@JsonIgnore和@GeneratedValue

忘是亡心i 2022-04-02 07:49 186阅读 0赞

@JsonIgnore注解

1、返回 json 字符串时候，忽略该字段，举栗子

> 我封装一个user对象，里面有name,age这2属性，在age上面加了@JsonIgnore注解，把数据返回前端，json格式的user对象中并不存在age属性；

@Target({ ElementType.ANNOTATION_TYPE, ElementType.METHOD, ElementType.CONSTRUCTOR, ElementType.FIELD})
    @Retention(RetentionPolicy.RUNTIME)
    @JacksonAnnotation
    public @interface JsonIgnore
    { 
        /** * Optional argument that defines whether this annotation is active * or not. The only use for value 'false' if for overriding purposes * (which is not needed often); most likely it is needed for use * with "mix-in annotations" (aka "annotation overrides"). * For most cases, however, default value of "true" is just fine * and should be omitted. */
        boolean value() default true;
    }

注释说，一般用于marker annotation人名的注释

**
 * Marker annotation that indicates that the logical property that
 * the accessor (field, getter/setter method or Creator parameter
 * [of { @link JsonCreator}-annotated constructor or factory method])
 * is to be ignored by introspection-based
 * serialization and deserialization functionality.
 *
 * Annotation only needs to be added to one of the accessors (often
 * getter method, but may be setter, field or creator parameter),
 * if the complete removal of the property is desired.
 * However: if only particular accessor is to be ignored (for example,
 * when ignoring one of potentially conflicting setter methods),
 * this can be done by annotating other not-to-be-ignored accessors
 * with { @link JsonProperty} (or its equivalents). This is considered
 * so-called "split property" case and allows definitions of
 * "read-only" (read from input into POJO) and "write-only" (write
 * in output but ignore on output)
 * 
 * NOTE! As Jackson 2.6, there is a new and improved way to define
 * `read-only` and `write-only` properties, using
 * { @link JsonProperty#access()} annotation: this is recommended over
 * use of separate <code>JsonIgnore</code> and { @link JsonProperty}
 * annotations.
 *
 * For example, a "getter" method that would otherwise denote
 * a property (like, say, "getValue" to suggest property "value")
 * to serialize, would be ignored and no such property would
 * be output unless another annotation defines alternative method to use.
 *
 * When ignoring the whole property, the default behavior if encountering
 * such property in input is to ignore it without exception; but if there
 * is a { @link JsonAnySetter} it will be called instead. Either way,
 * no exception will be thrown.
 *
 * Annotation is usually used just a like a marker annotation, that
 * is, without explicitly defining 'value' argument (which defaults
 * to <code>true</code>): but argument can be explicitly defined.
 * This can be done to override an existing `JsonIgnore` by explicitly
 * defining one with 'false' argument: either in a sub-class, or by
 * using "mix-in annotations".

2、@GeneratedValue 用于主键生成

@Target({ METHOD, FIELD})
 @Retention(RUNTIME)
 
 public @interface GeneratedValue { 
 
 /** * (Optional) The primary key generation strategy * that the persistence provider must use to * generate the annotated entity primary key. */
 GenerationType strategy() default AUTO;
 
 /** * (Optional) The name of the primary key generator * to use as specified in the {@link SequenceGenerator} * or {@link TableGenerator} annotation. * Defaults to the id generator supplied by persistence provider. */
 String generator() default "";
 }

> 源码注释如下

* Provides for the specification of generation strategies for 
 * the values of primary keys. The <code>GeneratedValue</code> 
 * annotation may be applied to a primary key property or
 * field of an entity or mapped superclass in conjunction with 
 * the { @link Id} annotation.
 *
 * <pre>
 *
 * Example 1:
 *
 * @Id
 * @GeneratedValue(strategy=SEQUENCE, generator="CUST_SEQ")
 * @Column(name="CUST_ID")
 * public Long getId() { return id; }
 *
 * Example 2:
 *
 * @Id
 * @GeneratedValue(strategy=TABLE, generator="CUST_GEN")
 * @Column(name="CUST_ID")
 * Long id;
 * </pre>
 *
 * @since Java Persistence 1.0
 */