在番石榴中，这很简单:

Strings.padStart("string", 10, ' ');
Strings.padEnd("string", 10, ' ');

从Java 1.5开始，string. format()可以用于左/右填充给定的字符串。

public static String padRight(String s, int n) {
     return String.format("%-" + n + "s", s);  
}

public static String padLeft(String s, int n) {
    return String.format("%" + n + "s", s);  
}

...

public static void main(String args[]) throws Exception {
 System.out.println(padRight("Howto", 20) + "*");
 System.out.println(padLeft("Howto", 20) + "*");
}

输出为:

Howto               *
               Howto*

使用该函数。

private String leftPadding(String word, int length, char ch) {
   return (length > word.length()) ? leftPadding(ch + word, length, ch) : word;
}

如何使用?

leftPadding(month, 2, '0');

输出: 01 02 03 04 ..11日12

这是一个高效的实用工具类，用于Java中的左填充，右填充，中心填充和零填充字符串。

package com.example;

/**
 * Utility class for left pad, right pad, center pad and zero fill.
 */
public final class StringPadding {

    public static String left(String string, int length, char fill) {

        if (string.length() < length) {

            char[] chars = string.toCharArray();
            char[] output = new char[length];

            int delta = length - chars.length;

            for (int i = 0; i < length; i++) {
                if (i < delta) {
                    output[i] = fill;
                } else {
                    output[i] = chars[i - delta];
                }
            }

            return new String(output);
        }

        return string;
    }

    public static String right(String string, int length, char fill) {

        if (string.length() < length) {

            char[] chars = string.toCharArray();
            char[] output = new char[length];

            for (int i = 0; i < length; i++) {
                if (i < chars.length) {
                    output[i] = chars[i];
                } else {
                    output[i] = fill;
                }
            }

            return new String(output);
        }

        return string;
    }

    public static String center(String string, int length, char fill) {

        if (string.length() < length) {

            char[] chars = string.toCharArray();

            int delta = length - chars.length;
            int a = (delta % 2 == 0) ? delta / 2 : delta / 2 + 1;
            int b = a + chars.length;

            char[] output = new char[length];
            for (int i = 0; i < length; i++) {
                if (i < a) {
                    output[i] = fill;
                } else if (i < b) {
                    output[i] = chars[i - a];
                } else {
                    output[i] = fill;
                }
            }

            return new String(output);
        }

        return string;
    }

    public static String zerofill(String string, int length) {
        return left(string, length, '0');
    }

    private StringPadding() {
    }

    /**
     * For tests!
     */
    public static void main(String[] args) {

        String string = "123";
        char blank = ' ';

        System.out.println("left pad:    [" + StringPadding.left(string, 10, blank) + "]");
        System.out.println("right pad:   [" + StringPadding.right(string, 10, blank) + "]");
        System.out.println("center pad:  [" + StringPadding.center(string, 10, blank) + "]");
        System.out.println("zero fill:   [" + StringPadding.zerofill(string, 10) + "]");
    }
}

输出如下:

left pad:    [       123]
right pad:   [123       ]
center pad:  [    123   ]
zero fill:   [0000000123]

public static String padLeft(String in, int size, char padChar) {                
    if (in.length() <= size) {
        char[] temp = new char[size];
        /* Llenado Array con el padChar*/
        for(int i =0;i<size;i++){
            temp[i]= padChar;
        }
        int posIniTemp = size-in.length();
        for(int i=0;i<in.length();i++){
            temp[posIniTemp]=in.charAt(i);
            posIniTemp++;
        }            
        return new String(temp);
    }
    return "";
}

为此编写自己的函数可能比其他答案更简单。

private static String padRight(String str, String padChar, int n) {

    String paddedString = str;

    while (paddedString.length() < n) {

        paddedString = padChar + str;

    }

    return paddedString;

}

private static String padLeft(String str, String padChar, int n) {

    String paddedString = str;

    while (paddedString.length() < n) {

        paddedString += padChar;

    }

    return paddedString;

}