通用列表上的 XStream 异常

Question

使用 XStream 1.4.4。

我有以下 XML：

<app name="MyApp">
    <properties>
        <property name="fizz" value="buzz" />
        <property name="foo" value="bar" />
    </properties>

    <fruit type="apple" />

    <!-- ...etc. -->
</app>

以及属性列表的相应 POJO，以及属性本身：

@XStreamAlias("properties")
public class Properties {
    private List<Property> properties = new ArrayList<Property>();

    public List<Property> getProperties() {
        return properties;
    }

    public void setProperties(List<Property> properties) {
        this.properties = properties;
    }
}

@XStreamAlias("property")
public class Property {
    private String name = null;

    private String value = null;

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getValue() {
        return value;
    }

    public void setValue(String value) {
        this.value = value;
    }
}

当我尝试运行以下代码时：

XStream xs = new XStream();
Strnig xml = getXML(); // Fetches the string of XML from above
App app = (App)xs.fromXML(xml);

我明白了：

Exception in thread "main" com.thoughtworks.xstream.converters.reflection.AbstractReflectionConverter$UnknownFieldException: No such field com.me.myapp.Properties.property
---- Debugging information ----
field               : property
class               : com.me.myapp.Properties
required-type       : com.me.myapp.Properties
converter-type      : com.thoughtworks.xstream.converters.reflection.ReflectionConverter
path                : /app/properties/property
line number         : 4
class[1]            : com.me.myapp.App
version             : null
-------------------------------
    at com.thoughtworks.xstream.converters.reflection.AbstractReflectionConverter.determineType(AbstractReflectionConverter.java:453)
    at com.thoughtworks.xstream.converters.reflection.AbstractReflectionConverter.doUnmarshal(AbstractReflectionConverter.java:294)
    ...rest of stack trace omitted for brevity

我哪里错了？

Answer 1

您根本不需要注释。只需使用别名 Property.class 作为“属性”，XStream 就会为您处理其他所有事情。

Answer 2

完全删除Properties 类。从 Property 类中删除 XStream 别名。将Property 类直接添加到App 类。使用以下别名以您希望的方式获得 XStream 序列化/反序列化：

xstream.alias("property", Property.class);
xstream.aliasField("property", Property.class, "properties");

应该这样做:-)

Answer 3

问题

• 你有一个类com.me.myapp.Properties，别名为properties
• 在其中，您有一个名为properties 的实例变量
• 这是properties的两个级别
• 您的 XML 有一级 properties

我的建议

• 在声明上方添加注释：

  @XStreamImplicit(itemFieldName="property")
  private List<Property> properties = new ArrayList<Property>()
  

• 这表示省略包装列表的元素<properties>（隐式列表），并且还为列表中的每个项目使用元素<property>。

测试：

• 一旦你认为你有正确的设置，首先通过生成 XML 进行测试：

  XStream xs = new XStream();
  App app = ...;              // Construct & populate a new App object
  String xml = xs.toXML(app); // Convert to XML
  System.out.println(xml);
  // This shows the XML format that must be used to parse XML to App.
  

Answer 4

此代码将 XML（由您提供）转换为 App 对象。由于您给定的代码不足，所以我将整个代码粘贴在这里。我想你忘了提xstream.processAnnotations(App.class);

<app name="MyApp">
    <properties>
        <property name="fizz" value="buzz" />
        <property name="foo" value="bar" />
    </properties>
</app>

类

package com.xstream;

import com.thoughtworks.xstream.annotations.XStreamAlias;

@XStreamAlias("app")
public class App {

  @XStreamAlias("properties")
  private Properties properties;

  /**
   * @param properties
   */
  public App(Properties properties) {
    super();
    this.properties = properties;
  }

  /**
   * 
   */
  public App() {
    super();
    // TODO Auto-generated constructor stub
  }

  /**
   * @return the properties
   */
  public Properties getProperties() {
    return properties;
  }

  /**
   * @param properties the properties to set
   */
  public void setProperties(Properties properties) {
    this.properties = properties;
  }

  /* (non-Javadoc)
   * @see java.lang.Object#toString()
   */
  @Override
  public String toString() {
    return "App [properties=" + properties + "]";
  }

}


----------

package com.xstream;                                                                                                   

import java.util.ArrayList;                                                                                            
import java.util.List;                                                                                                 

import com.thoughtworks.xstream.annotations.XStreamAlias;                                                              
import com.thoughtworks.xstream.annotations.XStreamImplicit;                                                           

@XStreamAlias("properties")                                                                                            
public class Properties {                                                                                              

    @XStreamImplicit(itemFieldName = "property")                                                                       
    private List<Property> property = new ArrayList<Property>();                                                       

    public List<Property> getProperties() {                                                                            
        return property;                                                                                               
    }                                                                                                                  

    public void setProperties(List<Property> properties) {                                                             
        this.property = properties;                                                                                    
    }                                                                                                                  

    /**                                                                                                                
     * @return the property                                                                                            
     */                                                                                                                
    public List<Property> getProperty() {                                                                              
      return property;                                                                                                 
    }                                                                                                                  

    /**                                                                                                                
     * @param property the property to set                                                                             
     */                                                                                                                
    public void setProperty(List<Property> property) {                                                                 
      this.property = property;                                                                                        
    }                                                                                                                  

    /* (non-Javadoc)                                                                                                   
     * @see java.lang.Object#toString()                                                                                
     */                                                                                                                
    @Override                                                                                                          
    public String toString() {                                                                                         
      return "Properties [property=" + property + "]";                                                                 
    }                                                                                                                  


}                                                                                                                      
----------------

package com.xstream;

import com.thoughtworks.xstream.annotations.XStreamAlias;
import com.thoughtworks.xstream.annotations.XStreamAsAttribute;

@XStreamAlias("property")
public class Property {

  @XStreamAsAttribute
    private String name = null;

  @XStreamAsAttribute
    private String value = null;

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getValue() {
        return value;
    }

    public void setValue(String value) {
        this.value = value;
    }

    /* (non-Javadoc)
     * @see java.lang.Object#toString()
     */
    @Override
    public String toString() {
      return "Property [name=" + name + ", value=" + value + "]";
    }


}

Main 类的代码是。

XStream xstream = new XStream();
xstream.processAnnotations(App.class);

App app = null;
try {
  app = (App) xstream.fromXML(new FileInputStream(new File("D:/property.xml")));
}
catch (FileNotFoundException e) {
  e.printStackTrace();
}

System.out.println(app.toString());