自定义 Jackson 注解与禁用某一特定的注解 | 隔叶黄莺 Yanbin Blog

2015-08-03 | 阅读(7,085)

Jackson 是 Playfrmework 2 中默认的 JSON 处理框架，先前是 GSON，JSON 是 Playframework 中的第一等公民，可见 Jackson 在 Playframewok 中的重要地位。Jackson 提供了一系列的注解可用，像 @JsonIgnore, @JsonProperty, @JsonUnwrapped, @JsonFilter 等。人的需求总是很难得到满足，所以免不了还是要定义自己的注解。比如有这样一个需求，JavaBean 中被 @MaskField(这个即将成为我第一个自定义的注解) 标记的属性或 getter 方法，总是输出为 ******, 无此标记的属性或方法输出原始值。

我尝试过 @JsonFilter 或是单纯的自定义 JsonSerializer, 并不怎么如意。本人最终的实现方式涉及到

@JacksonAnnotationsInside -- 用来创建自己的 @MaskField 注解
JsonSerializer -- 被 @MaskField 标记的字段采用自定义的 JsonSerializer 来序列化
JacksonAnnotationIntrospector -- 禁用某一特定的注解，这样可以在做任意时候启用或禁用 @MaskField

再次重复需求，对于下面的 Person 类生成的对象

class Person {

  public String name  = "Yanbin";

  public String getPhone () {
    return "(312)666-8888";
  }

  public int age = 100;

  @JsonProperty("city")
  public String location = "Chicago";

}

class Person {

public String name = "Yanbin";

public String getPhone () {

return "(312)666-8888";

}

public int age = 100;

@JsonProperty("city")

public String location = "Chicago";

}

想要对于某些用户生成

{"name":"Yanbin","age":"******","city":"Chicago","phone":"******"}

其他用户生成

{"name":"Yanbin","age":100,"city":"Chicago"}

即有条件的隐藏某些敏感信息。

希望自定义 @MaskField 来标 name 属性和 getPhone() 方法。

定义 @MaskField

@Retention(RetentionPolicy.RUNTIME)
@Target({ElementType.FIELD, ElementType.METHOD})
@JacksonAnnotationsInside
@JsonSerialize(using = MaskFieldSerializer.class)
@interface MaskField {
}

@Retention(RetentionPolicy.RUNTIME)

@Target({ElementType.FIELD, ElementType.METHOD})

@JacksonAnnotationsInside

@JsonSerialize(using = MaskFieldSerializer.class)

@interface MaskField {

}

上面指示了标记为 @MaskField 字段或 getter 方法奖应用 MaskFieldSerializer 为序列化，总是输出为 ******

MaskFieldSerializer 类

class MaskFieldSerializer extends JsonSerializer<Object> {

  @Override
  public void serialize(Object value, JsonGenerator jgen, SerializerProvider provider)
    throws IOException {
    jgen.writeString("******");
  }
}

class MaskFieldSerializer extends JsonSerializer<Object> {

@Override

public void serialize(Object value, JsonGenerator jgen, SerializerProvider provider)

throws IOException {

jgen.writeString("******");

}

现在把 @MaskField 应用到 Person 类

class Person {

  public String name  = "Yanbin";

  @MaskField
  public String phone () {
    return "(312)666-8888";
  }

  @MaskField
  public int age = 100;

  @JsonProperty("city")
  public String location = "Chicago";

}

class Person {

public String name = "Yanbin";

@MaskField

public String phone () {

return "(312)666-8888";

}

@MaskField

public int age = 100;

@JsonProperty("city")

public String location = "Chicago";

}

用代码测试一下

ObjectMapper maskMapper = new ObjectMapper();
System.out.println(maskMapper.writeValueAsString(new Person()));

1 2	ObjectMapper maskMapper = new ObjectMapper(); System.out.println(maskMapper.writeValueAsString(new Person()));

输出结果没错了，就是

{"name":"Yanbin","age":"******","city":"Chicago","phone":"******"}

凡是标记了 @MaskField 的字段或 getter 方法最终输出统统为 ******, 还记得还有个需求是对于某些时候还希望看到原貌，即

{"name":"Yanbin","age":100,"city":"Chicago"}

也就是有时要只禁用 @MaskField 注解。Jackson 可以调用

maskMapper.configure(MapperFeature.USE_ANNOTATIONS, false);

来禁用所有的注解，那么像 @JsonProperty, @JsonIgnore 这样的注解如何是好，肯定不能一棍子打死，所以这里只是需要适时的把 @MaskField 禁用即可。这时候要用到 JacksonAnnotationIntrospector 来选择某个 Annotation 来禁用了。

因而自定义 DisablingMaskFieldIntrospector

class DisablingMaskFieldIntrospector extends JacksonAnnotationIntrospector {

  @Override
  public boolean isAnnotationBundle(Annotation ann) {
    if (ann.annotationType().equals(MaskField.class)) {
      return false;
    } else {
      return super.isAnnotationBundle(ann);
    }
  }

}

class DisablingMaskFieldIntrospector extends JacksonAnnotationIntrospector {

@Override

public boolean isAnnotationBundle(Annotation ann) {

if (ann.annotationType().equals(MaskField.class)) {

return false;

