SpringMVC 乱码解决

1. GET请求乱码

1.1. 终极解决方案：修改server.xml的URIEncoding

如果使用tomcat插件，在<configuration>标签中设置<uriEncoding>属性即可

<build>
    <plugins>
        <plugin>
            <groupId>org.apache.tomcat.maven</groupId>
            <artifactId>tomcat7-maven-plugin</artifactId>
            <version>2.2</version>
            <configuration>
                <port>8080</port>
                <path>/</path>
                <!-- 设置uriEncoding -->
                <uriEncoding>UTF-8</uriEncoding>
            </configuration>
        </plugin>
    </plugins>
</build>

如果是tomcat服务器，则修改conf/server.xml

<!-- 找到设置port="8080"的那个标签，添加URIEncoding="UTF-8"即可 -->
<Connector port="8080" protocol="HTTP/1.1"
    connectionTimeout="20000"
    redirectPort="8443"
    URIEncoding="UTF-8" />

2. POST请求乱码

2.1. 方式1：原生API

@GetMapping("/test")
public void haha(HttpServletRequest request) throws Exception {
    // 在第1次获取请求参数之前设置
    request.setCharacterEncoding("UTF-8");
    // 再获取参数，就不会乱码了
    String username = request.getParameter("username");
}

2.2. 方式2：CharacterEncodingFilter

使用原生API，每一个POST方法都要写一遍
request.setCharacterEncoding("UTF-8")，太麻烦。干脆统一写一个Filter，所有的请求先统一执行一遍该方法，保证编码能被解析。

这个Filter不用我们亲自写，SpringMVC内置了CharacterEncodingFilter，这个过滤器不仅能设置POST请求的编码，还能设置响应的编码

<filter>
    <filter-name>characterEncodingFilter</filter-name>
    <filter-class>org.springframework.web.filter.CharacterEncodingFilter</filter-class>
    <init-param>
        <!-- 设置请求数据的编码为UTF-8 -->
        <param-name>encoding</param-name>
        <param-value>UTF-8</param-value>
    </init-param>
    <init-param>
        <!-- 设置响应数据的编码为UTF-8（该编码取决于上面设置的encoding属性） -->
        <param-name>forceEncoding</param-name>
        <param-value>true</param-value>
    </init-param>
</filter>
<filter-mapping>
    <!-- 拦截所有请求 -->
    <filter-name>characterEncodingFilter</filter-name>
    <url-pattern>/*</url-pattern>
</filter-mapping>

3. CharacterEncodingFilter的设置顺序最好放在首位

CharacterEncodingFilter会设置POST请求的编码

request.setCharacterEncoding(encoding)

设置POST请求的编码，这条语句应该要写在获取参数之前，这样才能保证读取的参数编码格式是正确的

// 先设置编码
request.setCharacterEncoding(encoding)
// 再获取参数
request.getParameter("username");

有的过滤器，如HiddenHttpMethodFilter，查看源码可知有通过request.getParameter()获取参数。如果HiddenHttpMethodFilter配置顺序在CharacterEncodingFilter之前，就会出现先获取参数，再设置POST请求编码的情况。所以为了避免这种情况发生，在web.xml中，CharacterEncodingFilter应该配置在其它Filter之前

4. CharacterEncodingFilter源码分析

public class CharacterEncodingFilter extends OncePerRequestFilter {
    /** 在web.xml中配置encoding，就会设置该值 */
    @Nullable
    private String encoding;

    /**
     * 在web.xml中设置forceEncoding的值，会同时设置forceRequestEncoding/forceResponseEncoding
     */
    
    /** request是否强制使用encoding编码 */
    private boolean forceRequestEncoding = false;

    /** response是否强制使用encoding编码 */
    private boolean forceResponseEncoding = false;

    public CharacterEncodingFilter() {
    }

    public CharacterEncodingFilter(String encoding) {
        this(encoding, false);
    }

    public CharacterEncodingFilter(String encoding, boolean forceEncoding) {
        this(encoding, forceEncoding, forceEncoding);
    }

    public CharacterEncodingFilter(String encoding, boolean forceRequestEncoding, boolean forceResponseEncoding) {
        Assert.hasLength(encoding, "Encoding must not be empty");
        this.encoding = encoding;
        this.forceRequestEncoding = forceRequestEncoding;
        this.forceResponseEncoding = forceResponseEncoding;
    }

    public void setEncoding(@Nullable String encoding) {
        this.encoding = encoding;
    }

    @Nullable
    public String getEncoding() {
        return this.encoding;
    }

    public void setForceEncoding(boolean forceEncoding) {
        this.forceRequestEncoding = forceEncoding;
        this.forceResponseEncoding = forceEncoding;
    }

    public void setForceRequestEncoding(boolean forceRequestEncoding) {
        this.forceRequestEncoding = forceRequestEncoding;
    }

    public boolean isForceRequestEncoding() {
        return this.forceRequestEncoding;
    }

    public void setForceResponseEncoding(boolean forceResponseEncoding) {
        this.forceResponseEncoding = forceResponseEncoding;
    }

    public boolean isForceResponseEncoding() {
        return this.forceResponseEncoding;
    }

    @Override
    protected void doFilterInternal(HttpServletRequest request, HttpServletResponse response, FilterChain filterChain)
            throws ServletException, IOException {
        String encoding = getEncoding();
        if (encoding != null) {
            if (isForceRequestEncoding() || request.getCharacterEncoding() == null) {
                // 设置POST请求的编码
                request.setCharacterEncoding(encoding);
            }
            if (isForceResponseEncoding()) {
                // 设置响应编码
                response.setCharacterEncoding(encoding);
            }
        }
        // 放行所有请求
        filterChain.doFilter(request, response);
    }
}