使用 STAX 解析器将 XML 解组为三个不同对象的列表

Question

有没有一种方法可以让我使用 STAX 解析器有效地解析一个 XML 文档，其中包含多个不同 classes (POJO) 的对象列表。我的 XML 的确切结构如下（class 名字不是真实的）

<?xml version="1.0" encoding="utf-8"?>
<root>
    <notes />
    <category_alpha>
        <list_a>
            <class_a_object></class_a_object>
            <class_a_object></class_a_object>
            <class_a_object></class_a_object>
            <class_a_object></class_a_object>
            .
            .
            .
        </list_a>
        <list_b>
            <class_b_object></class_b_object>
            <class_b_object></class_b_object>
            <class_b_object></class_b_object>
            <class_b_object></class_b_object>
            .
            .
            .
        </list_b>
    </category_alpha>
    <category_beta>
        <class_c_object></class_c_object>
        <class_c_object></class_c_object>
        <class_c_object></class_c_object>
        <class_c_object></class_c_object>
        <class_c_object></class_c_object>
        .
        .
        .
        .
        .
    </category_beta>
</root>

我一直在使用 STAX 解析器，即 XStream 库，link：XStream

只要我的 XML 包含一个 class 个对象的列表，它就可以正常工作，但我不知道如何处理包含不同 XML 个对象列表的 XML =21=]es。

非常感谢任何帮助，如果我没有提供足够的信息或者我没有正确地表述问题，请告诉我。

Answer 1

我已经为提供的示例创建了一个解析器。 https://github.com/sbzDev/Whosebug/tree/master/question56087924

import com.thoughtworks.xstream.annotations.XStreamAlias;

import java.util.List;

@XStreamAlias("root")
public class Root {

    String notes;

    @XStreamAlias("category_alpha")
    CategoryAlpha categoryAlpha;


    @XStreamAlias("category_beta")
    List<C> listC;

    static class CategoryAlpha {

        @XStreamAlias("list_a")
        List<A> listA;

        @XStreamAlias("list_b")
        List<B> listB;
    }

    @XStreamAlias("class_a_object")
    static class A {
    }

    @XStreamAlias("class_b_object")
    static class B {
    }

    @XStreamAlias("class_c_object")
    static class C {
    }
}

解析器：

import com.thoughtworks.xstream.XStream;

public class SampleRootParser {

    public Root parse(String xmlContent){
        XStream xstream = new XStream();
        xstream.processAnnotations(Root.class);
        return  (Root)xstream.fromXML(xmlContent);
    }
}

也许您可以提供实际 XML 和预期结果？

Answer 2

您可以使用 Declarative Stream Mapping (DSM) 流解析库轻松将复杂的 XML 转换为 java class。它使用 StAX 来解析 XML.

我跳过获取 notes 标签并在 class_x_object 标签中添加一个字段以进行演示。

这里是 XML:

<?xml version="1.0" encoding="utf-8"?>
<root>
    <notes />
    <category_alpha>
        <list_a>
            <class_a_object>
                <fieldA>A1</fieldA>
            </class_a_object>
            <class_a_object>
                <fieldA>A2</fieldA>
            </class_a_object>
            <class_a_object>
                <fieldA>A3</fieldA>
            </class_a_object>

        </list_a>
        <list_b>
            <class_b_object>
                <fieldB>B1</fieldB>
            </class_b_object>
            <class_b_object>
                <fieldB>B2</fieldB>
            </class_b_object>
            <class_b_object>
                <fieldB>B3</fieldB>
            </class_b_object>
        </list_b>
    </category_alpha>
    <category_beta>
        <class_c_object>
          <fieldC>C1</fieldC>
        </class_c_object>
        <class_c_object>
          <fieldC>C2</fieldC>
        </class_c_object>
        <class_c_object>
          <fieldC>C3</fieldC>
        </class_c_object>
    </category_beta>
</root>

