【开发技巧】驼峰和下划线命名相互转换

开发时，一般数据库的字段命名是下划线风格，Java编程时字段命名一般是驼峰风格。
在实体和域模型创建初期，我们经常需要对同一字段进行命名风格的反复切换。

talk is cheap, show me the code.

测试用例

package com.itplh.generator;

public class ConvertTest {

    public static void main(String[] args) {
        Underline2JavaPrivateFieldConverter.run();

        HumpField2UnderlineConverter.run("D:\\User.java");
    }

}

控制台输出

private String username;
private String createTime;
private String lastUpdateTime;
username
create_time
last_update_time

input.txt

username
create_time
last_update_time

User.java

@Data
public class User {
    private String username;
    private String createTime;
    private String lastUpdateTime;
}

驼峰转下划线

HumpField2UnderlineConverter.java

package com.itplh.generator;

import java.io.BufferedReader;
import java.io.FileReader;
import java.io.IOException;

public class HumpField2UnderlineConverter {

    public static void run(String classAbsolutePath) {
        try (BufferedReader reader = new BufferedReader(new FileReader(classAbsolutePath))) {
            reader.lines()
                    .map(String::trim)
                    .filter(e -> e.startsWith("private "))
                    .map(e -> e.split(" ")[2])
                    .map(e -> e.endsWith(";") ? e.substring(0, e.length() - 1) : e)
                    .map(HumpField2UnderlineConverter::convertHump2Underline)
                    .forEach(System.out::println);
        } catch (IOException e) {
            e.printStackTrace();
        }

    }

    private static String convertHump2Underline(String humpField) {
        StringBuilder underlineField = new StringBuilder();
        for (int i = 0; i < humpField.length(); i++) {
            char c = humpField.charAt(i);
            if (c >= 'A' && c <= 'Z') {
                underlineField.append('_').append((char) (c + 32));
                continue;
            }
            underlineField.append(c);
        }
        return underlineField.toString();
    }

}

PS：也可以使用java.beans.Introspector#getBeanInfo(java.lang.Class<?>, java.lang.Class<?>)来读取类的属性名。

下划线转驼峰

Underline2JavaPrivateFieldConverter.java

package com.itplh.generator;

import java.io.BufferedReader;
import java.io.FileReader;
import java.io.IOException;
import java.util.Arrays;

public class Underline2JavaPrivateFieldConverter {

    public static void run() {
        try (BufferedReader reader = new BufferedReader(new FileReader("CodeGenerator/input.txt"))) {
            reader.lines()
                    .map(e -> e.trim().toLowerCase())
                    .filter(e -> e.length() > 1)
                    .map(line -> {
                        return Arrays.stream(line.split(" "))
                                .findFirst()
                                .map(e -> e.startsWith("`") ? e.substring(1, e.length() - 1) : e)
                                .map(Underline2JavaPrivateFieldConverter::javaPrivateFieldSplicer)
                                .orElse("");
                    }).forEach(System.out::println);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    private static String javaPrivateFieldSplicer(String underlineField) {
        return "private String " + convertUnderline2Hump(underlineField) + ";";
    }

    private static String convertUnderline2Hump(String underlineField) {
        underlineField = underlineField.trim();
        if (underlineField.startsWith("_") || underlineField.endsWith("_")) {
            return underlineField;
        }
        underlineField = underlineField.toLowerCase();

        StringBuilder humpField = new StringBuilder();
        humpField.append(underlineField.charAt(0));
        for (int i = 1; i < underlineField.length(); i++) {
            if ('_' == underlineField.charAt(i)) {
                i++;
                humpField.append((char) (underlineField.charAt(i) - 32));
                continue;
            }
            humpField.append(underlineField.charAt(i));
        }
        return humpField.toString();
    }

}