ppdouble/hellopemo

How to use springboot, how to use servlet in springboot, how to use static file and freemarker

Servlet

Two ways to use servlet:

Method 1

In the entry class of Application using @ServletComponentScan.

In the controller the code could be writing as below:

@WebServlet(name = "HelloServlet", value = "/helloservlet")
public class HelloServlet extends HttpServlet {}

@WebFilter(filterName = "helloFilter", urlPatterns = "/hellofilter")
public class HelloFilter implements Filter {}

@WebListener
public class HelloListener implements ServletContextListener {}

Method 2

treated all stuff as bean and registered controller in the entry class of application

@Bean
public ServletRegistrationBean getServletRegistrationBean() {
    ServletRegistrationBean servletRegistrationBean = new ServletRegistrationBean(new HelloServlet());
    servletRegistrationBean.addUrlMappings("/helloservlet");
    return servletRegistrationBean;
}

@Bean
public FilterRegistrationBean getFilterRegistrationBean() {
    FilterRegistrationBean filterRegistrationBean = new FilterRegistrationBean(new HelloFilter());
    filterRegistrationBean.addUrlPatterns("/hellofilter");
    return filterRegistrationBean;
}

@Bean
public ServletListenerRegistrationBean<HelloListener> getServletListenerRegistrationBean() {
    ServletListenerRegistrationBean servletListenerRegistrationBean = new ServletListenerRegistrationBean(new HelloListener());
    return servletListenerRegistrationBean;
}

Return json string

Two ways:

Method 1 @RestController to the controller class

@RestController
public class HelloController {
    
    private Map<String, Object> result = new HashMap<>();
    ...
    @RequestMapping("/hello")
    public Map<String, Object> hello() {
        ...
        return result;
    }
}

Method 2 @Controller to the controller class and @ResponseBody to the method

@Controller
public class HelloController {

    private Map<String, Object> result = new HashMap<>();
    ...
    @RequestMapping("/hello")
    @ResponseBody
    public Map<String, Object> hello() {
        ...
        return result;
    }
}

Render to freemarker

Three tips:

1. Do not use @ResponseBody or @RestController
2. The controller should return the file name (without suffix) of the template file
3. The variable name which add to Model should be same with the variable in the template file

controler

@Controller
public class StudentList {
 
    @RequestMapping("/liststudents")
    public String studentlist(Model model) {
        List<Student> studentList = new ArrayList<>();
        ...
        model.addAttribute("slist", studentList); // the attrbuteName should same with the corresponding variable the template file
        return "studentlist"; // same with the template file name
    }
}

template

studentlist.ftlh

    <#list slist as student>
    <tr>
        <td>${student.id}</td>
        <td>${student.studentName}</td>
        <td>${student.grade}</td>
    <tr>
    </#list>

other

application.properties

# Default value true
#spring.freemarker.enabled=true
# Default value /templates
#spring.freemarker.template-loader-path=classpath:/templates
# Default value ftlh
#spring.freemarker.suffix=.ftlh

pom.xml

		<dependency>
			<groupId>org.springframework.boot</groupId>
			<artifactId>spring-boot-starter-freemarker</artifactId>
		</dependency>