本程序简单实现了数据库内省，生成PO对象。
数据库内省有如下两种实现方式：

• 通过mysql元表
• 通过desc table，show tables等命令

import java.io.IOException;
import java.io.PrintWriter;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.sql.*;
import java.util.ArrayList;
import java.util.List;public class Generator {class Table {String name;List<String> fieldList = new ArrayList<>();List<String> typeList = new ArrayList<>();}final static String database = "valley";final static String url = "jdbc:mysql://localhost:3306/" + database + "?serverTimezone=Asia/Shanghai";final static String user = "root", password = "123";final static String targetFolder = "src/main/java/valley/po";final static String packageName="valley.po";final static String tab = "  ";final static List<Table> tables = new ArrayList<>();String convertType(String sqlType) {if (sqlType.startsWith("varchar")) return "String";if (sqlType.startsWith("bigint")) return "Long";if (sqlType.startsWith("int")) return "Integer";if (sqlType.startsWith("smallint")) return "Short";if (sqlType.startsWith("tinyint")) return "Byte";if(sqlType.startsWith("double"))return "Double";return null;}String convertField(String field) {return field;}//表名中只允许字母和下划线,并且下划线不能连续两道String convertTableName(String name) {StringBuilder builder = new StringBuilder();if (name.charAt(0) != '_') builder.append(Character.toUpperCase(name.charAt(0)));for (int i = 1; i < name.length(); i++) {if (name.charAt(i) == '_') continue;if (name.charAt(i - 1) == '_') {builder.append(Character.toUpperCase(name.charAt(i)));} else {builder.append(name.charAt(i));}}builder.append("Po");return builder.toString();}String uppercaseFirstLetter(String s) {return Character.toUpperCase(s.charAt(0)) + s.substring(1);}void writeTableToFile(Table table, PrintWriter writer) {StringBuilder fields = new StringBuilder();StringBuilder gettersAndSetters = new StringBuilder();for (int i = 0; i < table.fieldList.size(); i++) {String field = table.fieldList.get(i), type = table.typeList.get(i);fields.append(String.format("\t%s %s;\n", type, field));String uppercase = uppercaseFirstLetter(field);gettersAndSetters.append(String.format("\t%s get%s(){\n\t\treturn %s;\n\t}\n", type, uppercase, field));gettersAndSetters.append(String.format("\tvoid set%s(%s a%s){\n\t\t%s=a%s;\n\t}\n", uppercase, type, uppercase, field, uppercase));}String ans = String.format("package %s;\n\nclass %s{\n%s\n%s\n}",packageName, table.name, fields, gettersAndSetters);ans = ans.replace("\t", tab);writer.printf(ans);writer.close();}void output() throws IOException {Path folder = Paths.get(targetFolder);if (Files.exists(folder) == false) {Files.createDirectory(folder);}for (Table i : tables) {Path file = folder.resolve(i.name + ".java");writeTableToFile(i, new PrintWriter(Files.newBufferedWriter(file)));}}void init() throws Exception {Class.forName("com.mysql.jdbc.Driver");Connection connection = DriverManager.getConnection(url, user, password);Statement showTablesStatement = connection.createStatement();ResultSet showTablesResultSet = showTablesStatement.executeQuery("show tables");while (showTablesResultSet.next()) {Table t = new Table();t.name = convertTableName(showTablesResultSet.getString(1));Statement descTableStatement = connection.createStatement();ResultSet descTableResult = descTableStatement.executeQuery("desc " + showTablesResultSet.getString(1));while (descTableResult.next()) {t.fieldList.add(convertField(descTableResult.getString(1)));t.typeList.add(convertType(descTableResult.getString(2)));}tables.add(t);descTableResult.close();descTableStatement.close();}showTablesResultSet.close();showTablesStatement.close();connection.close();}Generator() throws Exception {init();output();}public static void main(String[] args) throws Exception {new Generator();}
}