杰克逊2和Spring Autowired bean

Question

我的User对象的Jackson序列化遇到问题。有一些带有getter和setter的私有字段。当我做这样的事情时，一切工作正常：

public String json() {
   MyUser user = new MyUser();
   user.setUsername("myName");

   return mapper.writeValueAsString(user); // Valid JSON
}

但是我想用Spring Framework自动连接User对象：

@Autowired
private MyUser user;

public String json() {
    System.out.println(user.getUsername()); // Property set before and it works
    return mapper.writeValueAsString(user); // Error
}

这是行不通的。我有一个错误：

com.fasterxml.jackson.databind.JsonMappingException: No serializer found for class org.apache.juli.OneLineFormatter and no properties discovered to create BeanSerializer (to avoid exception, disable SerializationFeature.FAIL_ON_EMPTY_BEANS) ) (through reference chain: com.piggymetrics.classes.PiggyUser$$EnhancerBySpringCGLIB$$5f23855e["targetSource"]->org.springframework.aop.target.SimpleBeanTargetSource["beanFactory"]->org.springframework.beans.factory.support.DefaultListableBeanFactory["parentBeanFactory"]->org.springframework.beans.factory.support.DefaultListableBeanFactory["beanClassLoader"]->org.apache.catalina.loader.WebappClassLoader["resources"]->org.apache.catalina.webresources.StandardRoot["context"]->org.apache.catalina.core.StandardContext["logger"]->org.apache.juli.logging.DirectJDKLog["logger"]->java.util.logging.Logger["parent"]->java.util.logging.Logger["handlers"]->org.apache.juli.AsyncFileHandler["formatter"])
at com.fasterxml.jackson.databind.ser.impl.UnknownSerializer.failForEmpty(UnknownSerializer.java:59)
at com.fasterxml.jackson.databind.ser.impl.UnknownSerializer.serialize(UnknownSerializer.java:26)

当我尝试忽略这些未知错误时

mapper.disable(SerializationFeature.FAIL_ON_EMPTY_BEANS);

我得到了无限递归：

com.fasterxml.jackson.databind.JsonMappingException: Infinite recursion (StackOverflowError) (through reference chain: org.apache.catalina.core.StandardEngineValve["container"]->org.apache.catalina.core.StandardEngine["pipeline"]->org.apache.catalina.core.StandardPipeline["basic"]->org.apache.catalina.core.StandardEngineValve["container"]
...

看起来Spring在自动装配MyUser实例上做错了什么，因此Jackson无法序列化它。

有办法解决吗？

更新

MyUser类非常简单：

package com.metrics.classes;

import com.metrics.classes.interfaces.User;
import org.springframework.context.annotation.Scope;
import org.springframework.context.annotation.ScopedProxyMode;
import org.springframework.stereotype.Component;

@Component
@Scope(value = "session", proxyMode = ScopedProxyMode.TARGET_CLASS)
public class MyUser implements User {

    private String username;

    public String getUsername() {
        return username;
    }

    public void setUsername(String username) {
        this.username = username;
    }
}

Answer 1

由于您MyUser用作Spring托管的bean，因此Spring将您的对象包装到一个代理中-
因此，在调用时，mapper.writeValueAsString(user);您实际上是在将代理作为参数传递。所述代理包含一些属性，映射器无法序列化。

您可以尝试在序列化之前应用过滤器，以仅包括所需的属性：

ObjectMapper mapper = new ObjectMapper();
SimpleFilterProvider simpleFilterProvider = new SimpleFilterProvider()
    .addFilter("myUser", simpleBeanPropertyFilter.filterOutAllExcept("username"));

mapper.setFilters(filterProvider);
return mapper.writeValueAsString(user);