese_ci | 3 |
| sjis | Shift-JIS Japanese | sjis_japanese_ci | 2 |
| hebrew | ISO 8859-8 Hebrew | hebrew_general_ci | 1 |
| tis620 | TIS620 Thai | tis620_thai_ci | 1 |
| euckr | EUC-KR Korean | euckr_korean_ci | 2 |
| koi8u | KOI8-U Ukrainian | koi8u_general_ci | 1 |
| gb2312 | GB2312 Simplified Chinese | gb2312_chinese_ci | 2 |
| greek | ISO 8859-7 Greek | greek_general_ci | 1 |
| cp1250 | Windows Central European | cp1250_general_ci | 1 |
| gbk | GBK Simplified Chinese | gbk_chinese_ci | 2 |
| latin5 | ISO 8859-9 Turkish | latin5_turkish_ci | 1 |
| armscii8 | ARMSCII-8 Armenian | armscii8_general_ci | 1 |
| utf8 | UTF-8 Unicode | utf8_general_ci | 3 |
| ucs2 | UCS-2 Unicode | ucs2_general_ci | 2 |
| cp866 | DOS Russian | cp866_general_ci | 1 |
| keybcs2 | DOS Kamenicky Czech-Slovak | keybcs2_general_ci | 1 |
| macce | Mac Central European | macce_general_ci | 1 |
| macroman | Mac West European | macroman_general_ci | 1 |
| cp852 | DOS Central European | cp852_general_ci | 1 |
| latin7 | ISO 8859-13 Baltic | latin7_general_ci | 1 |
| cp1251 | Windows Cyrillic | cp1251_general_ci | 1 |
| cp1256 | Windows Arabic | cp1256_general_ci | 1 |
| cp1257 | Windows Baltic | cp1257_general_ci | 1 |
| binary | Binary pseudo charset | binary | 1 |
| geostd8 | GEOSTD8 Georgian | geostd8_general_ci | 1 |
| cp932 | SJIS for Windows Japanese | cp932_japanese_ci | 2 |
| eucjpms | UJIS for Windows Japanese | eucjpms_japanese_ci | 3 |
+----------+-----------------------------+---------------------+--------+
36 rows in set (0.00 sec
- 查看数据库默认的编码： show variables like '%character%'
mysql> show variables like '%character%';
+--------------------------+---------------------------------------+
| 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 | E:\mysql-5.0.41-win32\share\charsets\ |
+--------------------------+---------------------------------------+
8 rows in set (0.00 sec)
可以看到，mysql数据库中，此时有关字符串的设置的参数，其中“character_set_server”为创建数据库是默认的编码，现在需要将其修改为utf8。
- 修改数据库默认的编码：set character_set_server='utf8';
mysql> set character_set_server='utf8';
Query OK, 0 rows affected (0.00 sec)
执行改命令后，可以看到数据库此时的默认编码改为utf8了
mysql> show variables like '%character%';
+--------------------------+---------------------------------------+
| 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 | utf8 |
| character_set_system | utf8 |
| character_sets_dir | E:\mysql-5.0.41-win32\share\charsets\ |
+--------------------------+---------------------------------------+
8 rows in set (0.00 sec)
此时，创建数据库和表如果不指定字符集，则也会使用uft8的编码了。
show create database 数据库名;
show create table 表名;
例如存在这样一个数据库mydbdefault，mydbdefault中有一个表test
mysql> use mydbdefault;
Database changed
mysql> show create database mydbdefault;
+-------------+-----------------------------------------------------------------
-------+
| Database | Create Database
|
+-------------+-----------------------------------------------------------------
-------+
| mydbdefault | CREATE DATABASE `mydbdefault` /*!40100 DEFAULT CHARACTER SET latin1 */ |
+-------------+-----------------------------------------------------------------
-------+
1 row in set (0.00 sec)
数据库mydbdefault的编码为latin1
mysql> show create table test;
+-------+-----------------------------------------------------------------------
-------------------+
| Table | Create Table
|
+-------+-----------------------------------------------------------------------
