Spring Boot 运行原理 - 实例分析（HttpEncodingAutoConfiguration）

在了解了Spring Boot的运作原理和主要注解后，现在来简单的分析一个Spring Boot内置的自动配置功能：http的编码配置。

我们在常规项目中配置Http编码的时候是在web.xml添加一个filter,如：

<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>

自动配置要满足两个条件：

1. 能配置CharacterEncodingFilter这个Bean；
2. 能配置encoding和forceEncoding两个参数；

1 配置参数

在前面我们讲述了类型安全配置，Spring Boot也是基于这一点来实现的，这里的配置类可以在application.properties中直接设置，源码如下：

package org.springframework.boot.autoconfigure.web;

import java.nio.charset.Charset;
import java.util.Locale;
import java.util.Map;

import org.springframework.boot.context.properties.ConfigurationProperties;

@ConfigurationProperties(prefix = "spring.http.encoding")// 在application.properties中配置的前缀是spring.http.encoding
public class HttpEncodingProperties {

  public static final Charset DEFAULT_CHARSET = Charset.forName("UTF-8"); 

  private Charset charset = DEFAULT_CHARSET; // 默认的编码方式

  private Boolean force;

  private Boolean forceRequest;

  private Boolean forceResponse;

  private Map<Locale, Charset> mapping;

  public Charset getCharset() {
    return this.charset;
  }

  public void setCharset(Charset charset) {
    this.charset = charset;
  }

  public boolean isForce() {
    return Boolean.TRUE.equals(this.force);
  }

  public void setForce(boolean force) {
    this.force = force;
  }

  public boolean isForceRequest() {
    return Boolean.TRUE.equals(this.forceRequest);
  }

  public void setForceRequest(boolean forceRequest) {
    this.forceRequest = forceRequest;
  }

  public boolean isForceResponse() {
    return Boolean.TRUE.equals(this.forceResponse);
  }

  public void setForceResponse(boolean forceResponse) {
    this.forceResponse = forceResponse;
  }

  public Map<Locale, Charset> getMapping() {
    return this.mapping;
  }

  public void setMapping(Map<Locale, Charset> mapping) {
    this.mapping = mapping;
  }

  boolean shouldForce(Type type) {
    Boolean force = (type == Type.REQUEST ? this.forceRequest : this.forceResponse);
    if (force == null) {
      force = this.force;
    }
    if (force == null) {
      force = (type == Type.REQUEST);
    }
    return force;
  }

  enum Type {

    REQUEST, RESPONSE

  }

}

2 配置Bean

通过调用上述配置并根据条件配置CharacterEncodingFilter的Bean，看源码：

package org.springframework.boot.autoconfigure.web;

import org.springframework.boot.autoconfigure.EnableAutoConfiguration;
import org.springframework.boot.autoconfigure.condition.ConditionalOnClass;
import org.springframework.boot.autoconfigure.condition.ConditionalOnMissingBean;
import org.springframework.boot.autoconfigure.condition.ConditionalOnProperty;
import org.springframework.boot.autoconfigure.condition.ConditionalOnWebApplication;
import org.springframework.boot.autoconfigure.web.HttpEncodingProperties.Type;
import org.springframework.boot.context.embedded.ConfigurableEmbeddedServletContainer;
import org.springframework.boot.context.embedded.EmbeddedServletContainerCustomizer;
import org.springframework.boot.context.properties.EnableConfigurationProperties;
import org.springframework.boot.web.filter.OrderedCharacterEncodingFilter;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.core.Ordered;
import org.springframework.web.filter.CharacterEncodingFilter;

@Configuration
@EnableConfigurationProperties(HttpEncodingProperties.class) // 开启属性注入
@ConditionalOnWebApplication
@ConditionalOnClass(CharacterEncodingFilter.class) // 当CharacterEncodingFilter在类路劲的条件下
@ConditionalOnProperty(prefix = "spring.http.encoding", value = "enabled", matchIfMissing = true)// 当设置spring.http.encoding=enabled的情况下，如果没有设置默认是true，即符合条件
public class HttpEncodingAutoConfiguration {

  private final HttpEncodingProperties properties;

  public HttpEncodingAutoConfiguration(HttpEncodingProperties properties) {
    this.properties = properties;
  }

  @Bean// 使用java方式配置CharacterEncodingFilter的Bean
  @ConditionalOnMissingBean(CharacterEncodingFilter.class)// 当容器中没有这个Bean
  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;
    }

  }

}