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。