今天就跟大家聊聊有关如何利用Java实现全文检索功能，可能很多人都不太了解，为了让大家更加了解，小编给大家总结了以下内容，希望大家根据这篇文章可以有所收获。
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第一步，构建Trie树，定义Node类型：
/**
* Created by zhaoyy on 2017/2/7.
*/
interface Node {
char value();
boolean exists();
boolean isRoot();
Node parent();
Node childOf(char c);
Node fail();
void setFail(Node node);
void setExists(boolean exists);
void add(Node child);
List children();
}第二步，实现两种Node，如果词汇全是可打印的ASCII字符，就采用AsciiNode，否则（比如包含汉字），使用基于hash表的MapNode；这两种Node均集成自AbstractNode:
/**
* Created by zhaoyy on 2017/2/8.
*/
abstract class AbstractNode implements Node {
private static final char EMPTY = '\0';
private final char value;
private final Node parent;
private boolean exists;
private Node fail;
public AbstractNode(Node parent, char value) {
this.parent = parent;
this.value = value;
this.exists = false;
this.fail = null;
}
public AbstractNode() {
this(null, EMPTY);
}
private static String tab(int n) {
StringBuilder builder = new StringBuilder();
for (int i = 0; i < n; i++) {
builder.append('\t');
}
return builder.toString();
}
private static String toString(Node node, int depth) {
StringBuilder builder = new StringBuilder();
String tab = tab(depth);
Node fail = node.fail();
Node parent = node.parent();
builder
.append(tab)
.append('<')
.append(node.value())
.append(" exists=\"")
.append(node.exists())
.append('"')
.append(" parent=\"")
.append(parent == null ? "null" : parent.value())
.append('"')
.append(" fail=\"")
.append(fail == null ? "null" : fail.value())
.append("\">\r\n");
for (Node child : node.children())
builder.append(toString(child, depth + 1));
builder
.append(tab)
.append("\r\n");
return builder.toString();
}
@Override
public char value() {
return value;
}
@Override
public boolean exists() {
return exists;
}
@Override
public boolean isRoot() {
return value == EMPTY;
}
@Override
public Node parent() {
return parent;
}
@Override
public Node fail() {
return fail;
}
@Override
public void setFail(Node node) {
this.fail = node;
}
@Override
public void setExists(boolean exists) {
this.exists = exists;
}
@Override
public String toString() {
return toString(this, 0);
}
}
/////////////////////////////////////////////////////////////////////////////////////////////
/**
* Created by zhaoyy on 2017/2/8.
*/
final class AsciiNode extends AbstractNode implements Node {
private static final char FROM = 32;
private static final char TO = 126;
private final Node[] children;
public AsciiNode() {
super();
this.children = new Node[TO - FROM + 1];
}
public AsciiNode(Node parent, char value) {
super(parent, value);
this.children = new Node[TO - FROM + 1];
}
@Override
public Node childOf(char c) {
if (c >= FROM && c <= TO)
return children[(int) c - FROM];
else return null;
}
@Override
public void add(Node child) {
int index = (int) child.value();
children[index - FROM] = child;
}
@Override
public List children() {
List nodes = new ArrayList();
for (Node child : children)
if (child != null)
nodes.add(child);
return nodes;
}
}
//////////////////////////////////////////////////////////////////////////////////////////////
/**
* Created by zhaoyy on 2017/2/8.
*/
final class MapNode extends AbstractNode implements Node {
private final Map children;
public MapNode() {
super();
this.children = new HashMap();
}
public MapNode(Node parent, char value) {
super(parent, value);
this.children = new HashMap();
}
@Override
public Node childOf(char c) {
return children.get(c);
}
@Override
public void add(Node child) {
children.put(child.value(), child);
}
@Override
public List children() {
List nodes = new ArrayList();
nodes.addAll(children.values());
return nodes;
}
}第三步，
首先定义一个Node构造器：
/**
* Created by zhaoyy on 2017/2/8.
*/
public interface NodeMaker {
Node make(Node parent, char value);
Node makeRoot();
}然后构建AC自动机，实现创建及查找方法：
/**
* Created by zhaoyy on 2017/2/7.
