我們如何DefaultMutableTreeNode使用 Jackson 將 Swing 序列化/反序列化到 JSON 或從 JSON 序列化/反序列化？有一個相關的問題 How to serialize DefaultMutableTreeNode (Java) to JSON? . 但它要求 Gson，而不是 Jackson（僅用于序列化，而不用于反序列化）。對于DefaultMutableTreeNodeJackson 的默認序列化/序列化不起作用，原因有很多：它包含再次是DefaultMutableTreeNode對象的子項。但它沒有規范的 getter 和 setter 方法（如getChildren()and setChildren(...)）。它包含反向引用（通過方法getParent(), getRoot(), getPath()），這將導致序列化期間的無限遞歸和 StackOverflow。它有許多不需要序列化的冗余 getter 方法（如isLeaf(), getNextSibling(), , ...），因為它們是從其他屬性派生的。getLastChild()
1 回答
呼如林
TA貢獻1798條經驗 獲得超3個贊
您可以ObjectMapper使用 a 自定義 Jackson'sJsonSerializer并JsonDeserializer專門用于將 a 轉換DefaultMutableTreeNode為 JSON，反之亦然。
ObjectMapper objectMapper = new ObjectMapper()
.registerModule(new SimpleModule()
.addSerializer(DefaultMutableTreeNode.class, new DefaultMutableTreeNodeSerializer())
.addDeserializer(DefaultMutableTreeNode.class, new DefaultMutableTreeNodeDeserializer()))
.enable(SerializationFeature.INDENT_OUTPUT);
下面DefaultMutableTreeNodeSerializer負責將 a 轉換DefaultMutableTreeNode為 JSON。它將allowsChildren,userObject和children of寫入DefaultMutableTreeNodeJSON。它不寫它parent，因為那會導致無限遞歸和 StackOverflowError。相反，父子關系被編碼在 JSON 輸出的嵌套結構中。
public class DefaultMutableTreeNodeSerializer extends JsonSerializer<DefaultMutableTreeNode> {
@Override
public void serialize(DefaultMutableTreeNode node, JsonGenerator gen, SerializerProvider serializers)
throws IOException {
gen.writeStartObject();
gen.writeBooleanField("allowsChildren", node.getAllowsChildren());
gen.writeObjectField("userObject", node.getUserObject());
if (node.getChildCount() > 0)
gen.writeObjectField("children", Collections.list(node.children()));
// Don't write node.getParent(), it would lead to infinite recursion.
gen.writeEndObject();
}
}
為了測試，您可以序列化 sample 的根節點JTree，然后再次反序列化。
JTree tree = new JTree(); // a sample tree
Object root = tree.getModel().getRoot(); // a DefaultMutableTreeNode
String json = objectMapper.writeValueAsString(root);
System.out.println(json);
DefaultMutableTreeNode root2 = objectMapper.readValue(json, DefaultMutableTreeNode.class);
它生成以下 JSON 輸出：
{
"allowsChildren" : true,
"userObject" : "JTree",
"children" : [ {
"allowsChildren" : true,
"userObject" : "colors",
"children" : [ {
"allowsChildren" : true,
"userObject" : "blue"
}, {
"allowsChildren" : true,
"userObject" : "violet"
}, {
"allowsChildren" : true,
"userObject" : "red"
}, {
"allowsChildren" : true,
"userObject" : "yellow"
} ]
}, {
"allowsChildren" : true,
"userObject" : "sports",
"children" : [ {
"allowsChildren" : true,
"userObject" : "basketball"
}, {
"allowsChildren" : true,
"userObject" : "soccer"
}, {
"allowsChildren" : true,
"userObject" : "football"
}, {
"allowsChildren" : true,
"userObject" : "hockey"
} ]
}, {
"allowsChildren" : true,
"userObject" : "food",
"children" : [ {
"allowsChildren" : true,
"userObject" : "hot dogs"
}, {
"allowsChildren" : true,
"userObject" : "pizza"
}, {
"allowsChildren" : true,
"userObject" : "ravioli"
}, {
"allowsChildren" : true,
"userObject" : "bananas"
} ]
} ]
}
下面DefaultMutableTreeNodeDeserializer負責將 JSON 轉換回DefaultMutableTreeNode.
這DefaultMutableTreeNode非常不像 POJO，因此不能與杰克遜一起很好地工作。因此，我創建了一個表現良好的POJO幫助器類（具有屬性 和） allowsChildren，并讓 Jackson 將 JSON 內容反序列化到該類中。然后我將對象（及其 子對象）轉換為對象（帶有子對象）。userObjectchildrenPOJOPOJODefaultMutableTreeNodeDefaultMutableTreeNode
public class DefaultMutableTreeNodeDeserializer extends JsonDeserializer<DefaultMutableTreeNode> {
@Override
public DefaultMutableTreeNode deserialize(JsonParser parser, DeserializationContext context)
throws IOException {
return parser.readValueAs(POJO.class).toDefaultMutableTreeNode();
}
private static class POJO {
private boolean allowsChildren;
private Object userObject;
private List<POJO> children;
// no need for: POJO parent
public DefaultMutableTreeNode toDefaultMutableTreeNode() {
DefaultMutableTreeNode node = new DefaultMutableTreeNode();
node.setAllowsChildren(allowsChildren);
node.setUserObject(userObject);
if (children != null) {
for (POJO child : children) {
node.add(child.toDefaultMutableTreeNode()); // recursion
// this did also set the parent of the child-node
}
}
return node;
}
// Following setters needed by Jackson's deserialization:
public void setAllowsChildren(boolean allowsChildren) {
this.allowsChildren = allowsChildren;
}
public void setUserObject(Object userObject) {
this.userObject = userObject;
}
public void setChildren(List<POJO> children) {
this.children = children;
}
}
}
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