SpringBoot整合Gson

怼烎@ 2022-05-13 07:06 212阅读 0赞

# 第一步：移除jackson依赖 #

参考代码

<dependency>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-starter-web</artifactId>
    
                
                <exclusions>
                    <exclusion>
                        <groupId>com.fasterxml.jackson.core</groupId>
                        <artifactId>jackson-databind</artifactId>
                    </exclusion>
                </exclusions>
            </dependency>

# 第二步：加入gson依赖 #

参考代码

<dependency>
         <groupId>com.google.code.gson</groupId>
         <artifactId>gson</artifactId>
    </dependency>

# 完成 #

ps：进入WebMvcConfigurationSupport.java可以看到源码

可以看到有这两个常量

private static final boolean jackson2Present =
    			ClassUtils.isPresent("com.fasterxml.jackson.databind.ObjectMapper",
    					WebMvcConfigurationSupport.class.getClassLoader()) &&
    			ClassUtils.isPresent("com.fasterxml.jackson.core.JsonGenerator",
    					WebMvcConfigurationSupport.class.getClassLoader());
    
    private static final boolean gsonPresent =
    			ClassUtils.isPresent("com.google.gson.Gson",
    					WebMvcConfigurationSupport.class.getClassLoader());

一个是我们加入的gson，另一个则是jackson了。

其中还有这样一个方法，用来返回messageConverters

protected final List<HttpMessageConverter<?>> getMessageConverters() {
    		if (this.messageConverters == null) {
    			this.messageConverters = new ArrayList<>();
    			configureMessageConverters(this.messageConverters);
    			if (this.messageConverters.isEmpty()) {
    				addDefaultHttpMessageConverters(this.messageConverters);
    			}
    			extendMessageConverters(this.messageConverters);
    		}
    		return this.messageConverters;
    	}

通过查看addDefaultHttpMessageConverters这个方法，可以看到它是先判断jackson2Present是否存在

存在则往messageConverters中加入MappingJackson2HttpMessageConverter

即如果gson和jackson同时存在则先判断jackson加入MappingJackson2HttpMessageConverter

if (jackson2Present) {
    	Jackson2ObjectMapperBuilder builder = Jackson2ObjectMapperBuilder.json();
        if (this.applicationContext != null) {
    	    builder.applicationContext(this.applicationContext);
        }
            messageConverters.add(new             
        MappingJackson2HttpMessageConverter(builder.build()));
    }
    else if (gsonPresent) {
    	messageConverters.add(new GsonHttpMessageConverter());
    }

因此，如果出现无法排除jackson等特殊情况，可以通过重写extendMessageConverters方法来使getMessageConverters方法返回一个修改过的messageConverters（就是下面这个集合）

private List<HttpMessageConverter<?>> messageConverters;

## 继承WebMvcConfigurationSupport，重写extendMessageConverters方法，再删除其中的MappingJackson2HttpMessageConverter，加入GsonHttpMessageConverter ##

参考代码

@Configuration
    @EnableWebMvc
    public class GsonUtils extends WebMvcConfigurationSupport {
        @Override
        protected void extendMessageConverters(List<HttpMessageConverter<?>> converters) {
            converters.removeIf(httpMessageConverter -> httpMessageConverter instanceof MappingJackson2HttpMessageConverter);
            converters.add(new GsonHttpMessageConverter());
            super.extendMessageConverters(converters);
        }
    }