一些容易混淆的实战点

@Value，空值，空字符串，"null"问题

@Value("${aaa}") ，即没给默认值，配置文件必须有aaa这个key的配置；
@Value("${aaa:null}") 即给了默认值null，则
　　配置文件写"aaa="，则使用配置文件的值（空字符串），这种情况最终取到的值是空字符串；
　　没有aaa= 这个配置，会使用默认值，且默认值会是"null"，而不是null值

@Value("${aaa:}")

private List<String> aaa；------这个最终得到的值是空数组，而不是null

mybatis查list的结果

如果未查到结果，结果集是new ArrayList()，不是null

Json反序列化时的fail-on-ignored-properties属性

spring中默认是false,就是忽略掉；但是如果是自定义的ObjectMapper是true...看源码

public enum DeserializationFeature implements ConfigFeature {
    USE_BIG_DECIMAL_FOR_FLOATS(false),
    USE_BIG_INTEGER_FOR_INTS(false),
    USE_LONG_FOR_INTS(false),
    USE_JAVA_ARRAY_FOR_JSON_ARRAY(false),
    FAIL_ON_UNKNOWN_PROPERTIES(true),
    FAIL_ON_NULL_FOR_PRIMITIVES(false),
    FAIL_ON_NUMBERS_FOR_ENUMS(false),
    FAIL_ON_INVALID_SUBTYPE(true),
    FAIL_ON_READING_DUP_TREE_KEY(false),
    FAIL_ON_IGNORED_PROPERTIES(false),
    FAIL_ON_UNRESOLVED_OBJECT_IDS(true),
    FAIL_ON_MISSING_CREATOR_PROPERTIES(false),
    FAIL_ON_NULL_CREATOR_PROPERTIES(false),
    FAIL_ON_MISSING_EXTERNAL_TYPE_ID_PROPERTY(true),
    FAIL_ON_TRAILING_TOKENS(false),
    ....
}

自定义的在这里

@Bean
    public ObjectMapper objectMapper() {
        ObjectMapper objectMapper = new ObjectMapper();
        objectMapper.disable(SerializationFeature.WRITE_DATES_AS_TIMESTAMPS);
        objectMapper.disable(DeserializationFeature.ADJUST_DATES_TO_CONTEXT_TIME_ZONE);
        JavaTimeModule javaTimeModule = new JavaTimeModule();
        javaTimeModule.addSerializer(LocalDateTime.class, new LocalDateTimeSerializer(DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss")));
        javaTimeModule.addSerializer(LocalDate.class, new LocalDateSerializer(DateTimeFormatter.ofPattern("yyyy-MM-dd")));
        javaTimeModule.addSerializer(LocalTime.class, new LocalTimeSerializer(DateTimeFormatter.ofPattern("HH:mm:ss")));
        javaTimeModule.addDeserializer(LocalDateTime.class, new LocalDateTimeDeserializer(DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss")));
        javaTimeModule.addDeserializer(LocalDate.class, new LocalDateDeserializer(DateTimeFormatter.ofPattern("yyyy-MM-dd")));
        javaTimeModule.addDeserializer(LocalTime.class, new LocalTimeDeserializer(DateTimeFormatter.ofPattern("HH:mm:ss")));
        objectMapper.registerModule(javaTimeModule);
        objectMapper.configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false);
        return objectMapper;
    }