即使使用@JsonIgnoreProperties

时间:2019-03-05 17:41:16

标签: java jackson stack-overflow mixins self-reference

我试图将带有jackson的DefaultMutableTreeNode对象序列化为json字符串。因此,我需要使用一种混合类抽象类,该类是DefaultMutableTreeNode类的代理。这可能是由于自参考字段,但我无法识别它们。

混合类:

@JsonIgnoreProperties(ignoreUnknown = true)
public abstract class DefaultMutableTreeNodeMixIn {

    @JsonCreator
    public DefaultMutableTreeNodeMixIn(@JsonProperty Object userObject) {};

    @JsonCreator
    public DefaultMutableTreeNodeMixIn(@JsonProperty Object userObject, 
    @JsonProperty boolean allowsChildren) {};

    @JsonProperty("childCount")
    abstract int getChildCount();

    @JsonProperty("depth")
    abstract int getDepth();

    @JsonProperty("firstChild")
    abstract TreeNode getFirstChild();

    @JsonProperty("firstLeaf")
    abstract DefaultMutableTreeNode getFirstLeaf();

    @JsonProperty("lastChild")
    abstract TreeNode getLastChild();

    @JsonProperty("lastLeaf")
    abstract DefaultMutableTreeNode getLastLeaf();

    @JsonProperty("leafCount")
    abstract int getLeafCount();

    @JsonProperty("level")
    abstract int getLevel();

    @JsonProperty("nextLeaf")
    abstract DefaultMutableTreeNode getNextLeaf();

    @JsonProperty("nextNode")
    abstract DefaultMutableTreeNode getNextNode();

    @JsonProperty("nextSibling")
    abstract DefaultMutableTreeNode getNextSibling();

    @JsonProperty("parent")
    abstract TreeNode getParent();

    @JsonProperty("path")
    abstract TreeNode[] getPath();

    @JsonProperty("previousLeaf")
    abstract DefaultMutableTreeNode getPreviousLeaf();

    @JsonProperty("previousNode")
    abstract DefaultMutableTreeNode getPreviousNode();

    @JsonProperty("previousSibling")
    abstract DefaultMutableTreeNode getPreviousSibling();

    @JsonProperty("siblingCount")
    abstract int getSiblingCount();

    @JsonProperty("isLeaf")
    abstract boolean isLeaf();

    @JsonProperty("isRoot")
    abstract boolean isRoot();
}

ObjectMapper:

ObjectMapper mapper = new ObjectMapper();
mapper.addMixIn(DefaultMutableTreeNode.class,DefaultMutableTreeNodeMixIn.class);
String json = mapper.writerWithDefaultPrettyPrinter().writeValueAsString(serverFileTree);
System.out.println(json);

(serverFileTree是类型为DefaultMutableTreeNode的对象)

错误跟踪:

at com.fasterxml.jackson.databind.ser.std.ObjectArraySerializer.serializeContents(ObjectArraySerializer.java:252)
at com.fasterxml.jackson.databind.ser.std.ObjectArraySerializer.serialize(ObjectArraySerializer.java:213)
at com.fasterxml.jackson.databind.ser.std.ObjectArraySerializer.serialize(ObjectArraySerializer.java:22)
at com.fasterxml.jackson.databind.ser.BeanPropertyWriter.serializeAsField(BeanPropertyWriter.java:727)
at com.fasterxml.jackson.databind.ser.std.BeanSerializerBase.serializeFields(BeanSerializerBase.java:719)
at com.fasterxml.jackson.databind.ser.BeanSerializer.serialize(BeanSerializer.java:155) [...]
Caused by: java.lang.StackOverflowError
at java.lang.ClassLoader.defineClass1(Native Method)
at java.lang.ClassLoader.defineClass(Unknown Source)
at java.security.SecureClassLoader.defineClass(Unknown Source)
at java.net.URLClassLoader.defineClass(Unknown Source)
at java.net.URLClassLoader.access$100(Unknown Source)
at java.net.URLClassLoader$1.run(Unknown Source)
at java.net.URLClassLoader$1.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(Unknown Source)
at java.lang.ClassLoader.loadClass(Unknown Source)
at sun.misc.Launcher$AppClassLoader.loadClass(Unknown Source)
at java.lang.ClassLoader.loadClass(Unknown Source)
at com.fasterxml.jackson.databind.ser.std.BeanSerializerBase.serializeFields(BeanSerializerBase.java:737)
... 1011 more

2 个答案:

答案 0 :(得分:0)

如Jackson的文档所述:https://fasterxml.github.io/jackson-annotations/javadoc/2.6/com/fasterxml/jackson/annotation/JsonProperty.html

  

public @interface JsonProperty

     

标记注释,可用于将非静态方法定义为   逻辑属性的“ setter”或“ getter”(取决于其   签名)或要使用的非静态对象字段(序列化,   反序列化)作为逻辑属性。

我确实认为您注释的方法不是属性的setter或getter。

例如:

@JsonProperty("previousNode")
    abstract DefaultMutableTreeNode getPreviousNode();

此方法似乎没有获得属性,而是计算节点。尝试删除方法上的所有注释,看看是否可以解决问题。

答案 1 :(得分:0)

当您开始遍历其getters方法时,此类将生成循环。要打破它们,您需要使用JsonBackReference批注。您的mixin可能看起来像这样:

@JsonIgnoreProperties(ignoreUnknown = true)
abstract class DefaultMutableTreeNodeMixIn {

    @JsonCreator
    public DefaultMutableTreeNodeMixIn(@JsonProperty Object userObject) {
    }

    @JsonCreator
    public DefaultMutableTreeNodeMixIn(@JsonProperty Object userObject, @JsonProperty boolean allowsChildren) {
    }

    @JsonProperty("childCount")
    abstract int getChildCount();

    @JsonProperty("depth")
    abstract int getDepth();

    @JsonProperty("firstChild")
    @JsonBackReference
    abstract TreeNode getFirstChild();

    @JsonProperty("firstLeaf")
    @JsonBackReference
    abstract DefaultMutableTreeNode getFirstLeaf();

    @JsonProperty("lastChild")
    @JsonBackReference
    abstract TreeNode getLastChild();

    @JsonProperty("lastLeaf")
    @JsonBackReference
    abstract DefaultMutableTreeNode getLastLeaf();

    @JsonProperty("leafCount")
    abstract int getLeafCount();

    @JsonProperty("level")
    abstract int getLevel();

    @JsonProperty("nextLeaf")
    abstract DefaultMutableTreeNode getNextLeaf();

    @JsonProperty("nextNode")
    abstract DefaultMutableTreeNode getNextNode();

    @JsonProperty("nextSibling")
    abstract DefaultMutableTreeNode getNextSibling();

    @JsonProperty("parent")
    abstract TreeNode getParent();

    @JsonProperty("path")
    @JsonBackReference
    abstract TreeNode[] getPath();

    @JsonProperty("previousLeaf")
    abstract DefaultMutableTreeNode getPreviousLeaf();

    @JsonProperty("previousNode")
    abstract DefaultMutableTreeNode getPreviousNode();

    @JsonProperty("previousSibling")
    abstract DefaultMutableTreeNode getPreviousSibling();

    @JsonProperty("siblingCount")
    abstract int getSiblingCount();

    @JsonProperty("isLeaf")
    abstract boolean isLeaf();

    @JsonProperty("isRoot")
    abstract boolean isRoot();
}

但是最好最好的OOP方法是创建新的POJO,它代表您的树已准备好进行序列化且没有循环。