杰克逊在写作时忽略了字段 [英] Jackson ignore fields when writing

问题描述

我正在使用杰克逊库从JSON读取此对象：

I'm reading this object from JSON using the Jackson library:

{
    a = "1";
    b = "2";
    c = "3";
}

我正在使用 mapper.readValue解析这个（new JsonFactory（）。createJsonParser（json），MyClass.class）;

现在我想将对象打印到JSON，使用 mapper.writeValueAsString（object），但我想忽略'c'字段。我怎样才能做到这一点？将 @JsonIgnore 添加到字段会阻止在解析时设置字段，不是吗？

Now I want to print the object to JSON, using mapper.writeValueAsString(object), but I want to ignore the 'c' field. How can I achieve this? Adding @JsonIgnore to the field would prevent the field from being set while parsing, wouldn't it?

推荐答案

你不能通过使用公共字段来实现这一点，你必须使用方法（getter / setter）。使用Jackson 1.x，你只需要将 @JsonIgnore 添加到getter方法和没有注释的setter方法，它就可以了。杰克逊2.x，注释解决方案被重新设计，您需要在getter AND @JsonProperty 上放置 @JsonIgnore setter。

You can't do this by using public fields, you have to use methods (getter/setter). With Jackson 1.x, you simply need to add @JsonIgnore to the getter method and a setter method with no annotation, it'll work. Jackson 2.x, annotation resolution was reworked and you will need to put @JsonIgnore on the getter AND @JsonProperty on the setter.

public static class Foo {
    public String a = "1";
    public String b = "2";
    private String c = "3";

    @JsonIgnore
    public String getC() { return c; }

    @JsonProperty // only necessary with Jackson 2.x
    public String setC(String c) { this.c = c; }
}

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