primitive or wrapper type of fieds defined in entity

whether using primitive or wrapper type of fieds defined in entity as per your data model and DB side. if the corresponding column in DB allows null, you should use wrapper type like Short, Integer and Long instead of short, int and long, to avoid NullPointerException occurs.

Specifically, if you have a private int age in your entity;

public setAge(int age){
    this.age = age;
}

and this field has a column in DB allows null, thus if search from DB, null cannot be transformed to a primitive data, thus will get NullPointerException.

So use wrapper type instead.

Three ways solving Spring Boot Cannot determine embedded database driver class for database type NONE

If you don’t have a DataSource configured for your spring boot application, when you run spring boot application, it tries to configure the DataSource and throws this error message when there is no configuration provided.

We have three ways to slove this:

1) If you don't need any data source, just exclude it as below:

@SpringBootApplication
@EnableAutoConfiguration(exclude={DataSourceAutoConfiguration.class})
public class SpringBootDemoApplication { }

2) If you need ds just for test purpose, say using an embedded DB like HSqldb, just add the dependency in your pom or yml file:

<dependency>

 <groupId>org.hsqldb</groupId>

 <artifactId>hsqldb</artifactId>

 <scope>runtime</scope>

</dependency>

3) Or you want to have your own external DB configuration, you need to provided DS information in spring boot configuration file, generally add below into application.properties is fine:

spring.datasource.url=xxx

spring.datasource.* is the default prefix for spring boot data source configuration, if you use other prefix, you may need add your own ds configuration file.

access-control-allow-origin

When do development, especially front end and back end are separated in different projects, it is easy to get  access-control-allow-origin error when call webservices.

For this, we have some solutions:

1) For front end, we can add some proxy logic to redirect front end HTTP request through proxy, for instance, our front end application runs on http://localhost:3000, and back end application on http://localhost:8000, if front end make a service call to back end, say /api/v1/students, the call will proxyed to http://localhost:8000/api/v1/students, not http://localhost:3000/api/v1/students, thus avoiding access-control-allow-origin error from the browser. for instance, if you use gulp serve, in server.js file, you can use 'http-proxy-middleware':

var proxyMiddleware = require('http-proxy-middleware');
server.middleware = proxyMiddleware('/api', {target: 'http://localhost:8888', changeOrigin: true});

For 'http-proxy-middleware' can get more info in: https://github.com/chimurai/http-proxy-middleware

2) Otherwise, we can add some logic on back end, e.g. if we use spring framework,  we can use @CrossOrigin annotation on method, class or global level. For global enabled we can add this annotation in one of the configuration classes is OK：

@Configuration @CrossOrigin public class WebConfig { }

3) Or we can just do something without code, say if we use Chrome, we can add the plugin

This will also avoid this error.

HTML 5 form validation not work with onclick

form validation is the form been validated before submit. So if you want to use HTML 5 default form validation with the submit button which has an onclick event, the form validation will not work as it is skipped, because these validations are performed when the form is submitted, in fact the button with onclick method just call a normal js function.

In order to make the default validation rule take effect, some issues should be considered:

1) for the submit button, we can use either:
<button type="submit">Submit</button>
or
<input type="submit" value="Submit">
the key point here is we should have the attribute inside: type="submit"

2) instead of using onclick, we should use onsubmit in the <form>, for instance:
<form onsubmit="aFunction()">...</form>
and then the aFunction() should be invoked when the form validation passed.

How to do the validation inside our own js function, HTML5 introduces a concept called "constraint validation" which is an algorithm browsers run when a form is submitted to determine its validity. To make this determination, the algorithm utilizes new HTML5 attributes like min, max, step, pattern, and required as well as existing attributes maxlength and type.

Another choise is validate the form using DOM API:

validity is a DOM property that will returns a validityState object which contains several boolean properties for us to use, say we have a node:
var ele = document.getElementById('someId');

Example	Validity property	Notes
<input id="someId" pattern="[0-9]{4}" value="123" />	ele.validity.patternMismatch	true if the node's value does not match its pattern attribute
<input id="someId" type="number" max="2" value="1" />	ele.validity.rangeOverflow	true if the node's value is greater than its max attribute
<input id="someId" type="number" min="2" value="3" />	ele.validity.rangeUnderflow	true if the node's value is less than its min attribute
<input id="someId" type="email" value="abc" />	ele.validity.typeMismatch	true if an input node's value is invalid per its type attribute
<input id="someId" type="text" required value=" " />	ele.validity.valueMissing	true if the node has a required attribute but has no value
<input id="someId" type="text" required value="" />	ele.validity.valid	true if all of the validity conditions listed above are false

checkValidity()

The checkValidity method on a form element node (e.g. input, select, textarea) returns true if the element contains valid data, for instance:

if(ele.checkValidity()){
...
}

On form nodes it returns true if all of the form's children contain valid data,i.e.
if(document.forms['aForm'].checkValidity()){
        ...
}

In fact we do not need <form> but only a <div></div> to accommodate all the input controls, and using a <button onclick="aFun(...params)"></button>, the validation rule can be performed as below:

    if(document.getElementById("firstName").validity.valueMissing){
        alert('firstName is required');
        return false;
    }else{
        user.firstName = document.getElementById("firstName").value;
    }

Eclipse Speed Up

Cleaning up history and indexes reduce the load on RAM, and overall HDD usage as well. This result in very high impact on performance. To remove the indexes and history folders, please cleanup all files/folders inside these two folders:

For cleaning up indexes

{workspace path}\.metadata\.plugins\org.eclipse.jdt.core

For cleaning up history

{workspace path}\.metadata\.plugins\org.eclipse.core.resources\.history

Here {workspace path} is the path of eclipse workspace where you create all projects.

Java Web Service SOAP REST

Simple introduction of JAX-WS and JAX-RS, with code, implementation, SOAP request and response, and comparison.

See Java Web Service