响应式API设计实战：设计一个sax解析包装器

1. 本文组合了Lamda和响应式，设计出一个解析xml的自定义组件，目标是练习新型 API的设计

2. 案例如下：

（1）book.xml

<books>
    <book id="b01">
        <name>john</name>
        <price>23.45</price>
    </book>
    <book id="b02">
        <name>tom</name>
        <price>98</price>
    </book>
</books>

(2) 组件及测试代码：

package cn.johnyu.sax;

import org.xml.sax.Attributes;
import org.xml.sax.SAXException;
import org.xml.sax.helpers.DefaultHandler;

import javax.xml.parsers.SAXParser;
import javax.xml.parsers.SAXParserFactory;
import java.io.File;
import java.util.ArrayList;
import java.util.List;
import java.util.function.Consumer;

class Book {
    private String id;
    private String name;
    private double price;

    public String getId() {
        return id;
    }

    public void setId(String id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

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

    public double getPrice() {
        return price;
    }

    public void setPrice(double price) {
        this.price = price;
    }

    @Override
    public String toString() {
        return "Book{" +
                "id='" + id + '\'' +
                ", name='" + name + '\'' +
                ", price=" + price +
                '}';
    }
}

/**
 * 这是设计出的核心API,使用了"Lamda+响应式api"
 */
class MyXmlBooksHandler extends DefaultHandler {
    private List<Book> books = null;
    private Book book = null;
    private String info;
    private Consumer<List<Book>> bookListConsumer;
    private Consumer<Book> bookConsumer;

    /**
     *
     * @param bookConsumer :每本图书的回调接口
     * @param bookListConsumer: 所有图书的回调接口
     */
    public MyXmlBooksHandler(Consumer<Book> bookConsumer, Consumer<List<Book>> bookListConsumer) {
        this.bookListConsumer = bookListConsumer;
        this.bookConsumer = bookConsumer;
    }

    /**
     * 遇到文档开始，实例化图书，并设置id
     */
    @Override
    public void startElement(String uri, String localName, String qName, Attributes attributes) throws SAXException {
        if ("books".equals(qName)) {
            books = new ArrayList<>();
        }
        if ("book".equals(qName)) {
            book = new Book();
            String id = attributes.getValue("id");
            book.setId(id);
        }
    }

    @Override
    public void characters(char[] ch, int start, int length) throws SAXException {
        String info = new String(ch, start, length).trim();
        this.info = info.isEmpty() ? "" : info;
    }
    /**
     * 遇到文档结束：
     * （1）根据qname,使用info设置图书的各个属性
     * （2）如果遇到的book的结尾，则根据情况要么"消费book"或者"加入到集合中"
     */
    @Override
    public void endElement(String uri, String localName, String qName) throws SAXException {
        if ("name".equals((qName))) {
            book.setName(info);
        }
        if ("price".equals(qName)) {
            try {
                double price = Double.parseDouble(info);
                book.setPrice(price);
            } catch (NumberFormatException e) {
                throw new SAXException("价格数据解析失败");
            }
        }

        if ("book".equals(qName)) {
            //每本书进行一次消费
            if (this.bookConsumer != null) {
                bookConsumer.accept(book);
            }
            if (this.bookListConsumer != null) {
                books.add(book);
            }
        }
    }
    //全部文档结尾的事件中，处理"全部图书的消费"
    @Override
    public void endDocument() throws SAXException {
        if (bookListConsumer != null) {
            bookListConsumer.accept(books);
        }
    }
}

public class MyApp {

    public static void main(String[] args) throws Exception {
        SAXParser parser = SAXParserFactory.newInstance().newSAXParser();
        File file = new File("books.xml");

        //针对每本书进行消费
        MyXmlBooksHandler handler = new MyXmlBooksHandler(System.out::println, null);
        parser.parse(file, handler);


        //针对所有的书进行消费
        MyXmlBooksHandler handler1 = new MyXmlBooksHandler(null, System.out::println);
        parser.parse(file, handler1);
    }
}