fastjson序列化和反序列化理解
json序列化直接根据get 和set方法进行序列化
json反序列化则有以下几个步骤
-
没有构造函数的类，java中有默认无参构造函数，此时反序列化会根据get set方法的名称进行属性赋值，使用没问题
-
当类中存在一个自定义有参构造函数的时候，此时java默认无参构造函数就没有了，此时反序列化是以有参构造函数的参数名称进行注入的，与类型无关
-
当类中存在多个自定义有参构造函数的时候，此时反序列化将以参数长的为优先进行反序列化
-
当类中存在多个自定义有参构造函数，且参数个数一致，参数类型不一致，此时反序列化将以构造函数的先后顺序进行
针对以上四种情况，以代码举例如下：
当只有一个有参构造函数的时候
private String name;
private String education;
public Student(String name) {
this.name = name;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String getEducation() {
return education;
}
public void setEducation(String education) {
this.education = education;
}
@Override
public String toString() {
return
"Student{" +
" name='" + name + '\'' +
", education='" + education + '\'' +
'}';
}
测试类如下：
Student student = new Student("张三");
student.setEducation("大学");
String jsonStr = JSON.toJSONString(student);
Student student1 = JSON.parseObject(jsonStr,Student.class);
System.out.println(student1);
输出结果如下，尽管设置了education的值，但是反序列化的时候，由于构造方法里没有这个字段，所以也不会赋值：
{"name":"张三","education":"大学"}
Student{ name='张三',education='null'}
当同时存在一个无参构造函数和一个有参构造函数的时候
private String name;
private String education;
public Student(String name) {
this.name = name;
}
public Student() {
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String getEducation() {
return education;
}
public void setEducation(String education) {
this.education = education;
}
@Override
public String toString() {
return
"Student{" +
" name='" + name + '\'' +
", education='" + education + '\'' +
'}';
}
测试类如下：
Student student = new Student("张三");
student.setEducation("大学");
String jsonStr = JSON.toJSONString(student);
Student student1 = JSON.parseObject(jsonStr,Student.class);
System.out.println(student1);
输出结果如下，两个字段数据都没有丢失：
{"name":"张三","education":"大学"}
Student{name='张三', education='大学'}
当存在多个构造函数的时候
private String name;
private String education;
public Student(String name) {
this.name = name;
}
public Student(String name, String education) {
this.name = name;
this.education = education;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String getEducation() {
return education;
}
public void setEducation(String education) {
this.education = education;
}
@Override
public String toString() {
return
"Student{" +
" name='" + name + '\'' +
", education='" + education + '\'' +
'}';
}
测试类如下：
Student student = new Student("张三");
student.setEducation("大学");
String jsonStr = JSON.toJSONString(student);
Student student1 = JSON.parseObject(jsonStr,Student.class);
System.out.println(student1);
输出结果如下，由于存在一个更长的构造方法，以更长的为准，两个字段数据都不会丢失：
{"name":"张三","education":"大学"}
Student{name='张三', education='大学'}
当存在多个相同个数的构造函数时
private String name;
private String education;
public Student(int name) {
this.name = "name";
}
public Student(String name) {
this.name = name;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String getEducation() {
return education;
}
public void setEducation(String education) {
this.education = education;
}
@Override
public String toString() {
return
"Student{" +
" name='" + name + '\'' +
", education='" + education + '\'' +
'}';
}
测试类如下：
Student student = new Student("张三");
student.setEducation("大学");
String jsonStr = JSON.toJSONString(student);
Student student1 = JSON.parseObject(jsonStr,Student.class);
System.out.println(student1);
输出结果如下，由于整型在前，字符串的构造函数在后，优先以在前的函数进行反序列化，就会报错：
Exception in thread "main" com.alibaba.fastjson.JSONException: parseInt error, field : name
at com.alibaba.fastjson.serializer.IntegerCodec.deserialze(IntegerCodec.java:99)
at com.alibaba.fastjson.parser.deserializer.DefaultFieldDeserializer.parseField(DefaultFieldDeserializer.java:86)
at com.alibaba.fastjson.parser.deserializer.JavaBeanDeserializer.parseField(JavaBeanDeserializer.java:1078)
at com.alibaba.fastjson.parser.deserializer.JavaBeanDeserializer.deserialze(JavaBeanDeserializer.java:773)
at com.alibaba.fastjson.parser.deserializer.JavaBeanDeserializer.deserialze(JavaBeanDeserializer.java:271)
at com.alibaba.fastjson.parser.deserializer.JavaBeanDeserializer.deserialze(JavaBeanDeserializer.java:267)
at com.alibaba.fastjson.parser.DefaultJSONParser.parseObject(DefaultJSONParser.java:661)
at com.alibaba.fastjson.JSON.parseObject(JSON.java:365)
at com.alibaba.fastjson.JSON.parseObject(JSON.java:269)
at com.alibaba.fastjson.JSON.parseObject(JSON.java:488)
at Main.main(Main.java:39)
Caused by: java.lang.NumberFormatException: For input string: "张三"
at java.lang.NumberFormatException.forInputString(NumberFormatException.java:65)
at java.lang.Integer.parseInt(Integer.java:580)
at java.lang.Integer.parseInt(Integer.java:615)
at com.alibaba.fastjson.util.TypeUtils.castToInt(TypeUtils.java:588)
at com.alibaba.fastjson.serializer.IntegerCodec.deserialze(IntegerCodec.java:95)
... 10 more