} else {

return super.isAnnotationBundle(ann);

}

如果是 MaskField 就 return false, 禁用 @MaskField 注解

该告诉你的 ObjectMapper 使用这个自定义 AnnotationIntrospector，下面的测试代码

ObjectMapper showAllMapper = new ObjectMapper();
showAllMapper.setAnnotationIntrospector(new DisablingMaskFieldIntrospector());
System.out.println(showAllMapper.writeValueAsString(new Person()));

ObjectMapper showAllMapper = new ObjectMapper();

showAllMapper.setAnnotationIntrospector(new DisablingMaskFieldIntrospector());

System.out.println(showAllMapper.writeValueAsString(new Person()));

输出为

{"name":"Yanbin","age":100,"city":"Chicago"}

也就是要不要采用 DisablingMaskFieldIntrospector 就决定了我们禁止还是启用 @MaskField 注解的功能。

浪费点篇幅，上面完整的代码如下

import com.fasterxml.jackson.annotation.*;
import com.fasterxml.jackson.core.*;
import com.fasterxml.jackson.databind.*;
import com.fasterxml.jackson.databind.annotation.JsonSerialize;
import com.fasterxml.jackson.databind.introspect.JacksonAnnotationIntrospector;

import java.io.IOException;
import java.lang.annotation.*;

public class TestJacksonAnnotation {

  private static ObjectMapper maskMapper = new ObjectMapper();

  private static ObjectMapper showAllMapper = new ObjectMapper() {{
    setAnnotationIntrospector(new DisablingMaskFieldIntrospector());
  }};

  public static void main(String[] args) throws JsonProcessingException {
    System.out.println(maskMapper.writeValueAsString(new Person()));
    System.out.println(showAllMapper.writeValueAsString(new Person()));
  }
}

class Person {

  public String name  = "Yanbin";

  @MaskField
  public String phone () {
    return "(312)666-8888";
  }

  @MaskField
  public int age = 100;

  @JsonProperty("city")
  public String location = "Chicago";

}

class MaskFieldSerializer extends JsonSerializer<Object> {

  @Override
  public void serialize(Object value, JsonGenerator jgen, SerializerProvider provider)
    throws IOException {
    jgen.writeString("******");
  }
}

@Retention(RetentionPolicy.RUNTIME)
@Target({ElementType.FIELD, ElementType.METHOD})
@JacksonAnnotationsInside
@JsonSerialize(using = MaskFieldSerializer.class)
@interface MaskField {

}

class DisablingMaskFieldIntrospector extends JacksonAnnotationIntrospector {

  @Override
  public boolean isAnnotationBundle(Annotation ann) {
    if (ann.annotationType().equals(MaskField.class)) {
      return false;
    } else {
      return super.isAnnotationBundle(ann);
    }
  }

}

import com.fasterxml.jackson.annotation.*;

import com.fasterxml.jackson.core.*;

import com.fasterxml.jackson.databind.*;

import com.fasterxml.jackson.databind.annotation.JsonSerialize;

import com.fasterxml.jackson.databind.introspect.JacksonAnnotationIntrospector;

import java.io.IOException;

import java.lang.annotation.*;

public class TestJacksonAnnotation {

private static ObjectMapper maskMapper = new ObjectMapper();

private static ObjectMapper showAllMapper = new ObjectMapper() {{

setAnnotationIntrospector(new DisablingMaskFieldIntrospector());

}};

public static void main(String[] args) throws JsonProcessingException {

System.out.println(maskMapper.writeValueAsString(new Person()));

System.out.println(showAllMapper.writeValueAsString(new Person()));

}

class Person {

public String name = "Yanbin";

@MaskField

public String phone () {

return "(312)666-8888";

}

@MaskField

public int age = 100;

@JsonProperty("city")

public String location = "Chicago";

}

class MaskFieldSerializer extends JsonSerializer<Object> {

@Override

public void serialize(Object value, JsonGenerator jgen, SerializerProvider provider)

throws IOException {

jgen.writeString("******");

}

@Retention(RetentionPolicy.RUNTIME)

@Target({ElementType.FIELD, ElementType.METHOD})

@JacksonAnnotationsInside

@JsonSerialize(using = MaskFieldSerializer.class)

@interface MaskField {

}

class DisablingMaskFieldIntrospector extends JacksonAnnotationIntrospector {

@Override

public boolean isAnnotationBundle(Annotation ann) {

if (ann.annotationType().equals(MaskField.class)) {

return false;

} else {

return super.isAnnotationBundle(ann);

}

执行后输出为

{"name":"Yanbin","age":"******","city":"Chicago","phone":"******"}
{"name":"Yanbin","age":100,"city":"Chicago"}

实际的操作就是根据不同的条件使用 maskMapper 或是 showAllMapper 来进行序列化。

参考：1. https://github.com/swagger-api/swagger-core/issues/982
2. http://stackoverflow.com/questions/12921812/create-a-custom-jackson-annotation

本文链接 https://yanbin.blog/customize-jackson-annotation-and-disable-specific-annotation/, 来自隔叶黄莺 Yanbin Blog

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