CharacterEncodingFilter 源码解析以及在 SpringBoot 中的配置

SpringMVC 中有这样一个 Filter 专门处理编码问题的，它是CharacterEncodingFilter。

比如默认给 response 返回设定编码格式为：UTF-8，则可以通过配置 CharacterEncodingFilter 实现。

CharacterEncodingFilter 源码

查看源码，它是一个OncePerRequestFilter，里面有如下几个配置项：

1. encoding：设置的编码格式
2. forceRequestEncoding：是否强制设置请求编码格式为设置的编码格式
3. forceResponseEncoding：是否强制设置返回编码格式为设置的编码格式

源码也很简单，请求会调用到：doFilterInternal方法。

public class CharacterEncodingFilter extends OncePerRequestFilter {

    private String encoding;

    private boolean forceRequestEncoding = false;

    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(String encoding) {
        this.encoding = encoding;
    }
    
    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) {
                request.setCharacterEncoding(encoding);
            }
            if (isForceResponseEncoding()) {
                response.setCharacterEncoding(encoding);
            }
        }
        filterChain.doFilter(request, response);
    }

}

所以在 SpringMVC 项目中使用，可以参考如下配置：

<filter>
    <filter-name>characterEncodingFilter</filter-name>
    <filter-class>org.springframework.web.filter.CharacterEncodingFilter</filter-class>
    <init-param>
        <param-name>encoding</param-name>
        <param-value>UTF-8</param-value>
    </init-param>
    <init-param>
        <param-name>forceEncoding</param-name>
        <param-value>true</param-value>
    </init-param>
</filter>
<filter-mapping>
    <filter-name>characterEncodingFilter</filter-name>
    <url-pattern>/*</url-pattern>
</filter-mapping>

SpringBoot 支持

SpringBoot 对CharacterEncodingFilter 也有支持，在项目启动中可以看到如下日志：

17:03:55.802  INFO 7980 --- : Mapping servlet: 'dispatcherServlet' to [/]
17:03:55.809  INFO 7980 --- : Mapping filter: 'characterEncodingFilter' to: [/*]
17:03:55.810  INFO 7980 --- : Mapping filter: 'hiddenHttpMethodFilter' to: [/*]
17:03:55.810  INFO 7980 --- : Mapping filter: 'httpPutFormContentFilter' to: [/*]
17:03:55.810  INFO 7980 --- : Mapping filter: 'requestContextFilter' to: [/*]

这是因为 SpringBoot 在自动装配时，HttpEncodingAutoConfiguration配置类里配置了该 Filter：

@Configuration
@EnableConfigurationProperties(HttpEncodingProperties.class) // 使用 HttpEncodingProperties 接收配置 
@ConditionalOnWebApplication
@ConditionalOnClass(CharacterEncodingFilter.class)
// 没有配置：spring.http.encoding.enabled 时，默认为：true
@ConditionalOnProperty(prefix = "spring.http.encoding", value = "enabled", matchIfMissing = true)
public class HttpEncodingAutoConfiguration {

    private final HttpEncodingProperties properties;

    public HttpEncodingAutoConfiguration(HttpEncodingProperties properties) {
        this.properties = properties;
    }
    
    // 创建 CharacterEncodingFilter Bean
    @Bean
    @ConditionalOnMissingBean(CharacterEncodingFilter.class)
    public CharacterEncodingFilter characterEncodingFilter() {
        CharacterEncodingFilter filter = new OrderedCharacterEncodingFilter();
        filter.setEncoding(this.properties.getCharset().name());
        filter.setForceRequestEncoding(this.properties.shouldForce(Type.REQUEST));
        filter.setForceResponseEncoding(this.properties.shouldForce(Type.RESPONSE));
        return filter;
    }

    @Bean
    public LocaleCharsetMappingsCustomizer localeCharsetMappingsCustomizer() {
        return new LocaleCharsetMappingsCustomizer(this.properties);
    }

    private static class LocaleCharsetMappingsCustomizer implements EmbeddedServletContainerCustomizer, Ordered {

        private final HttpEncodingProperties properties;

        LocaleCharsetMappingsCustomizer(HttpEncodingProperties properties) {
            this.properties = properties;
        }

        @Override
        public void customize(ConfigurableEmbeddedServletContainer container) {
            if (this.properties.getMapping() != null) {
                container.setLocaleCharsetMappings(this.properties.getMapping());
            }
        }

        @Override
        public int getOrder() {
            return 0;
        }

    }

}

使用 SpringBoot 配置如下：

# 设置的编码，默认为：UTF-8
spring.http.encoding.charset=UTF-8

# 是否启用 CharacterEncodingFilter，如果不配置也代表 true
spring.http.encoding.enabled=true

# 是否强制设置请求和响应的编码格式为设置的编码格式
spring.http.encoding.force=

# 是否强制设置请求的编码格式为设置的编码格式
spring.http.encoding.force-request=

# 是否强制设置响应的编码格式为设置的编码格式
spring.http.encoding.force-response=