Online Incident Review
Some time ago, a very simple function was added. When I went online at night, reviewI thought of the company's hard-working and enterprising values and temporarily added a log log. I felt that there was basically no problem with a simple log line. Rolled back the code, found the problem, deleted the code that added the log, and went online again.
Scenario restoration
defines a
CountryDTO
public class CountryDTO {
private String country;
public void setCountry(String country) {
this.country = country;
}
public String getCountry() {
return this.country;
}
public Boolean isChinaName() {
return this.country.equals("中国");
}
}
复制代码define test class
FastJonTest
public class FastJonTest {
@Test
public void testSerialize() {
CountryDTO countryDTO = new CountryDTO();
String str = JSON.toJSONString(countryDTO);
System.out.println(str);
}
}
复制代码Runtime 空指针error: From the error message, it can be seen that the
isChinaName()method . At this time, the this.countryvariable is empty, then the problem is:
- Why is serialization performed
isChinaName()? - By extension, what methods will be executed during the serialization process?
Source code analysis
Observe the stack information of the
call chain through debug. In the call chain, a class
ASMSerializer_1_CountryDTO.writeis dynamically generated FastJsonusing technology .asmASMSerializer_1_CountryDTO
One of the usage scenarios of asm technology is to replace
javareflection by dynamically generating classes to avoid reflection overhead during repeated execution
JavaBeanSerizlier serialization principle
It can be seen from the figure below that in the process of serialization, JavaBeanSerializerthe method of the class is mainly called write(). And
JavaBeanSerializeris mainly obtained through the getObjectWriter()method , and by getObjectWriter()debugging the execution process, find the more critical com.alibaba.fastjson.serializer.SerializeConfig#createJavaBeanSerializermethods, and then findcom.alibaba.fastjson.util.TypeUtils#computeGetters
public static List<FieldInfo> computeGetters(Class<?> clazz, //
JSONType jsonType, //
Map<String,String> aliasMap, //
Map<String,Field> fieldCacheMap, //
boolean sorted, //
PropertyNamingStrategy propertyNamingStrategy //
){
//省略部分代码....
Method[] methods = clazz.getMethods();
for(Method method : methods){
//省略部分代码...
if(method.getReturnType().equals(Void.TYPE)){
continue;
}
if(method.getParameterTypes().length != 0){
continue;
}
//省略部分代码...
JSONField annotation = TypeUtils.getAnnotation(method, JSONField.class);
//省略部分代码...
if(annotation != null){
if(!annotation.serialize()){
continue;
}
if(annotation.name().length() != 0){
//省略部分代码...
}
}
if(methodName.startsWith("get")){
//省略部分代码...
}
if(methodName.startsWith("is")){
//省略部分代码...
}
}
}
复制代码From the code, it can be roughly divided into three cases:
@JSONField(.serialize = false, name = "xxx")annotationgetXxx(): method starting with getisXxx(): methods starting with is
Serialization Flowchart
sample code
/**
* case1: @JSONField(serialize = false)
* case2: getXxx()返回值为void
* case3: isXxx()返回值不等于布尔类型
* case4: @JSONType(ignores = "xxx")
*/
@JSONType(ignores = "otherName")
public class CountryDTO {
private String country;
public void setCountry(String country) {
this.country = country;
}
public String getCountry() {
return this.country;
}
public static void queryCountryList() {
System.out.println("queryCountryList()执行!!");
}
public Boolean isChinaName() {
System.out.println("isChinaName()执行!!");
return true;
}
public String getEnglishName() {
System.out.println("getEnglishName()执行!!");
return "lucy";
}
public String getOtherName() {
System.out.println("getOtherName()执行!!");
return "lucy";
}
/**
* case1: @JSONField(serialize = false)
*/
@JSONField(serialize = false)
public String getEnglishName2() {
System.out.println("getEnglishName2()执行!!");
return "lucy";
}
/**
* case2: getXxx()返回值为void
*/
public void getEnglishName3() {
System.out.println("getEnglishName3()执行!!");
}
/**
* case3: isXxx()返回值不等于布尔类型
*/
public String isChinaName2() {
System.out.println("isChinaName2()执行!!");
return "isChinaName2";
}
}
复制代码The running result is:
isChinaName()执行!!
getEnglishName()执行!!
{"chinaName":true,"englishName":"lucy"}
复制代码code specification
可以看出来序列化的规则还是很多的，比如有时需要关注返回值，有时需要关注参数个数，有时需要关注@JSONType注解，有时需要关注@JSONField注解；当一个事物的判别方式有多种的时候，由于团队人员掌握知识点的程度不一样，这个方差很容易导致代码问题，所以尽量有一种推荐方案。 这里推荐使用@JSONField(serialize = false)来显式的标注方法不参与序列化，下面是使用推荐方案后的代码，是不是一眼就能看出来哪些方法不需要参与序列化了。
public class CountryDTO {
private String country;
public void setCountry(String country) {
this.country = country;
}
public String getCountry() {
return this.country;
}
@JSONField(serialize = false)
public static void queryCountryList() {
System.out.println("queryCountryList()执行!!");
}
public Boolean isChinaName() {
System.out.println("isChinaName()执行!!");
return true;
}
public String getEnglishName() {
System.out.println("getEnglishName()执行!!");
return "lucy";
}
@JSONField(serialize = false)
public String getOtherName() {
System.out.println("getOtherName()执行!!");
return "lucy";
}
@JSONField(serialize = false)
public String getEnglishName2() {
System.out.println("getEnglishName2()执行!!");
return "lucy";
}
@JSONField(serialize = false)
public void getEnglishName3() {
System.out.println("getEnglishName3()执行!!");
}
@JSONField(serialize = false)
public String isChinaName2() {
System.out.println("isChinaName2()执行!!");
return "isChinaName2";
}
}
复制代码三个频率高的序列化的情况
以上流程基本遵循 发现问题 --> 原理分析 --> 解决问题 --> 升华(编程规范)。
- 围绕业务上：解决问题 -> 如何选择一种好的额解决方案 -> 好的解决方式如何扩展n个系统应用；
- 围绕技术上：解决单个问题，顺着单个问题掌握这条线上的原理。