-------------------+
| test | CREATE TABLE `test` (
`id` int(20) default NULL
) ENGINE=MyISAM DEFAULT CHARSET=latin1 |
+-------+-----------------------------------------------------------------------
-------------------+
1 row in set (0.00 sec)
表的编码为latin1
alter database 数据库名 character set utf8;
alter table 表名 character set utf8;
既然查出数据库和表的编码都不是uft8，所以此时要将数据库和表的字符集改成utf8。
mysql> alter database mydbdefault character set utf8;
Query OK, 1 row affected (0.00 sec)
mysql> show create database mydbdefault;
+-------------+-----------------------------------------------------------------
-----+
| Database | Create Database
|
+-------------+-----------------------------------------------------------------
-----+
| mydbdefault | CREATE DATABASE `mydbdefault` /*!40100 DEFAULT CHARACTER SET utf
8 */ |
+-------------+-----------------------------------------------------------------
-----+
1 row in set (0.00 sec)
mysql> alter table test character set utf8;
Query OK, 0 rows affected (0.03 sec)
Records: 0 Duplicates: 0 Warnings: 0
mysql> show create table test;
+-------+-----------------------------------------------------------------------
-----------------+
| Table | Create Table
|
+-------+-----------------------------------------------------------------------
-----------------+
| test | CREATE TABLE `test` (
`id` int(20) default NULL
) ENGINE=MyISAM DEFAULT CHARSET=utf8 |
+-------+-----------------------------------------------------------------------
-----------------+
1 row in set (0.00 sec)
- 在不知道默认的编码方式的情况下，创建数据库和表时，最好指定字符编码为utf8：
create database 数据库名 character set utf8;
create table 表名 (….) character set utf8;
有关mysql的字符集的命令，可以mysql的参考手册http://dev.mysql.com/doc/refman/5.1/zh/charset.html
4 Tomcat编码的设置（以Tomcat 6.0.14版本为例）
在Tomcat的安装目录下，找到TOMCAT_HOME\conf\server.xml，然后找到以下代码，在其后加上URIEncoding="UTF-8"
<Connector port="8080" protocol="HTTP/1.1"
connectionTimeout="20000"
redirectPort="8443" URIEncoding="UTF-8"/>
5 web应用中编码处理
在web应用中，为了确保提交的字符串为uft-8的，可以编写一个过滤器filter，过滤器的在web.xml中的配置如下：
对应的SetCharacterEncodingFilter类代码如下：
<filter>
<filter-name>Set Character Encoding</filter-name>
<filter-class>
com.fengmanfei.util.SetCharacterEncodingFilter
</filter-class>
<init-param>
<param-name>encoding</param-name>
<param-value>UTF-8</param-value>
</init-param>
</filter>
<filter-mapping>
<filter-name>Set Character Encoding</filter-name>
<url-pattern>/*</url-pattern>
</filter-mapping>
过滤器的代码如下所示：
package com.fengmanfei.util;
import java.io.IOException;
import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
public class SetCharacterEncodingFilter implements Filter {
private String encoding = "UTF-8";
public void doFilter(ServletRequest request, ServletResponse response,
FilterChain chain) throws IOException, ServletException {
request.setCharacterEncoding(encoding);
chain.doFilter(request, response);
}
public void init(FilterConfig filterConfig) throws ServletException {
String s = filterConfig.getInitParameter("encoding");
if (s != null) {
encoding = s;
}
}
public void destroy() {
}
}
其中，关键的是通过过滤器，将request请求设置UTF-8编码
6 数据库连接URL
jdbc:mysql://localhost:3306/mydb?characterEncoding=UTF-8
7 页面中编码处理
在jsp页面上，同时也要设置页面编码方式
<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
8 Eclipse中编码的设置
最后，在使用Eclipse时，要将工作区的编码也设置为UTF-8，选择“Window”|“Preference”|“General”|“Workspace”，将Text file encodeing 改为UTF-8，如图所示：