Modification log (get the content before and after the field modification)

// User object entity class
@Data
@EqualsAndHashCode(callSuper = false)
@ApiModel(value="user object", description="user table")
public class User {

    @ApiModelProperty(value = "user id")
    private int id;
    @ApiModelProperty(value = "name")
    private String name;
    @ApiModelProperty(value = "age")
    private int age;
    @ApiModelProperty(value = "Address")
    private String address;
}

// User modify log class

@Data
@EqualsAndHashCode(callSuper = false)
@ApiModel(value = "userUpdateLog object", description = "user update log table")
public class UserUpdateLog {

    private static final long serialVersionUID = 1L;

    @ApiModelProperty(value = "主键ID")
    private Long userLogId;


    @ApiModelProperty(value = "Modify Type")
    private String modifyField;

    @ApiModelProperty(value = "Content before modification")
    private String beforeModification;

    @ApiModelProperty(value = "modified content")
    private String afterModification;

}

// Formal code test class
@SpringBootTest(webEnvironment = SpringBootTest.WebEnvironment.DEFINED_PORT)
@RunWith(SpringRunner.class)
public class demo1 {

    /**
     * JDK introspection class library:
     * PropertyDescriptor class: (Property Descriptor)
     * The PropertyDescriptor class means that the JavaBean class exports a property through memory. Main method:
     * 1. getPropertyType(), get the Class object of the property;
     * 2. getReadMethod(), get the method used to read the attribute value;
     * 3. getWriteMethod(), get the method used to write the attribute value;
     * 4. hashCode(), get the hash value of the object;
     * 5. setReadMethod(Method readMethod), set the method used to read the attribute value;
     * 6. setWriteMethod(Method writeMethod), set the method used to write the attribute value
     */
    @Test
    public void test1(){
        User beforeUser=new User();
        beforeUser.setId(1);
        beforeUser.setName("小明");
        beforeUser.setAge(20);
        beforeUser.setAddress("北京");

        User afterUser=new User();
        afterUser.setId(2);
        afterUser.setName("小黑");
        afterUser.setAge(30);
        afterUser.setAddress("上海");
        List<UserUpdateLog> userUpdateLogs = contrastObj(afterUser, beforeUser);
        System.out.println(userUpdateLogs);
    }

    public static List<UserUpdateLog> contrastObj(Object afterObj, Object beforeObj) {
        User afterUser = (User) afterObj;
        User beforeUser = (User) beforeObj;
        List<UserUpdateLog> updateLogList = Lists.newArrayList();
        try {
            Class clazz = afterUser.getClass();
            Field[] fields = afterUser.getClass().getDeclaredFields();
            for (Field field : fields) {
                UserUpdateLog userUpdateLog = new UserUpdateLog();
                if("serialVersionUID".equals(field.getName())){
                    continue;
                }
                //Get the property descriptor of propertyName in the clazz type
                PropertyDescriptor pd = new PropertyDescriptor(field.getName(), clazz);
                // Get the method to read the attribute value getReadMethod()
                Method getMethod = pd.getReadMethod();
                Object o1 = getMethod.invoke(afterUser);
                Object o2 = getMethod.invoke(beforeUser);
                String s1 = o1 == null? "": o1.toString();//Avoid null pointer exception
                String s2 = o2 == null? "": o2.toString();//Avoid null pointer exception
                //Think about the line commented below: there will be bugs, although the program is try catch, the program did not report an error, but the result is not what we want
                // todo my understanding o1 o2 is object type
                //if (!o1.toString().equals(o2.toString())) {
                if (!s1.equals(s2)) {
                    userUpdateLog.setModifyField(field.getAnnotation(ApiModelProperty.class).value());
                    userUpdateLog.setBeforeModification(s2);
                    userUpdateLog.setAfterModification(s1);
                    updateLogList.add(userUpdateLog);
                }
            }
        } catch (Exception e) {
            System.out.println(e.getMessage());
        }
        return updateLogList;
    }

// console output result

[UserUpdateLog(userLogId=null, modifyField=用户id, beforeModification=1, afterModification=2), UserUpdateLog(userLogId=null, modifyField=姓名, beforeModification=小明, afterModification=小黑), UserUpdateLog(userLogId=null, modifyField=年龄, beforeModification=20, afterModification=30), UserUpdateLog(userLogId=null, modifyField=地址, beforeModification=北京, afterModification=上海)]