首先，您必须以 yaml 或 JSON 格式定义 XML 数据和 class 字段之间的映射。

以下是映射定义：

result:     
   type: object
   path: /root   
   fields:
     listOfA:
       type: array
       path: .*class_a_object  # path is regex
       fields:
          fieldOfA:
            path: fieldA
     listOfB:
       type: array
       path: .*class_b_object
       fields:
          fieldOfB:
            path: fieldB 
     listOfC:
       type: array
       path: .*class_c_object
       fields:
          fieldOfC:
            path: fieldC

Java class 您要反序列化：

public class Root {
    public List<A> listOfA;
    public List<B> listOfB;
    public List<C> listOfC;

    public static class A{
        public String fieldOfA;
    }
    public static class B{
        public String fieldOfB;
    }
    public static class C{
        public String fieldOfC;
    }

}

Java 要解析的代码 XML:

DSM dsm=new DSMBuilder(new File("path/to/mapping.yaml")).setType(DSMBuilder.TYPE.XML).create(Root.class);
Root root =  (Root)dsm.toObject(xmlFileContent);
// write root object as json
dsm.getObjectMapper().writerWithDefaultPrettyPrinter().writeValue(System.out, object);

这是输出：

{
  "listOfA" : [ {"fieldOfA" : "A1"}, {"fieldOfA" : "A2"}, {"fieldOfA" : "A3"} ],
  "listOfB" : [ {"fieldOfB" : "B1"}, {"fieldOfB" : "B2"}, "fieldOfB" : "B3"} ],
  "listOfC" : [ {"fieldOfC" : "C1"}, {"fieldOfC" : "C2"}, {"fieldOfC" : "C3"} ]
}

更新：

As I understand from your comment, you want to read big XML file as a stream. and process data while you are reading the file.

DSM 允许您在阅读时处理数据 XML。

声明三个不同的函数来处理部分数据。

FunctionExecutor processA=new FunctionExecutor(){
            @Override
            public void execute(Params params) {

                Root.A object=params.getCurrentNode().toObject(Root.A.class);

                // process aClass; save to db. call service etc.
            }
        };
FunctionExecutor processB=new FunctionExecutor(){
            @Override
            public void execute(Params params) {

                Root.B object=params.getCurrentNode().toObject(Root.B.class);

                // process aClass; save to db. call service etc.
            }
        };

FunctionExecutor processC=new FunctionExecutor(){
            @Override
            public void execute(Params params) {

                Root.C object=params.getCurrentNode().toObject(Root.C.class);

                // process aClass; save to db. call service etc.
            }
        };

将函数注册到 DSM

 DSMBuilder builder = new DSMBuilder(new File("path/to/mapping.yaml")).setType(DSMBuilder.TYPE.XML);

       // register function
        builder.registerFunction("processA",processA);
        builder.registerFunction("processB",processB);
        builder.registerFunction("processC",processC);

        DSM dsm= builder.create();
        Object object =  dsm.toObject(xmlContent);

更改映射文件以调用已注册的函数

result:     
   type: object
   path: /root   
   fields:
     listOfA:
       type: object
       function: processA  # when 'class_a_object' tag closed processA function will be executed.
       path: .*class_a_object  # path is regex
       fields:
          fieldOfA:
            path: fieldA
     listOfB:
       type: object
       path: .*class_b_object
       function: processB# register function
       fields:
          fieldOfB:
            path: fieldB 
     listOfC:
       type: object
       path: .*class_c_object
       function: processC# register function
       fields:
          fieldOfC:
            path: fieldC

Answer 3

您可以使用 Java Architecture for XML binding JAXB 和使用 POJO classes 的 Unmarshall，如下所述。

首先创建 POJO classes（我从您的 XML 文件中提取了几个节点并创建了 POJO。您可以对其余部分执行类似的操作）。下面是我考虑的XML

<?xml version="1.0" encoding="utf-8"?>
<root>
    <category_alpha>
        <list_a>
            <class_a_object></class_a_object>
            <class_a_object></class_a_object>
            <class_a_object></class_a_object>
            <class_a_object></class_a_object>
        </list_a>
        <list_b>
            <class_b_object></class_b_object>
            <class_b_object></class_b_object>
            <class_b_object></class_b_object>
            <class_b_object></class_b_object>
        </list_b>
    </category_alpha>
</root>

