springboot项目 java写一个工具类，查找出mysql数据库中其中一个库的所有表和字段和字段长度并生成一个xml文件

可以使用JDBC API连接MySQL数据库，使用ResultSet获取库中的表和字段信息，再利用DOM API动态生成一个XML格式的文件。以下是一个简单的示例：

import java.io.File;
import java.io.FileOutputStream;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.Statement;

import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;
import javax.xml.transform.OutputKeys;
import javax.xml.transform.Transformer;
import javax.xml.transform.TransformerFactory;
import javax.xml.transform.dom.DOMSource;
import javax.xml.transform.stream.StreamResult;

import org.w3c.dom.Document;
import org.w3c.dom.Element;

public class MysqlSchemaToXmlUtil {

    public static void generateXml(String jdbcUrl, String username, String password, String databaseName, String xmlFilePath)
            throws Exception {
        Class.forName("com.mysql.jdbc.Driver");
        Connection conn = DriverManager.getConnection(jdbcUrl, username, password);
        Statement stmt = conn.createStatement();

        // Get all table names in the database
        String sql = "SELECT TABLE_NAME FROM information_schema.TABLES WHERE TABLE_SCHEMA = '" + databaseName + "'";
        ResultSet rs = stmt.executeQuery(sql);
        
        // Create the document builder and factory
        DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();
        DocumentBuilder db = dbf.newDocumentBuilder();
        Document doc = db.newDocument();

        // Create the root element for the XML file
        Element root = doc.createElement("database");
        root.setAttribute("name", databaseName);
        doc.appendChild(root);

        // Iterate through each table and its columns
        while (rs.next()) {
            String tableName = rs.getString("TABLE_NAME");

            Element table = doc.createElement("table");
            table.setAttribute("name", tableName);
            root.appendChild(table);

            sql = "SELECT COLUMN_NAME, DATA_TYPE, CHARACTER_MAXIMUM_LENGTH FROM information_schema.COLUMNS WHERE TABLE_SCHEMA='"
                    + databaseName + "' AND TABLE_NAME='" + tableName + "'";
            ResultSet columns = stmt.executeQuery(sql);

            while (columns.next()) {
                Element column = doc.createElement("column");
                column.setAttribute("name", columns.getString("COLUMN_NAME"));
                column.setAttribute("type", columns.getString("DATA_TYPE"));
                column.setAttribute("length", columns.getString("CHARACTER_MAXIMUM_LENGTH"));
                table.appendChild(column);
            }
            columns.close();
        }
        rs.close();
        stmt.close();
        conn.close();

        // Write the document to a file
        TransformerFactory transFactory = TransformerFactory.newInstance();
        Transformer trans = transFactory.newTransformer();

        trans.setOutputProperty(OutputKeys.ENCODING, "UTF-8");
        trans.setOutputProperty(OutputKeys.INDENT, "yes");

        DOMSource domSource = new DOMSource(doc);
        File xmlFile = new File(xmlFilePath);
        FileOutputStream fos = new FileOutputStream(xmlFile);

        StreamResult streamResult = new StreamResult(fos);
        trans.transform(domSource, streamResult);
        fos.close();
    }

}

调用示例：

String jdbcUrl = "jdbc:mysql://localhost:3306/test";
String username = "root";
String password = "root";
String databaseName = "test";
String xmlFilePath = "schema.xml";

MysqlSchemaToXmlUtil.generateXml(jdbcUrl, username, password, databaseName, xmlFilePath);

该示例将在本地的test数据库中查找所有表和字段，生成一个名为"schema.xml"的XML文件。