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HBase Filter 过滤器之 Comparator 原理及源码学习
2020-06-23 16:33:54

前言:上篇文章HBase Filter 过滤器概述对HBase过滤器的组成及其家谱进行简单介绍,本篇文章主要对HBase过滤器之比较器作一个补充介绍,也算是HBase Filter学习的必备低阶魂技吧。本篇文中源码基于HBase 1.1.2.2.6.5.0-292 HDP版本。

HBase所有的比较器实现类都继承于父类ByteArrayComparable,而ByteArrayComparable又实现了Comparable接口;不同功能的比较器差别在于对父类compareTo()方法的重写逻辑不同。

下面分别对HBase Filter默认实现的七大比较器一一进行介绍。

1. BinaryComparator

介绍:二进制比较器,用于按字典顺序比较指定字节数组。

先看一个小例子:

public class BinaryComparatorDemo {

    public static void main(String[] args) {

        BinaryComparator bc = new BinaryComparator(Bytes.toBytes("bbb"));

        int code1 = bc.compareTo(Bytes.toBytes("bbb"), 0, 3);
        System.out.println(code1); // 0
        int code2 = bc.compareTo(Bytes.toBytes("aaa"), 0, 3);
        System.out.println(code2); // 1
        int code3 = bc.compareTo(Bytes.toBytes("ccc"), 0, 3);
        System.out.println(code3); // -1
        int code4 = bc.compareTo(Bytes.toBytes("bbf"), 0, 3);
        System.out.println(code4); // -4
        int code5 = bc.compareTo(Bytes.toBytes("bbbedf"), 0, 6);
        System.out.println(code5); // -3
    }
}

不难看出,该比较器的比较规则如下:

  • 两个字符串首字母不同,则该方法返回首字母的asc码的差值
  • 参与比较的两个字符串如果首字符相同,则比较下一个字符,直到有不同的为止,返回该不同的字符的asc码差值
  • 两个字符串不一样长,可以参与比较的字符又完全一样,则返回两个字符串的长度差值

看一下以上规则对应其compareTo()方法的源码实现: 实现一:

static enum UnsafeComparer implements Bytes.Comparer<byte[]> {
INSTANCE;
....
public int compareTo(byte[] buffer1, int offset1, int length1, byte[] buffer2, int offset2, int length2) {
    if (buffer1 == buffer2 && offset1 == offset2 && length1 == length2) {
        return 0;
    } else {
        int minLength = Math.min(length1, length2);
        int minWords = minLength / 8;
        long offset1Adj = (long)(offset1 + BYTE_ARRAY_BASE_OFFSET);
        long offset2Adj = (long)(offset2 + BYTE_ARRAY_BASE_OFFSET);
        int j = minWords << 3;

        int offset;
        for(offset = 0; offset < j; offset += 8) {
            long lw = theUnsafe.getLong(buffer1, offset1Adj + (long)offset);
            long rw = theUnsafe.getLong(buffer2, offset2Adj + (long)offset);
            long diff = lw ^ rw;
            if (diff != 0L) {
                return lessThanUnsignedLong(lw, rw) ? -1 : 1;
            }
        }

        offset = j;
        int b;
        int a;
        if (minLength - j >= 4) {
            a = theUnsafe.getInt(buffer1, offset1Adj + (long)j);
            b = theUnsafe.getInt(buffer2, offset2Adj + (long)j);
            if (a != b) {
                return lessThanUnsignedInt(a, b) ? -1 : 1;
            }

            offset = j + 4;
        }

        if (minLength - offset >= 2) {
            short sl = theUnsafe.getShort(buffer1, offset1Adj + (long)offset);
            short sr = theUnsafe.getShort(buffer2, offset2Adj + (long)offset);
            if (sl != sr) {
                return lessThanUnsignedShort(sl, sr) ? -1 : 1;
            }

            offset += 2;
        }

        if (minLength - offset == 1) {
            a = buffer1[offset1 + offset] & 255;
            b = buffer2[offset2 + offset] & 255;
            if (a != b) {
                return a - b;
            }
        }

        return length1 - length2;
    }
}

实现二:

static enum PureJavaComparer implements Bytes.Comparer<byte[]> {
    INSTANCE;

    private PureJavaComparer() {
    }

    public int compareTo(byte[] buffer1, int offset1, int length1, byte[] buffer2, int offset2, int length2) {
        if (buffer1 == buffer2 && offset1 == offset2 && length1 == length2) {
            return 0;
        } else {
            int end1 = offset1 + length1;
            int end2 = offset2 + length2;
            int i = offset1;

            for(int j = offset2; i < end1 && j < end2; ++j) {
                int a = buffer1[i] & 255;
                int b = buffer2[j] & 255;
                if (a != b) {
                    return a - b;
                }

                ++i;
            }

            return length1 - length2;
        }
    }
}

实现一是对实现二的一个优化,都引自Bytes类,HBase优先执行实现一方案,如果有异常再执行实现二方案。如下:

public static int compareTo(byte[] buffer1, int offset1, int length1, byte[] buffer2, int offset2, int length2) {
    return Bytes.LexicographicalComparerHolder.BEST_COMPARER.compareTo(buffer1, offset1, length1, buffer2, offset2, length2);
}
...
...

