浅析Java中XPath和JsonPath以及SpEL的用法与对比

<books>
   <book>
      <title>Java Programming</title>
      <author>James Gosling</author>
   </book>
   <book>
      <title>XML Fundamentals</title>
      <author>John Doe</author>
   </book>
</books>

// 导入所需的XML处理库
import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;
import org.w3c.dom.Document;
import javax.xml.xpath.XPath;
import javax.xml.xpath.XPathFactory;
import javax.xml.xpath.XPathConstants;
import org.w3c.dom.NodeList;

// ...

// 创建DocumentBuilderFactory实例以解析XML文档
DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
// 创建DocumentBuilder实例
DocumentBuilder builder = factory.newDocumentBuilder();
// 解析XML文档，这里假设文件名为books.xml
Document doc = builder.parse("books.xml");
// 创建XPath实例来查询XML文档
XPath xpath = XPathFactory.newInstance().newXPath();
// XPath表达式，用来选择所有的<title>元素
String expression = "/books/book/title";
// 执行XPath查询并获取结果节点列表
NodeList titles = (NodeList) xpath.evaluate(expression, doc, XPathConstants.NODESET);

// 遍历结果节点列表并打印每个<title>元素的文本内容
for (int i = 0; i < titles.getLength(); i++) {
    System.out.println(titles.item(i).getTextContent());
}

{
  "store": {
    "book": [
      { "title": "Clean Code", "author": "Robert C. Martin" },
      { "title": "The Pragmatic Programmer", "author": "Andrew Hunt and David Thomas" }
    ],
    "bicycle": {
      "color": "red",
      "price": 19.95
    }
  }
}

<dependency>
    <groupId>com.jayway.jsonpath</groupId>
    <artifactId>json-path</artifactId>
    <version>2.8.0</version>
</dependency>

// 导入JsonPath库
import com.jayway.jsonpath.JsonPath;
import net.minidev.json.JSONArray;
// ...
// JSON字符串，表示一个书店的存货，包括书籍和自行车
String json = "{ \"store\": { \"book\": [ { \"title\": \"Clean Code\", \"author\": \"Robert C. Martin\" }, { \"title\": \"The Pragmatic Programmer\", \"author\": \"Andrew Hunt and David Thomas\" } ], \"bicycle\": { \"color\": \"red\", \"price\": 19.95 } } }";
// JsonPath表达式，用来选取所有书籍的标题
String jsonPathExpression = "$.store.book[*].title";
// 执行JsonPath查询并获取结果为JSONArray
JSONArray bookTitles = JsonPath.read(json, jsonPathExpression);
// 遍历JSONArray并打印每本书的标题
for (Object title : bookTitles) {
    System.out.println(title);
}

<dependency>
    <groupId>org.noear</groupId>
    <artifactId>snack3</artifactId>
</<dependency>

import org.springframework.expression.ExpressionParser;
import org.springframework.expression.spel.standard.SpelExpressionParser;
import org.springframework.expression.Expression;

// 创建一个表达式解析器
ExpressionParser parser = new SpelExpressionParser();

// 解析一个字符串表达式，并执行字符串拼接
Expression exp = parser.parseExpression("'Hello World'.concat('!')");
String message = (String) exp.getValue();

// 输出结果，将打印：Hello World!
System.out.println(message);

import javax.el.ELProcessor;

// 创建ELProcessor实例
ELProcessor elProcessor = new ELProcessor();

// 定义一个变量并赋值
elProcessor.setValue("greeting", "Hello");

// 使用EL表达式拼接字符串
String result = (String) elProcessor.eval("greeting.concat(' World!')");

// 输出结果，将打印：Hello World!
System.out.println(result);