Java 8的简单示例:

import java.util.Base64;

String str = "your string";
String encodedStr = Base64.getEncoder().encodeToString(str.getBytes("utf-8"));

要转换这个，你需要一个编码器和解码器，你将从Base64Coder -一个Java中的开源Base64编码器/解码器。你需要的是base64code .java文件。

现在要按你的要求访问这个类，你需要下面的类:

import java.io.BufferedInputStream;
import java.io.BufferedOutputStream;
import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.FileReader;
import java.io.FileWriter;
import java.io.InputStream;
import java.io.IOException;
import java.io.OutputStream;

public class Base64 {

    public static void main(String args[]) throws IOException {
        /*
         * if (args.length != 2) {
         *     System.out.println(
         *         "Command line parameters: inputFileName outputFileName");
         *     System.exit(9);
         * } encodeFile(args[0], args[1]);
         */
        File sourceImage = new File("back3.png");
        File sourceImage64 = new File("back3.txt");
        File destImage = new File("back4.png");
        encodeFile(sourceImage, sourceImage64);
        decodeFile(sourceImage64, destImage);
    }

    private static void encodeFile(File inputFile, File outputFile) throws IOException {
        BufferedInputStream in = null;
        BufferedWriter out = null;
        try {
            in = new BufferedInputStream(new FileInputStream(inputFile));
            out = new BufferedWriter(new FileWriter(outputFile));
            encodeStream(in, out);
            out.flush();
        }
        finally {
            if (in != null)
                in.close();
            if (out != null)
                out.close();
        }
    }

    private static void encodeStream(InputStream in, BufferedWriter out) throws IOException {
        int lineLength = 72;
        byte[] buf = new byte[lineLength / 4 * 3];
        while (true) {
            int len = in.read(buf);
            if (len <= 0)
                break;
            out.write(Base64Coder.encode(buf, 0, len));
            out.newLine();
        }
    }

    static String encodeArray(byte[] in) throws IOException {
        StringBuffer out = new StringBuffer();
        out.append(Base64Coder.encode(in, 0, in.length));
        return out.toString();
    }

    static byte[] decodeArray(String in) throws IOException {
        byte[] buf = Base64Coder.decodeLines(in);
        return buf;
    }

    private static void decodeFile(File inputFile, File outputFile) throws IOException {
        BufferedReader in = null;
        BufferedOutputStream out = null;
        try {
            in = new BufferedReader(new FileReader(inputFile));
            out = new BufferedOutputStream(new FileOutputStream(outputFile));
            decodeStream(in, out);
            out.flush();
        }
        finally {
            if (in != null)
                in.close();
            if (out != null)
                out.close();
        }
    }

    private static void decodeStream(BufferedReader in, OutputStream out) throws IOException {
        while (true) {
            String s = in.readLine();
            if (s == null)
                break;
            byte[] buf = Base64Coder.decodeLines(s);
            out.write(buf);
        }
    }
}

在Android中，您可以将位图转换为Base64以便上传到服务器或web服务。

Bitmap bmImage = //Data
ByteArrayOutputStream baos = new ByteArrayOutputStream();
bmImage.compress(Bitmap.CompressFormat.JPEG, 100, baos);
byte[] imageData = baos.toByteArray();
String encodedImage = Base64.encodeArray(imageData);

这个“encodedImage”是图像的文本表示。你可以使用它来上传或者直接显示在HTML页面中，如下所示(参考):

<img alt="" src="data:image/png;base64,<?php echo $encodedImage; ?>" width="100px" />
<img alt="" src="data:image/png;base64,/9j/4AAQ...........1f/9k=" width="100px" />

文档:http://dwij.co.in/java-base64-image-encoder

如果你坚持使用比8更早的Java版本，但已经在为Java使用AWS SDK，你可以使用com.amazonaws.util.Base64。

我尝试使用以下代码片段。它运行得很好。: -)

com.sun.org.apache.xml.internal.security.utils.Base64.encode("The string to encode goes here");

将这个库添加到应用级依赖项中

实现“org.apache.commons: commons-collections4:4.4”

GZIP + Base64

Base64格式的字符串长度比原始长度大:平均133%。因此，首先用GZIP压缩它，然后编码到Base64是有意义的。对于超过200个字符的字符串，它最多可以减少77%。例子:

public static void main(String[] args) throws IOException {
    byte[] original = randomString(100).getBytes(StandardCharsets.UTF_8);

    byte[] base64 = encodeToBase64(original);
    byte[] gzipToBase64 = encodeToBase64(encodeToGZIP(original));

    byte[] fromBase64 = decodeFromBase64(base64);
    byte[] fromBase64Gzip = decodeFromGZIP(decodeFromBase64(gzipToBase64));

    // test
    System.out.println("Original: " + original.length + " bytes, 100%");
    System.out.println("Base64: " + base64.length + " bytes, "
            + (base64.length * 100 / original.length) + "%");
    System.out.println("GZIP+Base64: " + gzipToBase64.length + " bytes, "
            + (gzipToBase64.length * 100 / original.length) + "%");

    //Original: 3700 bytes, 100%
    //Base64: 4936 bytes, 133%
    //GZIP+Base64: 2868 bytes, 77%

    System.out.println(Arrays.equals(original, fromBase64)); // true
    System.out.println(Arrays.equals(original, fromBase64Gzip)); // true
}

public static byte[] decodeFromBase64(byte[] arr) {
    return Base64.getDecoder().decode(arr);
}

public static byte[] encodeToBase64(byte[] arr) {
    return Base64.getEncoder().encode(arr);
}

public static byte[] decodeFromGZIP(byte[] arr) throws IOException {
    ByteArrayInputStream bais = new ByteArrayInputStream(arr);
    GZIPInputStream gzip = new GZIPInputStream(bais);
    return gzip.readAllBytes();
}

public static byte[] encodeToGZIP(byte[] arr) throws IOException {
    ByteArrayOutputStream baos = new ByteArrayOutputStream();
    GZIPOutputStream gzip = new GZIPOutputStream(baos);
    gzip.write(arr);
    gzip.finish();
    return baos.toByteArray();
}

public static String randomString(int count) {
    StringBuilder str = new StringBuilder();
    for (int i = 0; i < count; i++) {
        str.append(" ").append(UUID.randomUUID().toString());
    }
    return str.toString();
}

请参见:如何获取sun.misc的JAR文件。BASE64Encoder课吗?