解决com.fasterxml.jackson.databind.JsonMappingException: No suitable

出现com.fasterxml.jackson.databind.JsonMappingException: No suitable 的情况有很多种，具体情况具体对待。

原因一：

在使用jackson 进行json字符串转java bean的时候出现如下错误，

com.fasterxml.jackson.databind.JsonMappingException: No suitable constructor found for type [simple type, class org.test.Library]: can not instantiate from JSON object (need to add/enable type information?)  at [Source: java.io.StringReader@d1831; line: 1, column: 2]
    at com.fasterxml.jackson.databind.JsonMappingException.from(JsonMappingException.java:164)
    at com.fasterxml.jackson.databind.deser.BeanDeserializerBase.deserializeFromObjectUsingNonDefault(BeanDeserializerBase.java:983)
    at com.fasterxml.jackson.databind.deser.BeanDeserializer.deserializeFromObject(BeanDeserializer.java:276)
    at com.fasterxml.jackson.databind.deser.BeanDeserializer.deserialize(BeanDeserializer.java:121)
    at com.fasterxml.jackson.databind.ObjectMapper._readMapAndClose(ObjectMapper.java:2888)
    at com.fasterxml.jackson.databind.ObjectMapper.readValue(ObjectMapper.java:2034)



原因java bean中没有提供无参的构造函数，如下
public class Library { 

    private String name; 
      
    private List<Book> bookList ; 
    //添加无参的构造器
    public Library(){
    }
    
    public Library(String name){
    this.name = name; 
    }
    
    public String getName() { 
        return name; 
    }
    public void setName(String name) { 
        this.name = name; 
    }

    public List<Book> getBookList() { 
        return bookList; 
    } 
  
    public void setBookList(List<Book> bookList) { 
        this.bookList = bookList; 
    }
}