fastjson反序列化机制
fastjson提供了智能匹配的规则，下面写法会自动映射
op_id->opid->ipId
也就是说就算json字符串是’op_id’，那java变量也可以用opid或者opId，然后也可以获取相应的数据。
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| public class Runme {
static int ONE_DAY_SECONDS = 24 * 60 * 60 * 1000;
public static void main(String[] args) {
String json = "{\"op-id\":1000}";
Mo mo = JSON.parseObject(json, Mo.class);
System.out.println(mo.getOpId());
}
public static class Mo {
private String opId;
public String getOpId() {
return opId;
}
public void setOpId(String opId) {
this.opId = opId;
}
}
}
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原理分析
那fastjson是怎么做到的呢？
看了下源代码
https://github.com/alibaba/fastjson
发现它的逻辑如下：
文件：src/main/java/com/alibaba/fastjson/parser/deserializer/JavaBeanDeserializer.java
方法: smartMatch(String key, int[] setFlags)
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| public FieldDeserializer smartMatch(String key, int[] setFlags) {
if (key == null) {
return null;
}
FieldDeserializer fieldDeserializer = getFieldDeserializer(key, setFlags);
if (fieldDeserializer == null) {
long smartKeyHash = TypeUtils.fnv1a_64_lower(key);
if (this.smartMatchHashArray == null) {
long[] hashArray = new long[sortedFieldDeserializers.length];
for (int i = 0; i < sortedFieldDeserializers.length; i++) {
hashArray[i] = TypeUtils.fnv1a_64_lower(sortedFieldDeserializers[i].fieldInfo.name);
}
Arrays.sort(hashArray);
this.smartMatchHashArray = hashArray;
}
int pos = Arrays.binarySearch(smartMatchHashArray, smartKeyHash);
boolean is = false;
if (pos < 0 && (is = key.startsWith("is"))) {
smartKeyHash = TypeUtils.fnv1a_64_lower(key.substring(2));
pos = Arrays.binarySearch(smartMatchHashArray, smartKeyHash);
}
if (pos >= 0) {
if (smartMatchHashArrayMapping == null) {
short[] mapping = new short[smartMatchHashArray.length];
Arrays.fill(mapping, (short) -1);
for (int i = 0; i < sortedFieldDeserializers.length; i++) {
int p = Arrays.binarySearch(smartMatchHashArray, TypeUtils.fnv1a_64_lower(sortedFieldDeserializers[i].fieldInfo.name));
if (p >= 0) {
mapping[p] = (short) i;
}
}
smartMatchHashArrayMapping = mapping;
}
int deserIndex = smartMatchHashArrayMapping[pos];
if (deserIndex != -1) {
if (!isSetFlag(deserIndex, setFlags)) {
fieldDeserializer = sortedFieldDeserializers[deserIndex];
}
}
}
if (fieldDeserializer != null) {
FieldInfo fieldInfo = fieldDeserializer.fieldInfo;
if ((fieldInfo.parserFeatures & Feature.DisableFieldSmartMatch.mask) != 0) {
return null;
}
Class fieldClass = fieldInfo.fieldClass;
if (is && (fieldClass != boolean.class && fieldClass != Boolean.class)) {
fieldDeserializer = null;
}
}
}
return fieldDeserializer;
}
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它里面有个重要的地方就是调用TypeUtils.fnv1a_64_lower(String)方法，分别计算传入的key(op_id)和定义的java成员变量opId，然后计算他们是否匹配。
如果匹配的话，就会覆盖。
所以，关键就在于TypeUtils.fnv1a_64_lower(String)方法实现，如下：
这个方法就是如果是’_’或者’-‘，那么就忽略，也就是如果是op_id，那么就会变成opid。
如果是大写，那么就转换成小写，也就是opId，就会变成opid。
所以op-id或者op_id，都可以匹配opId或者opid
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| public static long fnv1a_64_lower(String key){
long hashCode = 0xcbf29ce484222325L;
for(int i = 0; i < key.length(); ++i){
char ch = key.charAt(i);
if(ch == '_' || ch == '-'){
continue;
}
if(ch >= 'A' && ch <= 'Z'){
ch = (char) (ch + 32);
}
hashCode ^= ch;
hashCode *= 0x100000001b3L;
}
return hashCode;
}
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去除json中不规范的引号和空格
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| s = StringEscapeUtils.unescapeJson(s); \\反转义
jsonarray.getObject(0, String.class); \\取json数组的第一个元素，并且会反转义字符串
s = s.replaceAll("\"[\\s]+", "\""); \\ 去除引号后的多余空白字符
s = s.replaceAll("[\\s]+\"", "\""); \\ 去除引号前的多余空白字符
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