简述
将对象集合组合成树形结构，使客户端可以以一致的方式处理单个对象(叶子节点)和组合对象(根节点)
话不多说，上优化案例。
优化案例
最初版v0
不使用组合模式。
现有一个文件和目录的管理模块。如样例。
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| public class File {
private String path;
private Directory parent;
public File(Directory dir, String path) {
if (dir == null)
throw new RuntimeException("输入的dir不正确！");
if (path == null || path == "")
throw new RuntimeException("输入的path不正确！");
this.parent = dir;
this.path = dir.getPath() + path;
dir.add(this);
}
public String getPath() {
return this.path;
}
}
public class Directory {
private String path;
private List<Directory> dirs = new ArrayList<>();
private List<File> files = new ArrayList<>();
public Directory(String path) {
if (path == null || path == "")
throw new RuntimeException("输入的path不正确！");
this.path = path;
}
public Directory(Directory parent, String path) {
if (parent == null)
throw new RuntimeException("输入的parent不正确！");
if (path == null || path == "")
throw new RuntimeException("输入的path不正确！");
this.path = parent.getPath() + path;
parent.add(this);
}
public boolean add(File target) {
for (File file : files)
if (target.getPath().equals(file.getPath())) return false;
files.add(target);
return true;
}
public boolean add(Directory target) {
for (Directory dir : dirs)
if (target.getPath().equals(dir.getPath())) return false;
dirs.add(target);
return true;
}
public boolean remove(Directory target) {
for (Directory dir : dirs)
if (target.getPath().equals(dir.getPath())) {
dirs.remove(dir);
return true;
}
return false;
}
public boolean remove(File target) {
for (File file : files)
if (target.getPath().equals(file.getPath())) {
files.remove(file);
return true;
}
return false;
}
public String getPath() {
return this.path;
}
public List<Directory> getDirs() {
return this.dirs;
}
public List<File> getFiles() {
return this.files;
}
}
|
不使用组合模式，我们来看看客户端的使用。
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| public class Client {
public static void main(String[] args) {
Directory root = new Directory("/root");
Directory home = new Directory(root, "/home");
Directory user1 = new Directory(home, "/user1");
Directory text = new Directory(user1, "/text");
Directory image = new Directory(user1, "/image");
Directory png = new Directory(image, "/png");
Directory gif = new Directory(image, "/gif");
File f1 = new File(text, "/f1.txt");
File f2 = new File(text, "/f2.txt");
File f3 = new File(png, "/f3.png");
File f4 = new File(gif, "/f4.gif");
File f5 = new File(png, "/f5.png");
print(root);
}
public static void print(Directory root) {
System.out.println(root.getPath());
List<Directory> dirs = root.getDirs();
List<File> files = root.getFiles();
for (int i = 0; i < dirs.size(); i ++) {
print(dirs.get(i));
}
for (int i = 0; i < files.size(); i ++) {
System.out.println(files.get(i).getPath());
}
}
}
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可以看到print方法的实现比较复杂，因为File和Directory是完全不同类型，所以只能对其分别处理。
如何让客户端对于File和Directory采用一致的处理方式？用组合模式啊！！！
修改版v1(透明组合模式)
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| public interface Node {
boolean add(Node node);
boolean remove(Node node);
List<Node> getChildren();
String getPath();
}
public class File implements Node {
private String path;
private Node parent;
public File(Node parent, String path) {
if (parent == null)
throw new RuntimeException("输入的dir不正确！");
if (path == null || path == "")
throw new RuntimeException("输入的path不正确！");
this.parent = parent;
this.path = parent.getPath() + path;
parent.add(this);
}
public boolean add(Node node) {
throw new RuntimeException("不支持此方法!");
}
public boolean remove(Node node) {
throw new RuntimeException("不支持此方法!");
}
public List<Node> getChildren() {
throw new RuntimeException("不支持此方法!");
}
public String getPath() {
return this.path;
}
}
public class Directory implements Node {
private String path;
private List<Node> children = new ArrayList<>();
public Directory(String path) {
if (path == null || path == "")
throw new RuntimeException("输入的path不正确！");
this.path = path;
}
public Directory(Node parent, String path) {
if (parent == null)
throw new RuntimeException("输入的parent不正确！");
if (path == null || path == "")
