又称“整体—部分”模式，组合多个对象形成树形结构以表示具有“整体—部分”关系的层次结构，使用户对单个对象和组合对象具有访问一致性。

角色

抽象构件（Component）：抽象类，定义叶子构件和树枝构件的公共接口，可提供默认实现，叶子构件中提供空实现或抛出异常
叶子构件（Leaf）：没有子节点，实现抽象构件中的公共接口（空实现或抛出异常）
树枝构件（Composite）：包含子节点，子节点可以是叶子构件也可以是树枝构件，实现抽象构件中公共接口

抽象构件 Component

public abstract class Component {protected static final String SPACE = " ";protected static final String hyphen = "-";private String name;public Component(String name) {this.name = name;}public String getName() {return this.name;}public abstract boolean add(Component component);public abstract Component getChild(int index);public abstract boolean remove(Component c);public abstract void operation(int spaces);
}

叶子构件 Leaf

import java.util.Collections;public class Leaf extends Component {public Leaf(String name) {super(name);}@Overridepublic boolean add(Component component) {throw new UnsupportedOperationException(getClass().getSimpleName());}@Overridepublic Component getChild(int index) {throw new UnsupportedOperationException(getClass().getSimpleName());}@Overridepublic boolean remove(Component c) {throw new UnsupportedOperationException(getClass().getSimpleName());}@Overridepublic void operation(int spaces) {StringBuffer line = new StringBuffer();if (spaces > 0) {line.append(String.join("", Collections.nCopies(spaces, SPACE)));line.append("|- ");}line.append(getName());System.out.println(line);}
}

树枝构件 Composite

import java.util.ArrayList;
import java.util.Collections;
import java.util.List;public class Composite extends Component {private List<Component> components = new ArrayList<Component>();public Composite(String name) {super(name);}@Overridepublic boolean add(Component component) {return components.add(component);}@Overridepublic Component getChild(int index) {return components.get(index);}@Overridepublic boolean remove(Component c) {return components.remove(c);}@Overridepublic void operation(int spaces) {StringBuffer line = new StringBuffer();if (spaces > 0) {line.append(String.join("", Collections.nCopies(spaces, SPACE)));line.append("|- ");}line.append(getName());System.out.println(line);int length = line.length() - spaces;for (Component component : components) {int mid = (length % 2 == 0) ? (length / 2 - 1) : (length / 2 + 1);component.operation(mid + spaces);}}
}

测试类

public class CompositeTester {public static void main(String args[]) {Component root = new Composite("root");root.add(new Leaf("node#1"));Component branch2 = new Composite("branch#2");root.add(branch2);root.add(new Leaf("node#2"));branch2.add(new Leaf("node#3"));branch2.add(new Leaf("node#4"));Composite branch3 = new Composite("branch#3");branch2.add(branch3);branch3.add(new Leaf("node#5"));branch3.add(new Leaf("node#6"));branch3.add(new Leaf("node#7"));root.operation(0);Component leaf = new Leaf("node#8");leaf.add(new Leaf("node#9"));}
}

输出

root|- node#1|- branch#2|- node#3|- node#4|- branch#3|- node#5|- node#6|- node#7|- node#2
Exception in thread "main" java.lang.UnsupportedOperationException: Leafat com.designpatterns.composite.base.Leaf.add(Leaf.java:12)at com.designpatterns.composite.base.CompositeTester.main(CompositeTester.java:23)

举例：文件 & 文件夹

抽象构件 File

import lombok.Getter;
import lombok.Setter;import java.util.List;public abstract class File {@Getter @Setterprivate String pathname;@Getter @Setterprivate String path;@Getter @Setterprivate String fileName;public File(String pathname) {if (pathname == null) {throw new IllegalArgumentException(pathname);}pathname = pathname.replace("/", java.io.File.separator);if (!pathname.contains(java.io.File.separator)) {throw new IllegalArgumentException(pathname);}this.pathname = pathname;int indexOfSep = pathname.lastIndexOf(java.io.File.separator);this.path = pathname.substring(0, indexOfSep);this.fileName = pathname.substring(indexOfSep + 1);}public File(File parent, String fileName) {if (parent == null) {throw new IllegalArgumentException("null");}if (fileName == null || fileName.isEmpty()) {throw new IllegalArgumentException(fileName);}this.path = parent.getPathname();this.fileName = fileName;this.pathname = parent.getPathname() + java.io.File.separator + fileName;}public static boolean isDirectory(String fileName) {return !fileName.contains(".");}public abstract boolean add(File f);public abstract File getChild(String fileName);public abstract boolean remove(String fileName);public abstract List<String> list();
}

