Gson 转换树型结构的实例

• 构建树型结构的实体
  树型结构的实体主要是用组合模式构建的，且是透明模式的组合模式；关于组合模式，此处不再赘述。
  代码部分：

> package com.dp.composite.example4;

        import com.google.gson.annotations.Expose;

        import java.io.Serializable;
        import java.util.ArrayList;

/**
 * @desc 抽象的缺省类
 * @creator caozhiqing
 * @data 2015/8/12
 */
public abstract class Component implements Serializable{


    private transient Component parent;

    public Component getParent() {
        return parent;
    }

    public void setParent(Component parent) {
        this.parent = parent;
    }

    public void addChild(Component component){
        throw new UnsupportedOperationException("不支持此方法");
    }

    public void getChild(int index) {
        throw new UnsupportedOperationException("不支持此方法");
    }

    public ArrayList<Component> getChild() {
        throw new UnsupportedOperationException("不支持此方法");
    }

    public void removeChile(Component component) {
        throw new UnsupportedOperationException("不支持此方法");
    }

    public abstract void operation(String pre);
}

package com.dp.composite.example4;

import java.util.ArrayList;
import java.util.Iterator;

/**
 * @desc 具体树枝类，即容器类
 * @creator caozhiqing
 * @data 2015/8/12
 */
public class Composite extends Component {

    ArrayList<Component> children ;

    private String name;
    public Composite(String name){
        this.name= name;
    }

    @Override
    public void addChild(Component component) {
        if(component == null){
            return;
        }
        if(children == null){
            children = new ArrayList<Component>();
        }
        children.add(component);
        component.setParent(this);
    }

    @Override
    public void removeChile(Component component) {
        if(component == null || children == null){
            return;
        }
        Iterator<Component> iterator = children.iterator();
        while (iterator.hasNext()){
            Component component1 = iterator.next();
            if(component1 != null && component1 == component){
                iterator.remove();
                if(component instanceof Composite && component1.getChild() != null){
                    for(Component component2:component.getChild()){
                        component2.setParent(this);
                        addChild(component2);
                    }
                }
                break;
            }
        }
    }

    @Override
    public ArrayList<Component> getChild() {
        return children;
    }

    @Override
    public void operation(String pre) {
        System.out.println(pre+"#"+this.name);
        pre +="   ";
        if(children != null && children.size()>0){
            for(Component component:children){
                component.operation(pre);
            }
        }
    }
}

package com.dp.composite.example4;

/**
 * @desc 叶子类，即没有子节点
 * @creator caozhiqing
 * @data 2015/8/12
 */
public class Leaf extends Component {

    private String name;
    public Leaf(String name){
        this.name = name;
    }

    @Override
    public void operation(String pre) {

        System.out.println(pre+"-"+this.name);
    }
}

package com.dp.composite.example4;

import com.google.gson.Gson;

/**
* @desc 客户端
* @creator caozhiqing
* @data 2015/8/12
*/
public class Client {
public static void main(String[] arg){
Component root = new Composite(“服装”);
Component man = new Composite(“男装”);
Component wom = new Composite(“女装”);

    root.addChild(man);
    root.addChild(wom);

    Component leaf1 = new Leaf("夹克");
    Component leaf2 = new Leaf("寸衫");
    man.addChild(leaf1);
    man.addChild(leaf2);

    Component leaf3 = new Leaf("短裙");
    Component leaf4 = new Leaf("Browse");
    wom.addChild(leaf3);
    wom.addChild(leaf4);
    root.operation("");

    System.out.println("----------->");

// root.removeChile(man);
// root.operation(“”);
Gson gson = new Gson();
System.out.println(gson.toJson(root));
}

}
“`

• 解析
  此处最主要的是忽略每个子节点的父节点。
  
  即在Component 中把此属性设置为transient 即不被序列化，且不能使用Gson提供的@Expose(serialize = false) 或@Expose（与new GsonBuilder().excludeFieldsWithoutExposeAnnotation().create() ）配合使用。

• JSON 结果。

{“children”:[{“children”:[{“name”:”夹克”},{“name”:”寸衫”}],”name”:”男装”},{“children”:[{“name”:”短裙”},{“name”:”Browse”}],”name”:”女装”}],”name”:”服装”}
- 总结：
如果古加入transient关键字，会报栈溢出的bug
这回crm系统封装解析json和以树型为结构的json解析很有帮助。