11. Deflater压缩与Inflater解压

一灰灰blogJavaJDKJDK约 1185 字大约 4 分钟

在实际的应用场景中，特别是对外传输数据时，将原始数据压缩之后丢出去，可以说是非常常见的一个case了，平常倒是没有直接使用JDK原生的压缩工具类，使用Protosutff和Kryo的机会较多,正好在实际的工作场景中遇到了，现在简单的看下使用姿势

I. 压缩与解压工具类

1. 基本实现

主要借助的就是Deflater, Inflater两个工具类，其使用姿势如下

public static String uncompress(byte[] input) throws IOException {
    Inflater inflater = new Inflater();
    inflater.setInput(input);
    ByteArrayOutputStream baos = new ByteArrayOutputStream(input.length);
    try {
        byte[] buff = new byte[1024];
        while (!inflater.finished()) {
            int count = inflater.inflate(buff);
            baos.write(buff, 0, count);
        }
    } catch (Exception e) {
        e.printStackTrace();
    } finally {
        baos.close();
    }
    inflater.end();
    byte[] output = baos.toByteArray();
    return new String(output, "UTF-8");
}

public static byte[] compress(byte[] data) throws IOException {
    byte[] output;
    Deflater compress = new Deflater();

    compress.reset();
    compress.setInput(data);
    compress.finish();
    ByteArrayOutputStream bos = new ByteArrayOutputStream(data.length);
    try {
        byte[] buf = new byte[1024];
        while (!compress.finished()) {
            int i = compress.deflate(buf);
            bos.write(buf, 0, i);
        }
        output = bos.toByteArray();
    } catch (Exception e) {
        output = data;
        e.printStackTrace();
    } finally {
        bos.close();
    }
    compress.end();
    return output;
}

一个简单的测试

public static void main(String[] args) throws IOException {
    StringBuilder builder = new StringBuilder();
    for (int i = 0; i < 200; i++) {
        builder.append('a' + (new Random().nextInt() * 26));
    }
    String text = builder.toString();
    byte[] compres = compress(text.getBytes());
    System.out.println(compres.length + " : " + text.getBytes().length);

    String res = uncompress(compres);
    System.out.println("uncompress! \n" + text + "\n" + res);
}

输出结果

1011 : 1974
uncompress! 
1159641073884270587-148914555-876348695-140903655914152858511750740619-504526839109631208315104321891746743931-228808979-1303586499-19431155411964999751-1784318475-954798177-1812907183-831342707-3149322476028964551802022597-269963287-6384200011467670385844411707877038035412670417-1119826115558346219-959513147646693111435818855-32626587-18184494797054550038966016212145089137523302939171183465807867207-5294746515903446057333959811216956465-11772186456902770294071039871896527261-126190055310658640239029635411410052621945318513-1099749933-2044334159884087065-1705740759-1313321287-1408007761-12659778231544522691472523171153203782987609706919936632357801287155512488271333115291-1121944135941979389-179880545175884207196204559-2097788799145839653133892163716038492252042396151523357607329397509-2453452914618397691174247129-542507633-1893723573237001573-84175562119492726191070559557-875056377-1763237523-662399435-170798495-12405874171550890051-1938474621-701626601-1246867757-1138873077164155271023310391435811251050668025181338411-7641844471088518205-1570482881-1690731767-954924683-213656821149494003-544272515-9322840891981997411254437701-183054198720365002211448655569-54030518916444117051191350451-900732825-2072105047160877226512403288354302424851213478975-57604286986096457192173124564975571096304687-213425653510984804314132356831371957625714091709-327695077-182546427-372769058150182636433743131293942149315625331-1010625457741185365-81246881-565236593-1937214707-2090999425-1673181289-1110250756450022071917863643-127217577910228760391902441297-31318475-535669437-1151216791170962161121375401911260706331-1873591233-495048743-8876731551362670289-686442615-6752584831233249861-3467630691547253127-345092207-908370541-1788351797644350365-67770933-4703179231930520693138257968522450375-1171662023-5791753311816936409-1745781765-922801857281665531707439257928142703-367587763829971705455779401438501763-1398546079-606883161-924403277-1617582925-2005411841279115903
1159641073884270587-148914555-876348695-140903655914152858511750740619-504526839109631208315104321891746743931-228808979-1303586499-19431155411964999751-1784318475-954798177-1812907183-831342707-3149322476028964551802022597-269963287-6384200011467670385844411707877038035412670417-1119826115558346219-959513147646693111435818855-32626587-18184494797054550038966016212145089137523302939171183465807867207-5294746515903446057333959811216956465-11772186456902770294071039871896527261-126190055310658640239029635411410052621945318513-1099749933-2044334159884087065-1705740759-1313321287-1408007761-12659778231544522691472523171153203782987609706919936632357801287155512488271333115291-1121944135941979389-179880545175884207196204559-2097788799145839653133892163716038492252042396151523357607329397509-2453452914618397691174247129-542507633-1893723573237001573-84175562119492726191070559557-875056377-1763237523-662399435-170798495-12405874171550890051-1938474621-701626601-1246867757-1138873077164155271023310391435811251050668025181338411-7641844471088518205-1570482881-1690731767-954924683-213656821149494003-544272515-9322840891981997411254437701-183054198720365002211448655569-54030518916444117051191350451-900732825-2072105047160877226512403288354302424851213478975-57604286986096457192173124564975571096304687-213425653510984804314132356831371957625714091709-327695077-182546427-372769058150182636433743131293942149315625331-1010625457741185365-81246881-565236593-1937214707-2090999425-1673181289-1110250756450022071917863643-127217577910228760391902441297-31318475-535669437-1151216791170962161121375401911260706331-1873591233-495048743-8876731551362670289-686442615-6752584831233249861-3467630691547253127-345092207-908370541-1788351797644350365-67770933-4703179231930520693138257968522450375-1171662023-5791753311816936409-1745781765-922801857281665531707439257928142703-367587763829971705455779401438501763-1398546079-606883161-924403277-1617582925-2005411841279115903

