不用递归实现生成树的Example

这是用于生成树的类,适用于分类号采用的是自增的方式，并且List中的元素是按从小到大的顺序进行过排序的（这个在查询时很容易实现，加上order by [id] 即可）。
这样只需要进行一次数据库查询操作，如果用递归会查询N多次。

package com.zhenjw.tree;

import java.util.List;
import java.util.Vector;

public class Tree {

    public static List createTree(List<TreeNode> all) {

	if (all == null || all.size() == 0)
	    return null;

	int count = all.size();
	TreeNode bi = new TreeNode();
	TreeNode bj = new TreeNode();

	//先组织好父子之间的关系然后 填充layer与parentname这两个字段的内容

	//1、组织好父子之间的关系
	for (int i = 0; i < count; i++) {
	    bi = (TreeNode) all.get(i);
	    bi.setLayer(0);
	    bi.setFullName(bi.getName());
	    boolean trans = false;
	    for (int j = i + 1; j < count; j++) {
		bj = (TreeNode) all.get(j);
		if (bi.getParentNo() == bj.getNo()) {
		    //是父子关系 
		    all.set(i, bj);
		    all.set(j, bi); //父在前面子在后面					
		    trans = true;
		}
	    }
	    if (trans)
		i--;
	}

	//2、组织各个元素所在的层以及全称
	for (int i = 0; i < count; i++) {
	    bi = (TreeNode) all.get(i);
	    for (int j = i + 1; j < count; j++) {
		bj = (TreeNode) all.get(j);
		if (bj.getParentNo() == bi.getNo()) {
		    bj.setLayer(bi.getLayer() + 1);
		    bj.setFullName(bi.getFullName() + "&gt;&gt;" + bj.getName());
		}
	    }
	}

	return all;
    }

    public static List createTree(List all, int topid) {
	all = createTree(all);
	int count = all.size();
	TreeNode bj = new TreeNode();

	//把不在这一顶层的其它项都删除掉
	int topidj = 0;
	int topidlayer = 0;

	//查找ID=topid所在的位置
	for (int j = 0; j < count; j++) {
	    bj = (TreeNode) all.get(j);
	    //找到TopID对应的对象
	    if (bj.getNo() == topid) {
		topidj = j;
		topidlayer = bj.getLayer();
		break;
	    }
	}
	List reslut = new Vector();
	for (int j = topidj; j < count; j++) {
	    bj = (TreeNode) all.get(j);
	    //找到TopID对应的对象
	    if (bj.getLayer() <= topidlayer && j > topidj) {
		break;
	    } else {
		bj.setLayer(bj.getLayer() - topidlayer);
		reslut.add(bj);
	    }
	}
	return reslut;
    }

}



package com.zhenjw.tree;

import org.apache.commons.lang.builder.ToStringBuilder;

public class TreeNode<T> {

    private long no;

    private long parentNo;

    private String name;

    private String fullName;

    private int layer;

    //用于保存原始的对象，方便在列表时得到对象的其它的信息
    private T entity;

    public T getEntity() {
	return entity;
    }

    public void setEntity(T entity) {
	this.entity = entity;
    }

    public String getFullName() {
	return fullName;
    }

    public void setFullName(String fullName) {
	this.fullName = fullName;
    }

    public String getName() {
	return name;
    }

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

    public long getNo() {
	return no;
    }

    public void setNo(long no) {
	this.no = no;
    }

    public long getParentNo() {
	return parentNo;
    }

    public void setParentNo(long parentNo) {
	this.parentNo = parentNo;
    }

    public TreeNode(long no, long parentNo, String name, String fullName, int layer, T entity) {
	super();
	this.no = no;
	this.parentNo = parentNo;
	this.name = name;
	this.fullName = fullName;
	this.layer = layer;
	this.entity = entity;
    }
    
    

    public TreeNode(long no, long parentNo, String name, T entity) {
	super();
	this.no = no;
	this.parentNo = parentNo;
	this.name = name;
	this.entity = entity;
    }

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

    public int getLayer() {
	return layer;
    }

    public void setLayer(int layer) {
	this.layer = layer;
    }

    public String toString() {

	return ToStringBuilder.reflectionToString(this);

    }
}