springboot处理乱码问题原理

我们在用spring-springmvc时，需要配置一个过滤器 CharacterEncodingFilter

CharacterEncodingFilter filter = new OrderedCharacterEncodingFilter();
filter.setEncoding("utf-8");
filter.setForceRequestEncoding(true); //是否对请求对象进行编码过来
filter.setForceResponseEncoding(true); //是否对响应对象做过滤

在springboot中，由于自动装配机制，不需要我们手动配置了，HttpEncodingAutoConfiguration

@Configuration
@EnableConfigurationProperties(HttpProperties.class)
@ConditionalOnWebApplication(type = ConditionalOnWebApplication.Type.SERVLET)
@ConditionalOnClass(CharacterEncodingFilter.class)
@ConditionalOnProperty(prefix = "spring.http.encoding", value = "enabled", matchIfMissing = true)
public class HttpEncodingAutoConfiguration {

    private final HttpProperties.Encoding properties;

    public HttpEncodingAutoConfiguration(HttpProperties properties) {
        this.properties = properties.getEncoding();
    }

    @Bean
    @ConditionalOnMissingBean
    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;
    }
}

由此可见，是否进行编码过滤，都是通过 HttpProperties.Encoding properties进行判断的：

@ConfigurationProperties(prefix = "spring.http")
public class HttpProperties {/**
     * HTTP encoding properties.
     */
    private final Encoding encoding = new Encoding();
/**
     * Configuration properties for http encoding.
     */
    public static class Encoding {

        public static final Charset DEFAULT_CHARSET = StandardCharsets.UTF_8;

        /**
         * Charset of HTTP requests and responses. Added to the "Content-Type" header if
         * not set explicitly.
         */
        private Charset charset = DEFAULT_CHARSET;

        /**
         * Whether to force the encoding to the configured charset on HTTP requests and
         * responses.
         */
        private Boolean force;  //如果这个属性为true就会对请求和响应都进行utft-8编码过滤

        /**
         * Whether to force the encoding to the configured charset on HTTP requests.
         * Defaults to true when "force" has not been specified.
         */
        private Boolean forceRequest; //是否对请求进行过滤

        /**
         * Whether to force the encoding to the configured charset on HTTP responses.
         */
        private Boolean forceResponse; //是否对响应进行过滤

       
　　　　//这个是判断请求或者响应是否要过滤的代码
        public boolean shouldForce(Type type) {
　　　　　　　//根据类型来取配置的请求过滤还是响应过滤　
            Boolean force = (type != Type.REQUEST) ? this.forceResponse
                    : this.forceRequest;  
　　　　　　　//如果没配置，就判断　this.force的值，因为该值对请求和响应都生效
            if (force == null) {
                force = this.force;
            }
　　　　　　　//如果还是没配置，那么默认，请求就会进行过滤　
            if (force == null) {
                force = (type == Type.REQUEST);
            }
            return force;
        }

        public enum Type {

            REQUEST, RESPONSE

        }

    }

}

通过上面 shouldForce(Type type)方法可以知道，在没有相关配置时，默认只会对请求进行过滤，所以要想对响应也进行过滤，需要在yml中进行配置：

spring:
  http:
    encoding:
      charset: UTF-8
      force: true