@JsonIgnoreProperties(ignoreUnknown = true) 说明

static class Book {

String name;

String price;

}

例一

这样一个类，如果json 字符串中的字段数量多于类的字段，如：

String bookJson3 = "{\"name\":\"d2\", \"price\":\"1\", \"sn\":\"222\"}";

Book b3 = mapper.readValue(bookJson3, Book.class);

那么报错如下：

com.fasterxml.jackson.databind.exc.UnrecognizedPropertyException: Unrecognized field

"sn" (class com.example.demo.DemoApplicationTests2$Book),

not marked as ignorable (2 known properties: "price", "name"])

at [Source: (String)"{"name":"d2", "price":"1", "sn":"222"}"; line: 1, column: 34]

(through reference chain: com.example.demo.DemoApplicationTests2$Book["sn"])

给Book 类增加注解：

@JsonIgnoreProperties(ignoreUnknown = true)

可以解决这个问题。

例二

如果 json 字符串中的字段少了是可以正常工作的，如

String bookJson = "{\"name\":\"dd\"}";

Book b = mapper.readValue(bookJson, Book.class);

System.out.println(b.name);

System.out.println(b.price);

输出为：

dd

null

例三

b = new Book();

b.name = "hhg";

System.out.println(mapper.writeValueAsString(b));

以上代码可以正常工作，输出为：

{"name":"hhg","price":null}