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 [email protected] 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(); } }