我搜索了一个如何在Java中压缩字符串的示例。
我有一个压缩然后解压缩的功能。压缩似乎工作正常:
public static String encStage1(String str)
{
String format1 = "ISO-8859-1";
String format2 = "UTF-8";
if (str == null || str.length() == 0)
{
return str;
}
System.out.println("String length : " + str.length());
ByteArrayOutputStream out = new ByteArrayOutputStream();
String outStr = null;
try
{
GZIPOutputStream gzip = new GZIPOutputStream(out);
gzip.write(str.getBytes());
gzip.close();
outStr = out.toString(format2);
System.out.println("Output String lenght : " + outStr.length());
} catch (Exception e)
{
e.printStackTrace();
}
return outStr;
}
但反过来抱怨字符串不是GZIP格式,即使我将encStage1的返回值直接传递回decStage3:
public static String decStage3(String str)
{
if (str == null || str.length() == 0)
{
return str;
}
System.out.println("Input String length : " + str.length());
String outStr = "";
try
{
String format1 = "ISO-8859-1";
String format2 = "UTF-8";
GZIPInputStream gis = new GZIPInputStream(new ByteArrayInputStream(str.getBytes(format2)));
BufferedReader bf = new BufferedReader(new InputStreamReader(gis, format2));
String line;
while ((line = bf.readLine()) != null)
{
outStr += line;
}
System.out.println("Output String lenght : " + outStr.length());
} catch (Exception e)
{
e.printStackTrace();
}
return outStr;
}
当我使用encStage1的字符串返回调用时,我收到此错误:
public String encIDData(String idData)
{
String tst = "A simple test string";
System.out.println("Enc 0: " + tst);
String stg1 = encStage1(tst);
System.out.println("Enc 1: " + toHex(stg1));
String dec1 = decStage3(stg1);
System.out.println("unzip: " + toHex(dec1));
}
输出/错误:
Enc 0: A simple test string
String length : 20
Output String lenght : 40
Enc 1: 1fefbfbd0800000000000000735428efbfbdefbfbd2defbfbd495528492d2e51282e29efbfbdefbfbd4b07005aefbfbd21efbfbd14000000
Input String length : 40
java.io.IOException: Not in GZIP format
at java.util.zip.GZIPInputStream.readHeader(GZIPInputStream.java:137)
at java.util.zip.GZIPInputStream.<init>(GZIPInputStream.java:58)
at java.util.zip.GZIPInputStream.<init>(GZIPInputStream.java:68)
答案 0 :(得分:4)
一个小错误是:
gzip.write(str.getBytes());
采用默认的平台编码,在Windows上永远不会是ISO-8859-1。更好:
gzip.write(str.getBytes(format1));
您可以考虑使用“Cp1252”,Windows Latin-1(对于某些欧洲语言),而不是“ISO-8859-1”,Latin-1。这会引用逗号等引号等。
主要错误是将压缩字节转换为String。 Java将二进制数据(byte [],InputStream,OutputStream)与文本(String,char,Reader,Writer)分开,内部始终以Unicode格式保存。字节序列不需要是有效的UTF-8。您可以通过将字节转换为单字节编码(例如ISO-8859-1)来逃避。
最好的方法是
gzip.write(str.getBytes(StandardCharsets.UTF_8));
所以你有完整的Unicode,每个脚本都可以合并。
并解压缩为ByteArrayOutputStream
和new String(baos.toByteArray(), StandardCharsets.UTF_8)
。
在带有UTF-8的InputStreamReader上使用BufferedReader也没关系,但readLine会抛弃换行符
outStr += line + "\r\n"; // Or so.
干净答案:
public static byte[] encStage1(String str) throws IOException
{
try (ByteArrayOutputStream out = new ByteArrayOutputStream())
{
try (GZIPOutputStream gzip = new GZIPOutputStream(out))
{
gzip.write(str.getBytes(StandardCharsets.UTF_8));
}
return out.toByteArray();
//return out.toString(StandardCharsets.ISO_8859_1);
// Some single byte encoding
}
}
public static String decStage3(byte[] str) throws IOException
{
ByteArrayOutputStream baos = new ByteArrayOutputStream();
try (GZIPInputStream gis = new GZIPInputStream(new ByteArrayInputStream(str)))
{
int b;
while ((b = gis.read()) != -1) {
baos.write((byte) b);
}
}
return new String(baos.toByteArray(), StandardCharset.UTF_8);
}
答案 1 :(得分:3)
使用toString / getBytes进行编码/解码是一种错误的方法。尝试使用类似BASE64编码的东西(jdk 1.8中的java.util.Base64)
作为证明尝试这个简单的测试:
import org.testng.annotations.Test;
import java.io.ByteArrayOutputStream;
import static org.testng.Assert.assertEquals;
public class SimpleTest {
@Test
public void test() throws Exception {
final String CS = "utf-8";
byte[] b0 = {(byte) 0xff};
ByteArrayOutputStream out = new ByteArrayOutputStream();
out.write(b0);
out.close();
byte[] b1 = out.toString(CS).getBytes(CS);
assertEquals(b0, b1);
}
}