Spring Boot之自定義JSON轉換器

JSON是先後端數據交互最流行的格式。在目前的項目開發中，常見的JSON的轉換器有三種（json-lib因爲自身的缺陷基本不用，最普遍的仍是Jackson）：

Jackson

在springboot中默認添加了jackson-databind做爲JSON的處理器，不須要配置其餘處理器。若是開發者配置了MappingJackson2HttpMessageConverter則使用開發者本身配置的，不然系統return new MappingJackson2HttpMessageConverter(objectMapper),源碼以下：

@Configuration
class JacksonHttpMessageConvertersConfiguration {
        //中間代碼省略
        @Bean
        @ConditionalOnMissingBean(
            value = {MappingJackson2HttpMessageConverter.class},
            ignoredType = {"org.springframework.hateoas.mvc.TypeConstrainedMappingJackson2HttpMessageConverter", "org.springframework.data.rest.webmvc.alps.AlpsJsonHttpMessageConverter"}
        )
        public MappingJackson2HttpMessageConverter mappingJackson2HttpMessageConverter(ObjectMapper objectMapper) {
            return new MappingJackson2HttpMessageConverter(objectMapper);
        }
    }
}
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Jackson自定義方式:

@Configuration
public class WebMvcConfig implements WebMvcConfigurer{

    @Bean
    MappingJackson2HttpMessageConverter mappingJackson2HttpMessageConverter() {
        MappingJackson2HttpMessageConverter converter = new MappingJackson2HttpMessageConverter();
        converter.setJsonPrefix("aaa>>>");
        return converter;
    }
}
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對於字段忽略和日期格式化等常見需求能夠使用@JsonIgnore和@JsonFormat解決。

---

Gson

springboot默認提供了Gson的自動轉化類GsonHttpMessageConverter,添加依賴後與使用Jackson無異。 使用Gson須要去除默認的jackson-databind並添加Gson依賴：

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-web</artifactId>
    <exclusions>
        <exclusion>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-tomcat</artifactId>
        </exclusion>
        <exclusion>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-json</artifactId>
        </exclusion>
    </exclusions>
</dependency>
<dependency>
    <groupId>com.google.code.gson</groupId>
    <artifactId>gson</artifactId>
</dependency>
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Gson自定義方式:

@Configuration
public class WebMvcConfig implements WebMvcConfigurer{
    @Bean
    GsonHttpMessageConverter gsonHttpMessageConverter() {
        GsonBuilder builder = new GsonBuilder();
        builder.setDateFormat("yyyy-MM-dd");
        return new GsonHttpMessageConverter(builder.create());
    }
}
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---

fastjson

不一樣於jackson以及gson，fastjson要求開發者必須手動配置HttpMessageConverter。首先排除jackson，而後加入gson依賴：

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-web</artifactId>
    <exclusions>
        <exclusion>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-tomcat</artifactId>
        </exclusion>
        <exclusion>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-json</artifactId>
        </exclusion>
    </exclusions>
</dependency>
<dependency>
    <groupId>com.alibaba</groupId>
    <artifactId>fastjosn</artifactId>
    <version>1.2.4</version>
</dependency>
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fastjson自定義方式:
手動配置convert。也能夠重寫configureMessageConverters方法實現對HttpMessageConverter的配置

@Configuration
public class WebMvcConfig implements WebMvcConfigurer{
    @Bean
    FastJsonHttpMessageConverter fastJsonHttpMessageConverter() {
        FastJsonHttpMessageConverter converter = new FastJsonHttpMessageConverter();
        FastJsonConfig config = new FastJsonConfig();
        config.setDateFormat("yyyy/MM/dd");
        converter.setFastJsonConfig(config);
        return converter;
    }
}
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