I was tortured by my colleague's null pointer for a long time, and finally learned how to deal with null pointer

A fan has been employed for so long , In any case, I wouldn't expect to be tortured to death by a null pointer returned by an interface written by my colleagues , Tortured to death , But I don't know why , Have you ever had such an experience ？

NullPointerException

The title is eye-catching , To tell you , This null pointer is abnormal , Tell the truth , Many of them are easy to solve in the project , But sometimes the cause of problems is something you can't think of , It's like this .

The front-end code is as follows ：

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        var setting = {
        
                url:"findFileById",
        
                data:{
        
                    id:id
        
                },
        
                success:function (data) {
        
                    console.log(data);
        
                },
        
                error:function (data) {
        
                    console.log(" Abnormal query file ")
        
                }
        
            }
        
ajax(setting);
        

        
ajax Here is just a package 
        

        
function ajax(setting) {
        
    $.ajax({
        
        type:"post",
        
        url:setting.url+".do",
        
        dataType:setting.dataType||"json",
        
        contentType:"application/json;utf-8",
        
        data:JSON.stringify(setting.data)||{},
        
        async:setting.async,
        
        success:function (data) {
        
            setting.success(data);
        
        },
        
        error:function (data) {
        
            setting.error(" Interface error , Please try again ");
        
        }
        
    })
       
       

        
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The background business processing is as follows ：

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        @PostMapping("findFileById")
        
@ResponseBody
        
public File findFileById(HttpServletRequest request, HttpServletResponse response, @RequestBody Map
        <
        String,Object
        > map){
        
    return deliverFileService.findFileById(request,map);
        
}
       
       

        
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I'm sure you'll say , You can't do such a simple thing , What do you eat, fan , There is a problem with every query file , As a matter of fact , In the code, my colleagues did not completely deal with the problem of null value , The result has been ajax There is “ Interface error , Please try again ” Error of .

The problem is that he doesn't process empty data , And directly returned to me , This kind of problem is also very strange , Many times, it is not necessary to deal with empty data to prevent NULL Is it abnormal ？ And ah fan also found him at the first time , He said no problem , Call normally from him , I was embarrassed at that time , The parameters I passed you are ok , If the query data is empty , There should be a prompt . So ah fan can only simply modify his code , Turned into

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        @PostMapping("findFileById")
        
@ResponseBody
        
public File findFileById(HttpServletRequest request, HttpServletResponse response, @RequestBody Map
        <
        String,Object
        > map){
        
    return deliverFileService.findFileById(request,map)!= null ?deliverFileService.findFileById(request,map) : new ; new DeliverFile();
        
}
       
       

        
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A fan can't make too big changes to him , It can only be called here if it is null When , Just return me an empty object , If not , Just return the queried data to me .

Now let's talk about how to deal with our null value , Otherwise, if you write a data interface in the future , Call others , If the call is an empty string, it's just , But if it looks like null This kind of thing that is not handled , Then you will be despised by others .

How to deal with null pointer exceptions

When will it appear NullPointerException？

We all know NullPointerException It's inheritance RuntimeException Of , That is, the abnormal information will appear when running , When we write code , If the code is running , When the object we use is not initialized , Or when it is empty , There will be an exception of null pointer , And this anomaly is what we feel most Low Of , The most unlikely exception , But often because of their own inattention , And that's what happened .

In fact, there are too many ways , And many times we don't pay attention to this matter , For example, object , Empty operation , But if you judge empty when using each object , Then your code will really appear ：

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        if(a!=null){
        
    if(b!=null){
        
        if(c!=null){
        
            ....
        
        }
        
    }
        
}
       
       

        
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When you see this code , The first feeling is whether you directly want to pull this friend over and beat him , If you write too much , People are going crazy , Especially the secondary maintenance personnel .

In fact, although this method is stupid , But it's also a habit , Sentenced to empty , Functionally , Surely there won't be a lot of trouble , But such a null value is also very painful , Then let's deal with him .

1. Let's not talk about this. Just judge whether the object is empty .

the second , Just compare equals Method time , This is our writing habit many times

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        if(text.equals("xxxxx")){
        

        
}
       
       

        
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In fact, there is no problem with this comparison , But have you ever thought about it , If you say your text It's empty ？ When you compare, you make mistakes ？ And once an interviewer asked me , Why write the known string in front of the written test question , Maybe it was just a habit at that time , But later I found it was really useful .

You change to ：

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        if("xxxxx".equals(text)){
        

        
}
       
       

        
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The error of null pointer will be avoided , What a good habit, isn't it ？

Third , We are also in Java8 Features provided inside Optional

ofNullable, Namely Optional Provided in , Pass the parameters we need , You can judge whether it is empty .

And for sets , You can use the method modified before , Judge whether it is null, If it is null, Then we must return an empty object , Or an empty set , For those who call your interface later , Also very friendly .

I know many people will say , Then I'll write a comment on the interface , The value returned by the query may be empty , Please call carefully , Although you prompted the question , But you are not solving the problem , Equivalent to , You threw out all the anomalies , Instead of dealing with him .

We can also use Java8 Provided in Optional , Like this

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        Optional
        <
        Product
        >getProductOptional(String id)
       
       

        
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This is the time , When our caller knows there is Optional In the presence of , Naturally understand .

About handling null, Do you have any other good ways ？