2. 注意事项

上面这个运作的还挺好，但在接入使用时，总是提示java.util.zip.DataFormatException: incorrect header check, 因为接受的是第三方传递过来的压缩数据，比较坑爹的是对方就写了个Deflater压缩，然后什么都没有了，那么这个是啥原因呢？

其实看下Deflater的构造方法，发现还可以传一个boolean值(nowrap), 官方说明是

/**
 * Creates a new compressor using the specified compression level.
 * If 'nowrap' is true then the ZLIB header and checksum fields will
 * not be used in order to support the compression format used in
 * both GZIP and PKZIP.
 * @param level the compression level (0-9)
 * @param nowrap if true then use GZIP compatible compression
 */
public Deflater(int level, boolean nowrap) {
    this.level = level;
    this.strategy = DEFAULT_STRATEGY;
    this.zsRef = new ZStreamRef(init(level, DEFAULT_STRATEGY, nowrap));
}

简单来说，就是压缩时，如果nowrap为true，那么解压时也要为true；否则对不上时，就会抛异常

接下来简单对比下两种不同传参的情况，首先更新下工具类

public static String uncompress(byte[] input, boolean nowrap) throws IOException {
    Inflater inflater = new Inflater(nowrap);
    inflater.setInput(input);
    ByteArrayOutputStream baos = new ByteArrayOutputStream(input.length);
    try {
        byte[] buff = new byte[1024];
        while (!inflater.finished()) {
            int count = inflater.inflate(buff);
            baos.write(buff, 0, count);
        }
    } catch (Exception e) {
        e.printStackTrace();
    } finally {
        baos.close();
    }
    inflater.end();
    byte[] output = baos.toByteArray();
    return new String(output);
}

public static byte[] compress(byte[] data, boolean nowrap) throws IOException {
    byte[] output;
    Deflater compress = new Deflater(Deflater.DEFAULT_COMPRESSION, nowrap);

    compress.reset();
    compress.setInput(data);
    compress.finish();
    ByteArrayOutputStream bos = new ByteArrayOutputStream(data.length);
    try {
        byte[] buf = new byte[1024];
        while (!compress.finished()) {
            int i = compress.deflate(buf);
            bos.write(buf, 0, i);
        }
        output = bos.toByteArray();
    } catch (Exception e) {
        output = data;
        e.printStackTrace();
    } finally {
        bos.close();
    }
    compress.end();
    return output;
}

测试如下

public static void main(String[] args) throws IOException {
    StringBuilder builder = new StringBuilder();
    for (int i = 0; i < 1000; i++) {
        builder.append('a' + (new Random().nextInt() * 26));
    }
    String text = builder.toString();
    byte[] compres = compress(text.getBytes(), true);
    System.out.println(compres.length + " : " + text.getBytes().length);
    String res = uncompress(compres, true);
    System.out.println(res.equals(text));


    byte[] compres2 = compress(text.getBytes(), false);
    System.out.println(compres2.length + " : " + text.getBytes().length);
    String res2 = uncompress(compres2, false);
    System.out.println(res2.equals(text));
}

输出结果如下，从大小来看，前者小那么一点点

5086 : 9985
true
5092 : 9985
true

3. 小结

一般来说，jdk自带的压缩与解压，除了方便之外，可能优势并不是那么的大，这里盗一张网上的对比表格

以下来自: [java]序列化框架性能对比（kryo、hessian、java、protostuff）open in new window

优点缺点
kryo速度快，序列化后体积小跨语言支持较复杂
hessian默认支持跨语言较慢
protostuff速度快，基于protobuf需静态编译
Protostuff-Runtime无需静态编译，但序列化前需预先传入schema不支持无默认构造函数的类，反序列化时需用户自己初始化序列化后的对象，其只负责将该对象进行赋值
jdk使用方便，可序列化所有类速度慢，占空间

其次，在使用java的压缩与解压时，需要注意下，nowrap这个参数，需要保持一致，否则会报错

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