Spring Data JPA整合REST客户端Feign时: 分页查询的反序列化报错的问题

Type definition error: [simple type, class org.springframework.data.domain.Page];
nested exception is com.fasterxml.jackson.databind.exc.InvalidDefinitionException:
Cannot construct instance of `org.springframework.data.domain.Page` (no Creators, like default construct, exist):
abstract types either need to be mapped to concrete types, have custom deserializer, or contain additional type information
 at [Source: (PushbackInputStream); line: 1, column: 48] (through reference chain:
 com.core.domain.dto.ResultDTO["data"]->com.trade.manager.rest.search.domain.dto.PCShopSearchProductDTO["products"]), feign.codec.DecodeException
feign.codec.DecodeException:
Type definition error:
[simple type, class org.springframework.data.domain.Page]; nested exception is com.fasterxml.jackson.databind.exc.InvalidDefinitionException:
Cannot construct instance of `org.springframework.data.domain.Page` (no Creators, like default construct, exist):
abstract types either need to be mapped to concrete types, have custom deserializer, or contain additional type information
 at [Source: (PushbackInputStream); line: 1, column: 48] (through reference chain:
 com.core.domain.dto.ResultDTO["data"]->com.trade.manager.rest.search.domain.dto.PCShopSearchProductDTO["products"])
    at feign.SynchronousMethodHandler.decode(SynchronousMethodHandler.java:180) ~[feign-core-10.1.0.jar!/:na]
    at feign.SynchronousMethodHandler.executeAndDecode(SynchronousMethodHandler.java:140) ~[feign-core-10.1.0.jar!/:na]
    at feign.SynchronousMethodHandler.invoke(SynchronousMethodHandler.java:78) ~[feign-core-10.1.0.jar!/:na]
    at feign.ReflectiveFeign$FeignInvocationHandler.invoke(ReflectiveFeign.java:103) ~[feign-core-10.1.0.jar!/:na]
    at com.sun.proxy.$Proxy161.searchProductShopPC(Unknown Source) ~[na:na]

Spring Data JPA的Page接口, 定义了分页的基本操作, 用起来很是方便. Page接口在SimpleJpaRepository中用得比较广泛, 例如: org.springframework.data.jpa.repository.support.SimpleJpaRepository#findAll

@Override
public <S extends T> Page<S> findAll(Example<S> example, Pageable pageable) {
    ExampleSpecification<S> spec = new ExampleSpecification<S>(example);
    Class<S> probeType = example.getProbeType();
    TypedQuery<S> query = getQuery(new ExampleSpecification<S>(example), probeType, pageable);
    return pageable == null ? new PageImpl<S>(query.getResultList()) : readPage(query, probeType, pageable, spec);
}  

该查询返回一个Page实例, 具体的实现是org.springframework.data.domain.PageImpl.

问题就出在这个PageImpl对象, 正常情况下没有任何问题, 但是如果这个对象通过Feign中转时, 就会出现无法反序列化的错误.

究其原因, 是PageImpl没有无参构造, 其超类Chunk也没有无参构造; 导致反序列化失败.

解决的方法有两种, 一是自定义反序列化, 比较麻烦.
另一种办法就是自定义Page, 放弃Spring自带的PageImpl, 这就解决了反序列化的问题. 笔者使用的是后一种方法.
这是笔者自定义的Page实现, 与Spring无关, 可以在任何项目中通用:

import java.io.Serializable;
import java.util.ArrayList;
import java.util.Collections;
import java.util.Iterator;
import java.util.List;  

/**
 * Page operations.
 *
 * @auther rickgong@iteye.com on 2017/3/17.
 * @see org.springframework.data.domain.Page
 */
public class Page<T> implements Iterable<T>, Serializable {
    private static final long serialVersionUID = -3720998571176536865L;
    private List<T> content = new ArrayList<>();
    private long total;
    private int pageNo;
    private int pageSize;  

    public Page() {
    }  

    public Page(List<T> content, long total, int pageNo, int pageSize) {
        this.content = content;
        this.total = total;
        this.pageNo = pageNo;
        this.pageSize = pageSize;
    }  

    /**
     * Returns if there is a previous page.
     *
     * @return if there is a previous page.
     */
    public boolean hasPrevious() {
        return getPageNo() > 0;
    }  

    /**
     * Returns if there is a next page.
     *
     * @return if there is a next page.
     */
    public boolean hasNext() {
        return getPageNo() + 1 < getTotalPage();
    }  

    /**
     * Returns whether the current page is the first one.
     *
     * @return whether the current page is the first one.
     */
    public boolean isFirst() {
        return !hasPrevious();
    }  

    /**
     * Returns whether the current  page is the last one.
     *
     * @return whether the current  page is the last one.
     */
    boolean isLast() {
        return !hasNext();
    }  

    /**
     * Returns the total amount of elements of all pages.
     *
     * @return the total amount of elements of all pages.
     */
    public long getTotal() {
        return total;
    }  

    public void setTotal(long total) {
        this.total = total;
    }  

    /**
     * Returns the number of total pages.
     *
     * @return the number of total pages
     */
    public int getTotalPage() {
        return getPageSize() == 0 ? 1 : (int) Math.ceil((double) total / (double) getPageSize());
    }  

    /**
     * Returns the page content as unmodifiable {@link List}.
     *
     * @return Returns the page content as unmodifiable {@link List}
     */
    public List<T> getContent() {
        return Collections.unmodifiableList(content);
    }  

    public void setContent(List<T> content) {
        this.content = content;
    }  

    /**
     * Returns whether the current page has content.
     *
     * @return whether the current page has content.
     */
    public boolean hasContent() {
        return getContentSize() > 0;
    }  

    /**
     * Returns the number of elements on current page.
     *
     * @return the number of elements on current page.
     */
    public int getContentSize() {
        return content.size();
    }  

    /**
     * Returns the number of items of each page.
     *
     * @return the number of items of each page
     */
    public int getPageSize() {
        return pageSize;
    }  

    public void setPageSize(int pageSize) {
        this.pageSize = pageSize;
    }  

    /**
     * Returns the number of current page. (Zero-based numbering.)
     *
     * @return the number of current page.
     */
    public int getPageNo() {
        return pageNo;
    }  

    /**
     * Set the number of current page. (Zero-based numbering.)
     */
    public void setPageNo(int pageNo) {
        this.pageNo = pageNo;
    }  

    @Override
    public Iterator<T> iterator() {
        return getContent().iterator();
    }
} 

https://www.iteye.com/blog/rickgong-2363789