JSONMappingException-无法反序列化Java对象

• Z时代
• 2024-01-10
• 分类：问答

使用ObjectMapper取消序列化对象时出现以下错误：

JSONMappingException无法构造org.springframework.data.Page的实例，问题：抽象类型只能用其他类型信息实例化。

我正在尝试将JSON字符串序列化为org.springframework.data.Page表示类型页面的Spring数据对象T。

该User班是一个简单的POJO与first和last名称。我要反序列化的JSON字符串是：

{
    "content": [
        {
            "firstname": "John",
            "lastname": "Doe"
        },
        {
            "firstname": "Jane",
            "lastname": "Doe"
        }
    ],
    "size": 2,
    "number": 0,
    "sort": [
        {
            "direction": "DESC",
            "property": "timestamp",
            "ascending": false
        }
    ],
    "totalPages": 150,
    "numberOfElements": 100,
    "totalElements": 15000,
    "firstPage": true,
    "lastPage": false
}

这将导致异常：

Page<User> userPage = (Page<User>) new ObjectMapper().mapToJavaObject(json, new TypeReference<Page<User>>(){};

由于Page是Spring对象，因此无法修改它，我认为这与我在别处看到此问题的方式有些不同。有什么想法吗？

回答：

我最终使用了类似的东西，按照@Perception的建议创建了一个bean：

import java.util.ArrayList;
import java.util.List;
import org.springframework.data.domain.PageImpl;
import org.springframework.data.domain.PageRequest;
import org.springframework.data.domain.Sort;
public class PageImplBean<T> extends PageImpl<T> {
    private static final long serialVersionUID = 1L;
    private int number;
    private int size;
    private int totalPages;
    private int numberOfElements;
    private long totalElements;
    private boolean previousPage;
    private boolean firstPage;
    private boolean nextPage;
    private boolean lastPage;
    private List<T> content;
    private Sort sort;
    public PageImplBean() {
        super(new ArrayList<T>());
    }
    public int getNumber() {
        return number;
    }
    public void setNumber(int number) {
        this.number = number;
    }
    public int getSize() {
        return size;
    }
    public void setSize(int size) {
        this.size = size;
    }
    public int getTotalPages() {
        return totalPages;
    }
    public void setTotalPages(int totalPages) {
        this.totalPages = totalPages;
    }
    public int getNumberOfElements() {
        return numberOfElements;
    }
    public void setNumberOfElements(int numberOfElements) {
        this.numberOfElements = numberOfElements;
    }
    public long getTotalElements() {
        return totalElements;
    }
    public void setTotalElements(long totalElements) {
        this.totalElements = totalElements;
    }
    public boolean isPreviousPage() {
        return previousPage;
    }
    public void setPreviousPage(boolean previousPage) {
        this.previousPage = previousPage;
    }
    public boolean isFirstPage() {
        return firstPage;
    }
    public void setFirstPage(boolean firstPage) {
        this.firstPage = firstPage;
    }
    public boolean isNextPage() {
        return nextPage;
    }
    public void setNextPage(boolean nextPage) {
        this.nextPage = nextPage;
    }
    public boolean isLastPage() {
        return lastPage;
    }
    public void setLastPage(boolean lastPage) {
        this.lastPage = lastPage;
    }
    public List<T> getContent() {
        return content;
    }
    public void setContent(List<T> content) {
        this.content = content;
    }
    public Sort getSort() {
        return sort;
    }
    public void setSort(Sort sort) {
        this.sort = sort;
    }
    public PageImpl<T> pageImpl() {
        return new PageImpl<T>(getContent(), new PageRequest(getNumber(),
                getSize(), getSort()), getTotalElements());
    }
}

然后修改您的代码以使用具体的类并获取PageImpl：

@SuppressWarnings("unchecked")
Page<User> userPage = ((PageImplBean<User>)new ObjectMapper().readValue(json, new TypeReference<PageImplBean<User>>() {})).pageImpl();

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