java - 从字节数组中编码字符串问题

Question

我有以下方法:

 /**
  * Encodes the byte array into base64 string
  * @param imageByteArray - byte array
  * @return String a {@link java.lang.String}
  */
public static String encodeImage(byte[] imageByteArray) {
    return Base64.encodeBase64URLSafeString(imageByteArray);
}

我正在导入“org.apache.commons.codec.binary.Base64;”但是，我收到错误:

该行有多个标记 - 方法encodeBase64URLSafeString(byte[]) 未定义 类型 Base64 - 行断点:MySQLConnection [行:287] -encodeImage(byte[])

我从“http://www.myjeeva.com/2012/07/how-to-convert-image-to-string-and-string-to-image-in-java/ ”复制了这段代码。我正在使用 Eclipse Juno(完全更新)和 GWT。

有人知道我在这里做错了什么吗？

问候，

格林

谢谢 Markus A。我现在已经根据您的信息创建了这个类:

package org.AwardTracker.server;

public class Base64Decode {
private final static String base64chars = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";

public static byte[] decode(String s) {

    // remove/ignore any characters not in the base64 characters list
    // or the pad character -- particularly newlines
    s = s.replaceAll("[^" + base64chars + "=]", "");

    // replace any incoming padding with a zero pad (the 'A' character is
    // zero)
    String p = (s.charAt(s.length() - 1) == '=' ? (s.charAt(s.length() - 2) == '=' ? "AA"
            : "A")
            : "");

    s = s.substring(0, s.length() - p.length()) + p;
    int resLength = (int) Math.ceil(((float) (s.length()) / 4f) * 3f);
    byte[] bufIn = new byte[resLength];
    int bufIn_i = 0;

    // increment over the length of this encrypted string, four characters
    // at a time
    for (int c = 0; c < s.length(); c += 4) {

        // each of these four characters represents a 6-bit index in the
        // base64 characters list which, when concatenated, will give the
        // 24-bit number for the original 3 characters
        int n = (base64chars.indexOf(s.charAt(c)) << 18)
                + (base64chars.indexOf(s.charAt(c + 1)) << 12)
                + (base64chars.indexOf(s.charAt(c + 2)) << 6)
                + base64chars.indexOf(s.charAt(c + 3));

        // split the 24-bit number into the original three 8-bit (ASCII)
        // characters

        char c1 = (char) ((n >>> 16) & 0xFF);
        char c2 = (char) ((n >>>8) & 0xFF);
        char c3 = (char) (n & 0xFF);

        bufIn[bufIn_i++] = (byte) c1;
        bufIn[bufIn_i++] = (byte) c2;
        bufIn[bufIn_i++] = (byte) c3;

    }

    return bufIn;
}


}

并将调用更改为: 导入 org.AwardTracker.server.Base64Decode;

public static String encodeImage(byte[] imageByteArray) {
    return Base64Decode(imageByteArray); [Error on this line]
}

我现在收到错误:

该行有多个标记 - 类型的方法 Base64Decode(byte[]) 未定义 MySQL连接

非常感谢您的帮助。

问候，

格林

第三轮

好的，所以我的加密和解密方式是错误的。此问题现已更正并放置在正确的库中。但是我的encodeImage方法仍然有错误。这是我用来调用encodeImage方法的方法。我怀疑这些行:

java.sql.Blob imageBlob = result.getBlob(1);
byte[] imageData = imageBlob.getBytes(1, (int) imageBlob.length());

不正确。但是，我已将 ImageData 定义为 byte[]，所以我不明白为什么encodeImage 认为它是一个 String？

public String getImageData(String id){
    ResultSet result = null;
    PreparedStatement ps = null;
    String imageDataString = null;
    try {
        // Read in the image from the database.
        ps = conn.prepareStatement(
              "SELECT at_cub_details.cd_photograph " +
                      "FROM at_cub_details " + 
                      "WHERE at_cub_details.cd_id = \"" + id + "\"");
        result = ps.executeQuery();
        while (result.next()) {
            java.sql.Blob imageBlob = result.getBlob(1);
            byte[] imageData = imageBlob.getBytes(1, (int) imageBlob.length());

            //Convert Image byte array into Base64 String
            imageDataString = encodeImage(imageData);
        }

    }

导致错误:

public static String encodeImage(byte[] imageByteArray) {
    return Base64Encode.encode(imageByteArray); [Error on this line]
}

“Base64Encode 类型中的方法encode(String) 不适用于参数 (byte[])”

感谢您的帮助。

问候，

格林

p.s.，我认为当我完成时，这值得写一篇博客，因为我在这个领域找不到任何确定的工作，而且我本以为这会被经常使用。我的下一个项目。

编码类是:

package org.AwardTracker.server;

public class Base64Encode {
private final static String base64chars = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";

public static String encode(String s) {

    // the result/encoded string, the padding string, and the pad count
    String r = "", p = "";
    int c = s.length() % 3;

    // add a right zero pad to make this string a multiple of 3 characters
    if (c > 0) {
        for (; c < 3; c++) {
            p += "=";
            s += "\0";
        }
    }