*/
public final class WordTable {
private final Node root;
private WordTable(Collection<? extends CharSequence> words, NodeMaker maker) {
Node root = buildTrie(words, maker);
setFailNode(root);
this.root = root;
}
public static WordTable compile(Collection<? extends CharSequence> words) {
if (words == null || words.isEmpty())
throw new IllegalArgumentException();
final NodeMaker maker;
if (isAscii(words))
maker = new NodeMaker() {
@Override
public Node make(Node parent, char value) {
return new AsciiNode(parent, value);
}
@Override
public Node makeRoot() {
return new AsciiNode();
}
};
else maker = new NodeMaker() {
@Override
public Node make(Node parent, char value) {
return new MapNode(parent, value);
}
@Override
public Node makeRoot() {
return new MapNode();
}
};
return new WordTable(words, maker);
}
private static boolean isAscii(Collection<? extends CharSequence> words) {
for (CharSequence word : words) {
int len = word.length();
for (int i = 0; i < len; i++) {
int c = (int) word.charAt(i);
if (c < 32 || c > 126)
return false;
}
}
return true;
}
private static Node buildTrie(Collection<? extends CharSequence> sequences, NodeMaker maker) {
Node root = maker.makeRoot();
for (CharSequence sequence : sequences) {
int len = sequence.length();
Node current = root;
for (int i = 0; i < len; i++) {
char c = sequence.charAt(i);
Node node = current.childOf(c);
if (node == null) {
node = maker.make(current, c);
current.add(node);
}
current = node;
if (i == len - 1)
node.setExists(true);
}
}
return root;
}
private static void setFailNode(final Node root) {
root.setFail(null);
Queue queue = new LinkedList();
queue.add(root);
while (!queue.isEmpty()) {
Node parent = queue.poll();
Node temp;
for (Node child : parent.children()) {
if (parent.isRoot())
child.setFail(root);
else {
temp = parent.fail();
while (temp != null) {
Node node = temp.childOf(child.value());
if (node != null) {
child.setFail(node);
break;
}
temp = temp.fail();
}
if (temp == null)
child.setFail(root);
}
queue.add(child);
}
}
}
public boolean findAnyIn(CharSequence cs) {
int len = cs.length();
Node node = root;
for (int i = 0; i < len; i++) {
Node next = node.childOf(cs.charAt(i));
if (next == null) {
next = node.fail();
if (next == null) {
node = root;
continue;
}
}
if (next.exists())
return true;
}
return false;
}
public List search(CharSequence cs) {
if (cs == null || cs.length() == 0)
return Collections.emptyList();
List result = new ArrayList();
int len = cs.length();
Node node = root;
for (int i = 0; i < len; i++) {
Node next = node.childOf(cs.charAt(i));
if (next == null) {
next = node.fail();
if (next == null) {
node = root;
continue;
}
}
if (next.exists()) {
MatchInfo info = new MatchInfo(i, next);
result.add(info);
node = root;
continue;
}
node = next;
}
return result;
}
@Override
public String toString() {
return root.toString();
}
}定义一个保存查找结果的实体：
/**
* Created by zhaoyy on 2017/2/7.
*/
public final class MatchInfo {
private final int index;
private final String word;
public MatchInfo(int index, String word) {
this.index = index;
this.word = word;
}
public MatchInfo(int index, Node node) {
StringBuilder builder = new StringBuilder();
while (node != null) {
if (!node.isRoot())
builder.append(node.value());
node = node.parent();
}
String word = builder.reverse().toString();
this.index = index + 1 - word.length();
this.word = word;
}
public int getIndex() {
return index;
}
public String getWord() {
return word;
}
@Override
public String toString() {
return index + ":" + word;
}
}第四步，调用Demo：
public static void main(String[] args) {
List list = Arrays.asList("say", "her", "he", "she", "shr", "alone");
WordTable table = WordTable.compile(list);
System.out.println(table);
System.out.println(table.search("1shesaynothingabouthislivinghimalone"));
}以下是输出结果：
< exists="false" parent="null" fail="null">
[1:she, 4:say, 31:alone]
看完上述内容，你们对如何利用Java实现全文检索功能有进一步的了解吗？如果还想了解更多知识或者相关内容，请关注创新互联行业资讯频道，感谢大家的支持。
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