java.md

Java

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• JMS AMQP MQTT
  • JMS Java Messaging Service two message transfer type : queue or topic
    reply on java platform
  • AMQP Advanced Message Queueing Protocol multi-platform five transfer type : direct，fanout，topic，headers，system
  • MQTT Message Queueing Telemetry Transport low cpu occupied for small devices
• for java reference parameter ,u can design a new reference to the parameter
• load xxx.properties file? your can use

public class MybatisConfig {
    @Bean
    public PropertyPlaceholderConfigurer propertyPlaceholderConfigurer() {
        PropertyPlaceholderConfigurer propertyPlaceholderConfigurer = new PropertyPlaceholderConfigurer();
        propertyPlaceholderConfigurer.setLocation(new ClassPathResource("test.properties"));
        return propertyPlaceholderConfigurer;
    }
    public void test(@Value("${test.name}") String name){
    }
}

or simply use annotation

@PropertySource("classpath:test.properties")
public class MybatisConfig {
    public void test(@Value("${test.name}") String name){
    }

-too much @ComponentScan result in multiple execution of @Schedule schedule tasks in spring.

• Obeject parameter of method reset to a new handle wont change the value of the orignal one.For Integer and String, if you set its values(such as i=i+1),it wont change the orginal values too.(Maybe because every value-set equals to reset to a new handle)

Mybatis

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Note

• if the parameter is null then will pass (NULL) to database;
• return primary key

<insert id="addUser" useGeneratedKeys="true" keyProperty="resultId" keyColumn="id">
 ......
</insert>

• mybatis may return result that reuse obejects when using like association.Then u will ecounter circular referenced issues ($ref) using json tools.In FastJson u can use JSON.toJSONString(obj, SerializerFeature.DisableCircularReferenceDetect); or use global setting JSON.DEFAULT_GENERATE_FEATURE |= SerializerFeature.DisableCircularReferenceDetect.getMask();
• u cannot add any comment inside a sql statement!!!
• pass date as parameter add_time = #{record.addTime,jdbcType=TIMESTAMP}
• for %#{param}% using CONCAT('%','${param}','%' )

Spring

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Note

• if u want to use html which is as a static page, u may try this: add <mvc:annotation-driven/> <mvc:resources mapping="/static/**" location="/static/" /> to the springmvcServlet.xml and put all static resources like html pages into /webapp/static forder.Then just call return "/static/test.html?param=test" .
• for redirect ,do sth like this return "redirect:/static/test.html?param=test"
• @RestController is for return Object which will be automatically transformed into json.Also u can return page by return new ModelAndView("ur page name",'object name in jsp',object).
• when u want to pass a object to the server,u don't need to add any tag to the parameter.BUT mind that u should pass parameter like ?test=1&&name=2 rather than ?test.test=1&&test.name=2 and remove the @RequestParam
• version 5.1.33 of MySQL JDBC driver , u has to specify the serverTimezone explicitly in the connection string. jdbc:mysql://localhost/db?useUnicode=true&useJDBCCompliantTimezoneShift=true&useLegacyDatetimeCode=false&serverTimezone=UTC
• if u want to pass an object to the controller, u can simply remove the @RequestParam annotation. Pass an json or use A=?&B=? is OK
• how to set ur method return as JSON? use @RestController and @RequestMapping("test") or @RequestMapping(value = "/test", produces = "application/json") @ResponseBody
• let controller return object not including null properties: add @JsonInclude(Include.NON_NULL) annotation to the specific modal
• requestMaping("test") may conflict with addResourceHandler("/*.text") when accessing www.test.com/testproject/test,both text file and controller with respond and got 406 error: The resource identified by this request is only capable of generating responses with characteristics not acceptable according to the request "accept" headers.