    // increment over the length of the string, three characters at a time
    for (c = 0; c < s.length(); c += 3) {

        // we add newlines after every 76 output characters, according to
        // the MIME specs
        if (c > 0 && (c / 3 * 4) % 76 == 0)
            r += "\r\n";

        // these three 8-bit (ASCII) characters become one 24-bit number
        int n = (s.charAt(c) << 16) + (s.charAt(c + 1) << 8)
                + (s.charAt(c + 2));

        // this 24-bit number gets separated into four 6-bit numbers
        int n1 = (n >> 18) & 63, n2 = (n >> 12) & 63, n3 = (n >> 6) & 63, n4 = n & 63;

        // those four 6-bit numbers are used as indices into the base64
        // character list
        r += "" + base64chars.charAt(n1) + base64chars.charAt(n2)
                + base64chars.charAt(n3) + base64chars.charAt(n4);
    }

    return r.substring(0, r.length() - p.length()) + p;
}
}

解码类是:

package org.AwardTracker.server;

public class Base64Decode {
private final static String base64chars = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";

public static byte[] decode(String s) {

    // remove/ignore any characters not in the base64 characters list
    // or the pad character -- particularly newlines
    s = s.replaceAll("[^" + base64chars + "=]", "");

    // replace any incoming padding with a zero pad (the 'A' character is
    // zero)
    String p = (s.charAt(s.length() - 1) == '=' ? (s.charAt(s.length() - 2) == '=' ? "AA"
            : "A")
            : "");

    s = s.substring(0, s.length() - p.length()) + p;
    int resLength = (int) Math.ceil(((float) (s.length()) / 4f) * 3f);
    byte[] bufIn = new byte[resLength];
    int bufIn_i = 0;

    // increment over the length of this encrypted string, four characters
    // at a time
    for (int c = 0; c < s.length(); c += 4) {

        // each of these four characters represents a 6-bit index in the
        // base64 characters list which, when concatenated, will give the
        // 24-bit number for the original 3 characters
        int n = (base64chars.indexOf(s.charAt(c)) << 18)
                + (base64chars.indexOf(s.charAt(c + 1)) << 12)
                + (base64chars.indexOf(s.charAt(c + 2)) << 6)
                + base64chars.indexOf(s.charAt(c + 3));

        // split the 24-bit number into the original three 8-bit (ASCII)
        // characters

        char c1 = (char) ((n >>> 16) & 0xFF);
        char c2 = (char) ((n >>>8) & 0xFF);
        char c3 = (char) (n & 0xFF);

        bufIn[bufIn_i++] = (byte) c1;
        bufIn[bufIn_i++] = (byte) c2;
        bufIn[bufIn_i++] = (byte) c3;

    }

    return bufIn;
}


}

我终于找到了一个有效的编码类:

package org.AwardTracker.server;

public class Base64Encode2 {
 private final static char[] ALPHABET = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/".toCharArray();

    private static int[]  toInt   = new int[128];

    static {
        for(int i=0; i< ALPHABET.length; i++){
            toInt[ALPHABET[i]]= i;
        }
    }

/**
 * Translates the specified byte array into Base64 string.
 *
 * @param buf the byte array (not null)
 * @return the translated Base64 string (not null)
 */
public static String encode(byte[] buf){
    int size = buf.length;
    char[] ar = new char[((size + 2) / 3) * 4];
    int a = 0;
    int i=0;
    while(i < size){
        byte b0 = buf[i++];
        byte b1 = (i < size) ? buf[i++] : 0;
        byte b2 = (i < size) ? buf[i++] : 0;

        int mask = 0x3F;
        ar[a++] = ALPHABET[(b0 >> 2) & mask];
        ar[a++] = ALPHABET[((b0 << 4) | ((b1 & 0xFF) >> 4)) & mask];
        ar[a++] = ALPHABET[((b1 << 2) | ((b2 & 0xFF) >> 6)) & mask];
        ar[a++] = ALPHABET[b2 & mask];
    }
    switch(size % 3){
        case 1: ar[--a]  = '=';
        case 2: ar[--a]  = '=';
    }
    return new String(ar);
}

}

感谢 Markus A 的所有帮助。非常感谢。

问候，

格林

Answer 1

GWT 不提供 apache commons 包，因此我认为您无法在代码中使用此函数。

以下是您可以在 GWT 中使用的内容:

https://developers.google.com/web-toolkit/doc/latest/RefJreEmulation

如果您确实想使用它，您实际上需要拥有 Base64 类(及其所有依赖项)的源代码，并将其放入项目中 GWT 编译器可以访问它以将其转换为 JavaScript 的位置。

有关进行编码的其他方法，请参见此处:

How do I encode/decode short strings as Base64 using GWT?

添加到原始帖子中的新问题:

对于初学者，您需要在类上调用静态函数，如下所示:

return Base64Decode.decode(imageByteArray);

但是您的类型似乎也向后:encodeImage 接受一个 byte[] 并返回一个 String，而 Base64Decode.decode 接受一个 String 并返回一个 byte[]。您可能需要使用等效的 Base64Encode.encode 函数而不是解码函数。