gson配置

1.配置gson替代默认序列化工具

@Configuration
@EnableWebMvc
public class HttpMessageConverterConfig implements WebMvcConfigurer {

    @Autowired
    private GsonHttpMessageConverter gsonHttpMessageConverter;

    /**
     * 注册gson消息转换器
     */
    @Override
    public void configureMessageConverters(
            List<HttpMessageConverter<?>> converters) {
        converters.add(gsonHttpMessageConverter);
    }

}

2.配置gson的信息转换处理

@Component
public class GsonHttpMessageConverter extends AbstractJsonHttpMessageConverter {
    @Autowired
    private GsonExclusionStrategy gsonExclusionStrategy;
    @Autowired
    private JsonSchemaRepo jsonSchemaRepo;

    /**
     * 用于读取定义的类型的资源，将其转化为JSONObject对象
     */
    @Override
    protected Object readInternal(Type resolvedType, Reader reader)
            throws Exception {
        Optional<JsonSchemaEntity> optional = jsonSchemaRepo
                .findById(resolvedType.getTypeName());
        if (optional.isPresent()) {
            // 将reader转换成字符串
            BufferedReader br = new BufferedReader(reader);
            StringBuilder sb = new StringBuilder();
            String line = null;
            while ((line = br.readLine()) != null) {
                sb.append(line);
            }
            String json = sb.toString();
            // json格式校验
            JsonNode schema = new JsonNodeReader().fromReader(
                    new StringReader(optional.get().getJosnSchema()));
            JsonNode data = new JsonNodeReader()
                    .fromReader(new StringReader(json));
            ProcessingReport report = JsonSchemaFactory.byDefault()
                    .getValidator().validate(schema, data);
            if (report.isSuccess()) {
                // 校验通过
                return gsonDeserialize().fromJson(json, resolvedType);
            } else {
                // 校验没有通过
                Iterator<ProcessingMessage> iterator = report.iterator();
                StringBuilder msgsb = new StringBuilder();
                while (iterator.hasNext()) {
                    msgsb.append(iterator.next().getMessage());
                }
                throw new JsonSchemaException("请求的Json格式不正确：{0}", msgsb);
            }
        } else {
            // 不需要校验
            return gsonDeserialize().fromJson(reader, resolvedType);
        }
    }

    /**
     * 用于在推送此种类型的资源时，将JSONObject对象转化为自定义的格式返回给调用者
     * 这里所有的返回JSONObject对象给前端的请求，都会执行此方法
     * 原调用Spring的默认的mappingJackson2HttpMessageConverter来处理
     */
    @Override
    protected void writeInternal(Object o, Type type, Writer writer)
            throws Exception {
        if (type instanceof ParameterizedType) {
            gsonSerialize().toJson(o, type, writer);
        } else {
            gsonSerialize().toJson(o, writer);
        }

    }

    /**
     * Gson基础配置
     *
     * @return
     */
    private GsonBuilder gsonBuilder() {
        GsonBuilder b = new GsonBuilder();
        // 注册特殊类型格式数据适配器
        b.registerTypeAdapter(LocalDateTime.class,
                new CustomLocalDateTypeAdapter());
        return b;
    }

    /**
     * 序列化Gson配置
     *
     * @return
     */
    private Gson gsonSerialize() {
        return gsonBuilder().setExclusionStrategies(gsonExclusionStrategy)
                .create();
    }

    /**
     * 反序列化Gson配置
     *
     * @return
     */
    private Gson gsonDeserialize() {
        return gsonBuilder().create();
    }

}

3.序列化排除策略

@Component
public class GsonExclusionStrategy implements ExclusionStrategy {

    @Override
    public boolean shouldSkipField(FieldAttributes f) {
        if (f.getAnnotation(Expose.class) != null
                && !f.getAnnotation(Expose.class).serialize()) {
            // 如果被Expose注解，且Expose的serialize为false的情况下，不序列化
            return true;
        } else {
            return false;
        }

    }

    @Override
    public boolean shouldSkipClass(Class<?> clazz) {
        return false;
    }

}

4.自定义特殊格式数据适配器

         4.1 第一种方式，实现JsonDeserializer和JsonSerializer接口

public class LocalDateTypeAdapter implements JsonDeserializer<LocalDateTime>,
        JsonSerializer<LocalDateTime> {
    private static final DateTimeFormatter FORMAT = DateTimeFormatter.ISO_DATE_TIME;

    @Override
    public JsonElement serialize(LocalDateTime src, Type typeOfSrc,
            JsonSerializationContext context) {
        return new JsonPrimitive(src.format(FORMAT));
    }

    @Override
    public LocalDateTime deserialize(JsonElement json, Type typeOfT,
            JsonDeserializationContext context) throws JsonParseException {
        return LocalDateTime.parse(json.getAsString(), FORMAT);
    }

}

         4.2 第二种方式，继承TypeAdapter类

public class CustomLocalDateTypeAdapter extends TypeAdapter<LocalDateTime> {

    private static final DateTimeFormatter FORMAT = DateTimeFormatter.ISO_DATE_TIME;

    @Override
    public void write(JsonWriter out, LocalDateTime value) throws IOException {
        if (value == null) {
            out.nullValue();
        } else {
            out.value(value.format(FORMAT));
        }
    }

    @Override
    public LocalDateTime read(JsonReader in) throws IOException {
        if (in.peek() == null) {
            return null;
        }
        String str = in.nextString();
        LocalDateTime date = LocalDateTime.parse(str, FORMAT);
        return date;
    }

}