static final String UNSAFE_COMPARER_NAME = Bytes.LexicographicalComparerHolder.class.getName() + "$UnsafeComparer";
static final Bytes.Comparer<byte[]> BEST_COMPARER = getBestComparer();
static Bytes.Comparer<byte[]> getBestComparer() {
    try {
        Class<?> theClass = Class.forName(UNSAFE_COMPARER_NAME);
        Bytes.Comparer<byte[]> comparer = (Bytes.Comparer)theClass.getEnumConstants()[0];
        return comparer;
    } catch (Throwable var2) {
        return Bytes.lexicographicalComparerJavaImpl();
    }
}

2. BinaryPrefixComparator

介绍:二进制比较器,只比较前缀是否与指定字节数组相同。

先看一个小例子:

public class BinaryPrefixComparatorDemo {

    public static void main(String[] args) {

        BinaryPrefixComparator bc = new BinaryPrefixComparator(Bytes.toBytes("b"));

        int code1 = bc.compareTo(Bytes.toBytes("bbb"), 0, 3);
        System.out.println(code1); // 0
        int code2 = bc.compareTo(Bytes.toBytes("aaa"), 0, 3);
        System.out.println(code2); // 1
        int code3 = bc.compareTo(Bytes.toBytes("ccc"), 0, 3);
        System.out.println(code3); // -1
        int code4 = bc.compareTo(Bytes.toBytes("bbf"), 0, 3);
        System.out.println(code4); // 0
        int code5 = bc.compareTo(Bytes.toBytes("bbbedf"), 0, 6);
        System.out.println(code5); // 0
        int code6 = bc.compareTo(Bytes.toBytes("ebbedf"), 0, 6);
        System.out.println(code6); // -3
    }
}

该比较器只是基于BinaryComparator比较器稍作更改而已,以下代码一目了然:

public int compareTo(byte[] value, int offset, int length) {
    return Bytes.compareTo(this.value, 0, this.value.length, value, offset, this.value.length <= length ? this.value.length : length);
}

看一下同BinaryComparator方法的异同:

public int compareTo(byte[] value, int offset, int length) {
    return Bytes.compareTo(this.value, 0, this.value.length, value, offset, length);
}

区别只在于后一个传参,即length=min(this.value.length,value.length),取小。这样在后面的字节逐位比较时,即只需比较min length次。

3. BitComparator

介绍:位比价器,通过BitwiseOp提供的AND(与)、OR(或)、NOT(非)进行比较。返回结果要么为1要么为0,仅支持 EQUAL 和非 EQUAL。

先看一个小例子:

public class BitComparatorDemo {

    public static void main(String[] args) {

        // 长度相同按位或比较:由低位起逐位比较,每一位按位或比较都为0,则返回1,否则返回0。
        BitComparator bc1 = new BitComparator(new byte[]{0,0,0,0}, BitComparator.BitwiseOp.OR);
        int i = bc1.compareTo(new byte[]{0,0,0,0}, 0, 4);
        System.out.println(i); // 1
        // 长度相同按位与比较:由低位起逐位比较,每一位按位与比较都为0,则返回1,否则返回0。
        BitComparator bc2 = new BitComparator(new byte[]{1,0,1,0}, BitComparator.BitwiseOp.AND);
        int j = bc2.compareTo(new byte[]{0,1,0,1}, 0, 4);
        System.out.println(j); // 1
        // 长度相同按位异或比较:由低位起逐位比较,每一位按位异或比较都为0,则返回1,否则返回0。
        BitComparator bc3 = new BitComparator(new byte[]{1,0,1,0}, BitComparator.BitwiseOp.XOR);
        int x = bc3.compareTo(new byte[]{1,0,1,0}, 0, 4);
        System.out.println(x); // 1
        // 长度不同,返回1,否则按位比较
        BitComparator bc4 = new BitComparator(new byte[]{1,0,1,0}, BitComparator.BitwiseOp.XOR);
        int y = bc4.compareTo(new byte[]{1,0,1}, 0, 3);
        System.out.println(y); // 1
    }
}

上述注释阐述的规则,对应以下代码: ··· public int compareTo(byte[] value, int offset, int length) { if (length != this.value.length) { return 1; } else { int b = 0;

    for(int i = length - 1; i >= 0 && b == 0; --i) {
        switch(this.bitOperator) {
        case AND:
            b = this.value[i] & value[i + offset] & 255;
            break;
        case OR:
            b = (this.value[i] | value[i + offset]) & 255;
            break;
        case XOR:
            b = (this.value[i] ^ value[i + offset]) & 255;
        }
    }

    return b == 0 ? 1 : 0;
}

} ··· 核心思想就是:由低位起逐位比较,直到b!=0退出循环。

4. LongComparator

介绍:Long 型专用比较器,返回值:0 -1 1。上篇概述没有提到,这里补上。

先看一个小例子:

public class LongComparatorDemo {

    public static void main(String[] args) {
        LongComparator longComparator = new LongComparator(1000L);
        int i = longComparator.compareTo(Bytes.toBytes(1000L), 0, 8);
        System.out.println(i); // 0
        int i2 = longComparator.compareTo(Bytes.toBytes(1001L), 0, 8);
        System.out.println(i2); // -1
        int i3 = longComparator.compareTo(Bytes.toBytes(998L), 0, 8);
        System.out.println(i3); // 1
    }
}