叶子构件 Text

import java.util.List;public class Text extends File {public Text(String pathname) {super(pathname);}public Text(File parent, String fileName) {super(parent, fileName);}@Overridepublic boolean add(File f) {throw new UnsupportedOperationException(getClass().getSimpleName());}@Overridepublic File getChild(String fileName) {throw new UnsupportedOperationException(getClass().getSimpleName());}@Overridepublic boolean remove(String fileName) {throw new UnsupportedOperationException(getClass().getSimpleName());}@Overridepublic List<String> list() {throw new UnsupportedOperationException(getClass().getSimpleName());}
}

叶子构件 Audio

import java.util.List;public class Audio extends File {public Audio(String pathname) {super(pathname);}public Audio(File parent, String fileName) {super(parent, fileName);}@Overridepublic boolean add(File f) {throw new UnsupportedOperationException(getClass().getSimpleName());}@Overridepublic File getChild(String fileName) {throw new UnsupportedOperationException(getClass().getSimpleName());}@Overridepublic boolean remove(String fileName) {throw new UnsupportedOperationException(getClass().getSimpleName());}@Overridepublic List<String> list() {throw new UnsupportedOperationException(getClass().getSimpleName());}
}

叶子构件 Video

import java.util.List;public class Video extends File {public Video(String pathname) {super(pathname);}public Video(File parent, String fileName) {super(parent, fileName);}@Overridepublic boolean add(File f) {throw new UnsupportedOperationException(getClass().getSimpleName());}@Overridepublic File getChild(String fileName) {throw new UnsupportedOperationException(getClass().getSimpleName());}@Overridepublic boolean remove(String fileName) {throw new UnsupportedOperationException(getClass().getSimpleName());}@Overridepublic List<String> list() {throw new UnsupportedOperationException(getClass().getSimpleName());}
}

树枝构件 Directory

import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;public class Directory extends File {private List<File> files = new ArrayList<>();public Directory(String pathname) {super(pathname);}public Directory(File parent, String fileName) {super(parent, fileName);}@Overridepublic boolean add(File f) {return files.add(f);}@Overridepublic File getChild(String fileName) {Iterator<File> iter = files.iterator();while (iter.hasNext()) {File f = iter.next();if (f.getFileName().equals(fileName)) {return f;}}return null;}@Overridepublic boolean remove(String fileName) {Iterator<File> iter = files.iterator();while (iter.hasNext()) {File f = iter.next();if (f.getFileName().equals(fileName)) {iter.remove();return true;}}return false;}@Overridepublic List<String> list() {List<String> pathnames = new ArrayList<>();for (File f : files) {pathnames.add(f.getPathname());if (isDirectory(f.getFileName())) {pathnames.addAll(f.list());}}return pathnames;}
}

测试类

import java.util.List;public class FileTester {public static void main(String args[]) {File root = new Directory("D:/root");File readme = new Text(root, "readme.txt");root.add(readme);File musicListTxt = new Text(root, "music-list.txt");root.add(musicListTxt);File musicDir = new Directory(root, "musics");File giveMeYourHeart = new Audio(musicDir, "give you my heart.mp3");File heyJude = new Audio(musicDir, "hey judy.wma");musicDir.add(giveMeYourHeart);musicDir.add(heyJude);root.add(musicDir);File videoListTxt = new Text(root, "video-list.txt");root.add(videoListTxt);File videoDir = new Directory(root, "videos");File superMan = new Video(videoDir, "超人.rmvb");videoDir.add(superMan);root.add(videoDir);List<String> pathnames = root.list();for (String pathname : pathnames) {System.out.println(pathname);}File file = root.getChild("readme.txt");System.out.println(file.getPathname());}
}

D:\root\readme.txt
D:\root\music-list.txt
D:\root\musics
D:\root\musics\give you my heart.mp3
D:\root\musics\hey judy.wma
D:\root\video-list.txt
D:\root\videos
D:\root\videos\超人.rmvb
D:\root\readme.txt