throw new RuntimeException("输入的path不正确！");
this.path = parent.getPath() + path;
parent.add(this);
}
public boolean add(Node target) {
for (Node node : children)
if (target.getPath().equals(node.getPath())) return false;
children.add(target);
return true;
}
public boolean remove(Node target) {
for (Node node : children)
if (target.getPath().equals(node.getPath())) {
children.remove(node);
return true;
}
return false;
}
public String getPath() {
return this.path;
}
public List<Node> getChildren() {
return this.children;
}
}
|
通过在File和Directory的高层新增Node接口，面向接口编程加上File和Directory形成的树形结构使得客户端可以很自然地一致处理File和Directory。来看看客户端代码。
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| public class Client {
public static void main(String[] args) {
Node root = new Directory("/root");
Node home = new Directory(root, "/home");
Node user1 = new Directory(home, "/user1");
Node text = new Directory(user1, "/text");
Node image = new Directory(user1, "/image");
Node png = new Directory(image, "/png");
Node gif = new Directory(image, "/gif");
Node f1 = new File(text, "/f1.txt");
Node f2 = new File(text, "/f2.txt");
Node f3 = new File(png, "/f3.png");
Node f4 = new File(gif, "/f4.gif");
Node f5 = new File(png, "/f5.png");
print(root);
}
public static void print(Node root) {
System.out.println(root.getPath());
List<Node> nodes = root.getChildren();
for (int i = 0; i < nodes.size(); i ++) {
Node node = nodes.get(i);
if (node instanceof File) {
System.out.println(node.getPath());
continue;
}
print(node);
}
}
}
|
别高兴的太早了，虽然我们实现了最初的需求，但是有一处的代码不是很健康。在File中有三个方法实际上并没有被实现，有些臃肿。
修改版v2(安全组合模式)
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| public interface Node {
String getPath();
}
public class File implements Node {
private String path;
private Node parent;
public File(Directory parent, String path) {
if (parent == null)
throw new RuntimeException("输入的dir不正确！");
if (path == null || path == "")
throw new RuntimeException("输入的path不正确！");
this.parent = parent;
this.path = parent.getPath() + path;
parent.add(this);
}
public String getPath() {
return this.path;
}
}
public class Directory implements Node {
private String path;
private List<Node> children = new ArrayList<>();
public Directory(String path) {
if (path == null || path == "")
throw new RuntimeException("输入的path不正确！");
this.path = path;
}
public Directory(Directory parent, String path) {
if (parent == null)
throw new RuntimeException("输入的parent不正确！");
if (path == null || path == "")
throw new RuntimeException("输入的path不正确！");
this.path = parent.getPath() + path;
parent.add(this);
}
public boolean add(Node target) {
for (Node node : children)
if (target.getPath().equals(node.getPath())) return false;
children.add(target);
return true;
}
public boolean remove(Node target) {
for (Node node : children)
if (target.getPath().equals(node.getPath())) {
children.remove(node);
return true;
}
return false;
}
public String getPath() {
return this.path;
}
public List<Node> getChildren() {
return this.children;
}
}
|
修改Node接口的抽象方法后代码清爽了很多。客户端调用需要稍微修改下。
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| public class Client {
public static void main(String[] args) {
Directory root = new Directory("/root");
Directory home = new Directory(root, "/home");
Directory user1 = new Directory(home, "/user1");
Directory text = new Directory(user1, "/text");
Directory image = new Directory(user1, "/image");
Directory png = new Directory(image, "/png");
Directory gif = new Directory(image, "/gif");
File f1 = new File(text, "/f1.txt");
File f2 = new File(text, "/f2.txt");
File f3 = new File(png, "/f3.png");
File f4 = new File(gif, "/f4.gif");
File f5 = new File(png, "/f5.png");
print(root);
}
public static void print(Directory root) {
System.out.println(root.getPath());
List<Node> nodes = root.getChildren();
for (int i = 0; i < nodes.size(); i ++) {
Node node = nodes.get(i);
if (nodes.get(i) instanceof File) {
System.out.println(node.getPath());
continue;
}
print((Directory) node);
}
}
}
|
其实透明组合模式和安全组合模式看着用就好了，其实问题不大的。
总结
优点
- 让客户端可以一致地处理单一对象和组合对象。
缺点
- 局限性太强，只有可以构成树形结构的对象集合才可以使用。
适用场景
- 只有在对象集合可以组合成树形结构时才可以使用。
