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;
		}

	}

}