举例2：html元素

import lombok.Data;
import lombok.Getter;
import lombok.Setter;import java.util.HashMap;
import java.util.Map;public abstract class Element {@Getterprivate String tagName;protected long height;protected long lineHeight;protected long width;protected Margin margin = new Margin();private Border border = new Border();protected Padding padding = new Padding();protected Map<String, Object> styleCache = new HashMap<>();@Getter @Setterprivate String id;public Element(String tagName) {this.tagName = tagName;}public Element(String tagName, String id) {this.tagName = tagName;this.id = id;}public abstract boolean add(Element e);public abstract Element getChild(String id);public abstract boolean remove(Element e);public abstract boolean empty();public abstract void print(int tabs);public void addStyle(String name, Object value) {this.styleCache.put(name, value);}public void removeStyle(String name) {this.styleCache.remove(name);}public void setBorderTop(long top) {this.border.setTop(top);this.styleCache.put("border-top", top);}public void setBorderRight(long right) {this.border.setRight(right);this.styleCache.put("border-right", right);}public void setBorderBottom(long bottom) {this.border.setBottom(bottom);this.styleCache.put("border-bottom", bottom);}public void setBorderLeft(long left) {this.border.setLeft(left);this.styleCache.put("border-left", left);}public void setBorder(long topAndBottom, long leftAndRight) {this.border.setTop(topAndBottom);this.border.setRight(leftAndRight);this.border.setBottom(topAndBottom);this.border.setLeft(leftAndRight);this.styleCache.put("border-top", topAndBottom);this.styleCache.put("border-right", leftAndRight);this.styleCache.put("border-bottom", topAndBottom);this.styleCache.put("border-left", leftAndRight);}public void setBorder(long top, long right, long bottom, long left) {this.border.setTop(top);this.border.setRight(right);this.border.setBottom(bottom);this.border.setLeft(left);this.styleCache.put("border-top", top);this.styleCache.put("border-right", right);this.styleCache.put("border-bottom", bottom);this.styleCache.put("border-left", left);}public void setMarginTop(long top) {throw new UnsupportedOperationException(getClass().getSimpleName());}public void setMarginRight(long right) {throw new UnsupportedOperationException(getClass().getSimpleName());}public void setMarginBottom(long bottom) {throw new UnsupportedOperationException(getClass().getSimpleName());}public void setMarginLeft(long left) {throw new UnsupportedOperationException(getClass().getSimpleName());}public void setMargin(long topAndBottom, long leftAndRight) {throw new UnsupportedOperationException(getClass().getSimpleName());}public void setMargin(long top, long right, long bottom, long left) {throw new UnsupportedOperationException(getClass().getSimpleName());}public void setPaddingTop(long top) {throw new UnsupportedOperationException(getClass().getSimpleName());}public void setPaddingRight(long right) {throw new UnsupportedOperationException(getClass().getSimpleName());}public void setPaddingBottom(long bottom) {throw new UnsupportedOperationException(getClass().getSimpleName());}public void setPaddingLeft(long left) {throw new UnsupportedOperationException(getClass().getSimpleName());}public void setPadding(long topAndBottom, long leftAndRight) {throw new UnsupportedOperationException(getClass().getSimpleName());}public void setPadding(long top, long right, long bottom, long left) {throw new UnsupportedOperationException(getClass().getSimpleName());}@Datapublic class Margin {private long top;private long left;private long right;private long bottom;}@Datapublic class Border {private long top;private long left;private long right;private long bottom;}@Datapublic class Padding {private long top;private long left;private long right;private long bottom;}
}

import java.util.Collections;
import java.util.Map;public class InlineElement extends Element {private String text;public InlineElement(String tagName) {super(tagName);addStyle("display", "inline");}public InlineElement(String tagName, String id) {super(tagName, id);addStyle("display", "inline");}public String getText() {return text;}public void setText(String text) {this.text = text;}@Overridepublic boolean add(Element e) {throw new UnsupportedOperationException(getClass().getSimpleName());}@Overridepublic Element getChild(String id) {throw new UnsupportedOperationException(getClass().getSimpleName());}@Overridepublic boolean remove(Element e) {throw new UnsupportedOperationException(getClass().getSimpleName());}@Overridepublic boolean empty() {text = "";return true;}@Overridepublic void print(int tabs) {String prefix = String.join("", Collections.nCopies(tabs, "\t"));StringBuffer styles = new StringBuffer();for (Map.Entry<String, Object> style : styleCache.entrySet()) {if (styles.length() > 0) {styles.append(";");}styles.append(style.getKey()).append(":").append(style.getValue());}StringBuffer content = new StringBuffer();content.append(prefix).append("<").append(getTagName());if (getId() != null && !getId().isEmpty()) {content.append(" id=\"").append(getId());}content.append("\" style=\"").append(styles).append("\">");if (text != null && !text.isEmpty()) {content.append(text);}content.append("</").append(getTagName()).append(">");System.out.println(content);}
}

