SpringBoot 配置類整理 （長期保持更新）

如下配置類不需要特意去記憶

一、跨域請求後端解決方案

package cn.gorit.config;

import org.springframework.context.annotation.Configuration;
import org.springframework.web.servlet.config.annotation.CorsRegistry;
import org.springframework.web.servlet.config.annotation.WebMvcConfigurer;

//解決跨域問題
@Configuration
public class CrosConfig implements WebMvcConfigurer {

    @Override
    public void addCorsMappings(CorsRegistry registry) {
        registry.addMapping("/**")
                .allowedOrigins("*")
                .allowedMethods("GET","POST","HEAD","PUT","DELETE")
                .allowCredentials(true)
                .maxAge(3600)
                .allowedHeaders("*");
    }
}

二、使用 Java 編碼解決靜態文件不加載

在 resources 目錄下的 static 的靜態文件給外部訪問

package cn.gorit.config;

import org.springframework.context.annotation.Configuration;
import org.springframework.web.servlet.config.annotation.ResourceHandlerRegistry;
import org.springframework.web.servlet.config.annotation.WebMvcConfigurer;

@Configuration
public class WebMvcConfig implements WebMvcConfigurer {

    @Override
    public void addResourceHandlers(ResourceHandlerRegistry registry) {
        registry
                .addResourceHandler("/static/**")
                .addResourceLocations("classpath:/static/");
    }
}

三、封裝統一返回結果集時，解決返回 null 值問題

當我們想要返回 json 格式數據的時候，難免會出現 null 值得情況，因此加入如下配置即可解決問題，使用默認的 jackson 解決問題。

import com.fasterxml.jackson.core.JsonGenerator;
import com.fasterxml.jackson.databind.JsonSerializer;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.SerializerProvider;
import org.springframework.boot.autoconfigure.condition.ConditionalOnMissingBean;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.Primary;
import org.springframework.http.converter.json.Jackson2ObjectMapperBuilder;

import java.io.IOException;

/**
 * 使用 SpringBoot 默認的 jackjson 解決 統一結果集爲空的情況
 * */

@Configuration
public class NullValueConfiguration {
    
    @Bean
    @Primary
    @ConditionalOnMissingBean(ObjectMapper.class)
    public ObjectMapper jacksonObjectMapper(Jackson2ObjectMapperBuilder builder) {
        ObjectMapper objectMapper = builder.createXmlMapper(false).build();
        objectMapper.getSerializerProvider().setNullValueSerializer(new JsonSerializer<Object>() {
            @Override
            public void serialize(Object o, JsonGenerator jsonGenerator, SerializerProvider serializerProvider) throws IOException, IOException {
                jsonGenerator.writeString("");
            }
        });
        return objectMapper;
    }
}