以下是根的 POJO classes，category_alpha、list_a、list_b、class_a_object 和 class_b_object

import java.util.List;

import javax.xml.bind.annotation.XmlAccessType;
import javax.xml.bind.annotation.XmlAccessorType;
import javax.xml.bind.annotation.XmlElement;
import javax.xml.bind.annotation.XmlRootElement;


@XmlRootElement(name = "root")
@XmlAccessorType (XmlAccessType.FIELD)
public class Root {

    @XmlElement(name = "category_alpha")
    private List<CategoryAlpha> categoryAlphaList = null;

    public List<CategoryAlpha> getCategoryAlphaList() {
        return categoryAlphaList;
    }

    public void setCategoryAlphaList(List<CategoryAlpha> categoryAlphaList) {
        this.categoryAlphaList = categoryAlphaList;
    }
}

在下面 classes.class 中导入与上述 class 相似的 java 导入。

@XmlRootElement(name = "category_alpha")
@XmlAccessorType (XmlAccessType.FIELD)
public class CategoryAlpha {

    @XmlElement(name = "list_a")
    private List<ListAClass> list_a_collectionlist = null;

    @XmlElement(name = "list_b")
    private List<ListBClass> list_b_collectionlist = null;


    public List<ListAClass> getList_a_collectionlist() {
        return list_a_collectionlist;
    }


    public void setList_a_collectionlist(List<ListAClass> list_a_collectionlist) {
        this.list_a_collectionlist = list_a_collectionlist;
    }


    public List<ListBClass> getList_b_collectionlist() {
        return list_b_collectionlist;
    }


    public void setList_b_collectionlist(List<ListBClass> list_b_collectionlist) {
        this.list_b_collectionlist = list_b_collectionlist;
    }
}

@XmlRootElement(name = "list_a")
@XmlAccessorType (XmlAccessType.FIELD)
public class ListAClass {

    @XmlElement(name = "class_a_object")
    private List<ClassAObject> classAObjectList = null;

    public List<ClassAObject> getClassAObjectList() {
        return classAObjectList;
    }

    public void setClassAObjectList(List<ClassAObject> classAObjectList) {
        this.classAObjectList = classAObjectList;
    }
}

@XmlRootElement(name = "list_b")
@XmlAccessorType (XmlAccessType.FIELD)
public class ListBClass {

    @XmlElement(name = "class_b_object")
    private List<ClassBObject> classBObjectList = null;

    public List<ClassBObject> getClassBObjectList() {
        return classBObjectList;
    }

    public void setClassBObjectList(List<ClassBObject> classBObjectList) {
        this.classBObjectList = classBObjectList;
    }
}

@XmlRootElement(name = "class_a_object")
@XmlAccessorType (XmlAccessType.FIELD)
public class ClassAObject {

}

@XmlRootElement(name = "class_b_object")
@XmlAccessorType (XmlAccessType.FIELD)
public class ClassBObject {

}

这是主要内容class

import java.io.File;

import javax.xml.bind.JAXBContext;
import javax.xml.bind.JAXBException;
import javax.xml.bind.Unmarshaller;

public class UnmarshallMainClass {

    public static void main(String[] args) throws JAXBException {
        JAXBContext jaxbContext = JAXBContext.newInstance(Root.class);
        Unmarshaller jaxbUnmarshaller = jaxbContext.createUnmarshaller();

        // This root object contains all the list of objects you are looking for
        Root emps = (Root) jaxbUnmarshaller.unmarshal( new File("sample.xml") );
    }

}

通过使用根对象和其他对象中的 getter，您可以检索根内所有对象的列表，如下所示。

List<CategoryAlpha> categoryAlphaList = emps.getCategoryAlphaList();

使用 STAX 解析器将 XML 解组为三个不同对象的列表

Unmarshalling XML to three lists of different objects using STAX Parser

java

xml

xml-parsing

jaxb

stax