import java.util.Collections;
import java.util.Map;public class InlineBlockElement extends Element {private String text;public InlineBlockElement(String tagName) {super(tagName);addStyle("display", "inline-block");addStyle("float", "left");// or rightaddStyle("position", "absolute");// or fixed}public InlineBlockElement(String tagName, String id) {super(tagName, id);addStyle("display", "inline-block");addStyle("float", "left");// or rightaddStyle("position", "absolute");// or fixed}public String getText() {return text;}public void setText(String text) {this.text = text;}@Overridepublic boolean add(Element e) {throw new UnsupportedOperationException(getClass().getSimpleName());}@Overridepublic Element getChild(String id) {throw new UnsupportedOperationException(getClass().getSimpleName());}@Overridepublic boolean remove(Element e) {throw new UnsupportedOperationException(getClass().getSimpleName());}@Overridepublic boolean empty() {text = "";return true;}@Overridepublic void print(int tabs) {String prefix = String.join("", Collections.nCopies(tabs, "\t"));StringBuffer styles = new StringBuffer();for (Map.Entry<String, Object> style : styleCache.entrySet()) {if (styles.length() > 0) {styles.append(";");}styles.append(style.getKey()).append(":").append(style.getValue());}StringBuffer content = new StringBuffer();content.append(prefix).append("<").append(getTagName());if (getId() != null && !getId().isEmpty()) {content.append(" id=\"").append(getId());}content.append("\" style=\"").append(styles).append("\">");if (text != null && !text.isEmpty()) {content.append(text);}content.append(prefix).append("</").append(getTagName()).append(">");System.out.println(content);}public void setMarginTop(long top) {this.margin.setTop(top);this.styleCache.put("margin-top", top);}public void setMarginRight(long right) {this.margin.setRight(right);this.styleCache.put("margin-right", right);}public void setMarginBottom(long bottom) {this.margin.setBottom(bottom);this.styleCache.put("margin-bottom", bottom);}public void setMarginLeft(long left) {this.margin.setLeft(left);this.styleCache.put("margin-left", left);}public void setMargin(long topAndBottom, long leftAndRight) {this.margin.setTop(topAndBottom);this.margin.setRight(leftAndRight);this.margin.setBottom(topAndBottom);this.margin.setLeft(leftAndRight);this.styleCache.put("margin-top", topAndBottom);this.styleCache.put("margin-right", leftAndRight);this.styleCache.put("margin-bottom", topAndBottom);this.styleCache.put("margin-left", leftAndRight);}public void setMargin(long top, long right, long bottom, long left) {this.margin.setTop(top);this.margin.setRight(right);this.margin.setBottom(bottom);this.margin.setLeft(left);this.styleCache.put("margin-top", top);this.styleCache.put("margin-right", right);this.styleCache.put("margin-bottom", bottom);this.styleCache.put("margin-left", right);}public void setPaddingTop(long top) {this.padding.setTop(top);this.styleCache.put("padding-top", top);}public void setPaddingRight(long right) {this.padding.setRight(right);this.styleCache.put("padding-right", right);}public void setPaddingBottom(long bottom) {this.padding.setBottom(bottom);this.styleCache.put("padding-bottom", bottom);}public void setPaddingLeft(long left) {this.padding.setLeft(left);this.styleCache.put("padding-left", left);}public void setPadding(long topAndBottom, long leftAndRight) {this.padding.setTop(topAndBottom);this.padding.setRight(leftAndRight);this.padding.setBottom(topAndBottom);this.padding.setLeft(leftAndRight);this.styleCache.put("padding-top", topAndBottom);this.styleCache.put("padding-right", leftAndRight);this.styleCache.put("padding-bottom", topAndBottom);this.styleCache.put("padding-left", leftAndRight);}public void setPadding(long top, long right, long bottom, long left) {this.padding.setTop(top);this.padding.setRight(right);this.padding.setBottom(bottom);this.padding.setLeft(left);this.styleCache.put("padding-top", top);this.styleCache.put("padding-right", right);this.styleCache.put("padding-bottom", bottom);this.styleCache.put("padding-left", left);}
}

