Java数据库表自动转化为PO对象

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();

    }

}