这个比较器实现相当简单,不多说了,如下:

public int compareTo(byte[] value, int offset, int length) {
    Long that = Bytes.toLong(value, offset, length);
    return this.longValue.compareTo(that);
}

5. NullComparatorDemo

介绍:控制比较式,判断当前值是不是为null。是null返回0,不是null返回1,仅支持 EQUAL 和非 EQUAL。

先看一个小例子:

public class NullComparatorDemo {

    public static void main(String[] args) {
        NullComparator nc = new NullComparator();
        int i1 = nc.compareTo(Bytes.toBytes("abc"));
        int i2 = nc.compareTo(Bytes.toBytes(""));
        int i3 = nc.compareTo(null);
        System.out.println(i1); // 1
        System.out.println(i2); // 1
        System.out.println(i3); // 0
    }
}

这个比较器实现相当简单,不多说了,如下:

public int compareTo(byte[] value) {
    return value != null ? 1 : 0;
}

6. RegexStringComparator

介绍:提供一个正则的比较器,支持正则表达式的值比较,仅支持 EQUAL 和非 EQUAL。匹配成功返回0,匹配失败返回1。

先看一个小例子:

public class RegexStringComparatorDemo {

    public static void main(String[] args) {
        RegexStringComparator rsc = new RegexStringComparator("abc");
        int abc = rsc.compareTo(Bytes.toBytes("abcd"), 0, 3);
        System.out.println(abc); // 0
        int bcd = rsc.compareTo(Bytes.toBytes("bcd"), 0, 3);
        System.out.println(bcd); // 1

        String check = "^([a-z0-9A-Z]+[-|\\.]?)+[a-z0-9A-Z]@([a-z0-9A-Z]+(-[a-z0-9A-Z]+)?\\.)+[a-zA-Z]{2,}$";
        RegexStringComparator rsc2 = new RegexStringComparator(check);
        int code = rsc2.compareTo(Bytes.toBytes("zpb@163.com"), 0, "zpb@163.com".length());
        System.out.println(code); // 0
        int code2 = rsc2.compareTo(Bytes.toBytes("zpb#163.com"), 0, "zpb#163.com".length());
        System.out.println(code2); // 1
    }
}

其compareTo()方法有两种引擎实现,对应两套正则匹配规则,分别是JAVA版和JONI版(面向JRuby),默认为RegexStringComparator.EngineType.JAVA。如下:

public int compareTo(byte[] value, int offset, int length) {
    return this.engine.compareTo(value, offset, length);
}

public static enum EngineType {
    JAVA,
    JONI;

    private EngineType() {
    }
}

具体实现都很简单,都是调用正则语法匹配。以下是JAVA EngineType 实现:

public int compareTo(byte[] value, int offset, int length) {
    String tmp;
    if (length < value.length / 2) {
        tmp = new String(Arrays.copyOfRange(value, offset, offset + length), this.charset);
    } else {
        tmp = new String(value, offset, length, this.charset);
    }

    return this.pattern.matcher(tmp).find() ? 0 : 1;
}

JONI EngineType 实现:

public int compareTo(byte[] value, int offset, int length) {
    Matcher m = this.pattern.matcher(value);
    return m.search(offset, length, this.pattern.getOptions()) < 0 ? 1 : 0;
}

都很容易理解,不多说了。

7. SubstringComparator

介绍:判断提供的子串是否出现在value中,并且不区分大小写。包含字串返回0,不包含返回1,仅支持 EQUAL 和非 EQUAL。

先看一个小例子:

public class SubstringComparatorDemo {

    public static void main(String[] args) {
        String value = "aslfjllkabcxxljsl";
        SubstringComparator sc = new SubstringComparator("abc");
        int i = sc.compareTo(Bytes.toBytes(value), 0, value.length());
        System.out.println(i); // 0

        SubstringComparator sc2 = new SubstringComparator("abd");
        int i2 = sc2.compareTo(Bytes.toBytes(value), 0, value.length());
        System.out.println(i2); // 1

        SubstringComparator sc3 = new SubstringComparator("ABC");
        int i3 = sc3.compareTo(Bytes.toBytes(value), 0, value.length());
        System.out.println(i3); // 0
    }
}

这个比较器实现也相当简单,不多说了,如下:

public int compareTo(byte[] value, int offset, int length) {
    return Bytes.toString(value, offset, length).toLowerCase().contains(this.substr) ? 0 : 1;
}

到此,七种比较器就介绍完了。如果对源码不敢兴趣,也建议一定要看看文中的小例子,熟悉下每种比较器的构造函数及结果输出。后续在使用HBase过滤器的过程中,会经常用到。当然除了这七种比较器,大家也可以自定义比较器。

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