import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import java.util.Map;public class BlockElement extends Element {private String text;private Element parent;private List<Element> children = new ArrayList<>();public BlockElement(String tagName) {super(tagName);addStyle("display", "block");}public BlockElement(String tagName, String id) {super(tagName, id);addStyle("display", "block");}public String getText() {return text;}public void setText(String text) {this.text = text;}public long getHeight() {return this.height;}public void setHeight(long height) {this.height = height;this.styleCache.put("height", height);}public long getLineHeight() {return this.lineHeight;}public void setLineHeight(long lineHeight) {this.lineHeight = lineHeight;this.styleCache.put("line-height", lineHeight);}public long getWidth() {return this.width;}public void setWidth(long width) {this.width = width;this.styleCache.put("width", width);}@Overridepublic boolean add(Element e) {return children.add(e);}@Overridepublic Element getChild(String id) {for (Element child : children) {if (child.getId().equals(id)) {return child;}}return null;}@Overridepublic boolean remove(Element e) {return children.remove(e);}@Overridepublic boolean empty() {children.clear();return true;}@Overridepublic void print(int tabs) {StringBuffer styles = new StringBuffer();for (Map.Entry<String, Object> style : styleCache.entrySet()) {if (styles.length() > 0) {styles.append(";");}styles.append(style.getKey()).append(":").append(style.getValue());}String prefix = String.join("", Collections.nCopies(tabs, "\t"));StringBuffer startTag = new StringBuffer();startTag.append(prefix).append("<").append(getTagName());if (getId() != null && !getId().isEmpty()) {startTag.append(" id=\"").append(getId());}startTag.append("\" style=\"").append(styles).append("\">" );System.out.println(startTag);for (Element child : children) {child.print(tabs + 1);}System.out.println(prefix + "</" + getTagName() + ">");}public void setMarginTop(long top) {this.margin.setTop(top);this.styleCache.put("margin-top", top);}public void setMarginRight(long right) {this.margin.setRight(right);this.styleCache.put("margin-right", right);}public void setMarginBottom(long bottom) {this.margin.setBottom(bottom);this.styleCache.put("margin-bottom", bottom);}public void setMarginLeft(long left) {this.margin.setLeft(left);this.styleCache.put("margin-left", left);}public void setMargin(long topAndBottom, long leftAndRight) {this.margin.setTop(topAndBottom);this.margin.setRight(leftAndRight);this.margin.setBottom(topAndBottom);this.margin.setLeft(leftAndRight);this.styleCache.put("margin-top", topAndBottom);this.styleCache.put("margin-right", leftAndRight);this.styleCache.put("margin-bottom", topAndBottom);this.styleCache.put("margin-left", leftAndRight);}public void setMargin(long top, long right, long bottom, long left) {this.margin.setTop(top);this.margin.setRight(right);this.margin.setBottom(bottom);this.margin.setLeft(left);this.styleCache.put("margin-top", top);this.styleCache.put("margin-right", right);this.styleCache.put("margin-bottom", bottom);this.styleCache.put("margin-left", right);}public void setPaddingTop(long top) {this.padding.setTop(top);this.styleCache.put("padding-top", top);}public void setPaddingRight(long right) {this.padding.setRight(right);this.styleCache.put("padding-right", right);}public void setPaddingBottom(long bottom) {this.padding.setBottom(bottom);this.styleCache.put("padding-bottom", bottom);}public void setPaddingLeft(long left) {this.padding.setLeft(left);this.styleCache.put("padding-left", left);}public void setPadding(long topAndBottom, long leftAndRight) {this.padding.setTop(topAndBottom);this.padding.setRight(leftAndRight);this.padding.setBottom(topAndBottom);this.padding.setLeft(leftAndRight);this.styleCache.put("padding-top", topAndBottom);this.styleCache.put("padding-right", leftAndRight);this.styleCache.put("padding-bottom", topAndBottom);this.styleCache.put("padding-left", leftAndRight);}public void setPadding(long top, long right, long bottom, long left) {this.padding.setTop(top);this.padding.setRight(right);this.padding.setBottom(bottom);this.padding.setLeft(left);this.styleCache.put("padding-top", top);this.styleCache.put("padding-right", right);this.styleCache.put("padding-bottom", bottom);this.styleCache.put("padding-left", left);}
}

public class ElementTester {public static void main(String args[]) {Element div = new BlockElement("div", "content");InlineElement span = new InlineElement("span", "title");span.setText("设计模式之组合模式");Element a = new InlineElement("a", "goBaidu");Element input = new InlineBlockElement("input", "clickMe");Element content = new BlockElement("div", "description");Element ul = new BlockElement("ul", "ul");BlockElement li1 = new BlockElement("li", "li-1");li1.setText("1. 通过 a 标签跳到百度首页");BlockElement li2 = new BlockElement("li", "li-2");li1.setText("2. 这是一个点击按钮");ul.add(li1);ul.add(li2);content.add(ul);div.add(span);div.add(a);div.add(input);div.add(content);div.print(0);}
}

<div id="content" style="display:block"><span id="title" style="display:inline">设计模式之组合模式</span><a id="goBaidu" style="display:inline"></a><input id="clickMe" style="display:inline-block;position:absolute;float:left">    </input><div id="description" style="display:block"><ul id="ul" style="display:block"><li id="li-1" style="display:block"></li><li id="li-2" style="display:block"></li></ul></div>
</div>

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《设计模式》12.组合模式（结构型）

角色