Master Advanced Spring Boot 3 Techniques: Output Control, Body Parsing, and Security Context

Spring Boot 3.2.5 provides many flexible ways to handle request and response data. Below are several practical techniques.

1. Directly control output content

You can define OutputStream or Writer parameters in a controller method and write directly to the response.

<code>@GetMapping("/index")
public void index(OutputStream os, HttpServletResponse response) throws Exception {
    response.setContentType("text/plain;charset=utf-8");
    os.write("中国🇨🇳".getBytes());
}</code>

2. Manually read request body

When you need to parse the request body yourself, use InputStream or Reader parameters.

<code>@PostMapping("/index")
public void index(InputStream is, HttpServletResponse response) throws Exception {
    response.setContentType("application/json;charset=utf-8");
    StringBuilder sb = new StringBuilder();
    String line = null;
    InputStreamReader isr = new InputStreamReader(is, StandardCharsets.UTF_8);
    BufferedReader br = new BufferedReader(isr);
    while ((line = br.readLine()) != null) {
        sb.append(line);
    }
    response.getWriter().println(sb.toString());
}</code>

3. Fixed values with @Value

Use @Value to inject configuration values directly into method parameters.

<code>@GetMapping("/index")
public Object index(@Value("${pack.controller.params.version:}") String version) {
    return version;
}</code>

Configuration file:

<code>pack:
  controller:
    params:
      version: 1.0.1</code>

4. Using SpEL expressions

<code>@GetMapping("/spel")
public Object spel(@Value("#{systemProperties['java.home']}") String javaHome) {
    return javaHome;
}</code>

5. Retrieve body and headers together

Define a parameter of type HttpEntity to access both request body and headers.

<code>@PostMapping("/index")
public Object index(HttpEntity<User> entity) {
    System.out.printf("headers: %s%n", entity.getHeaders());
    return entity.getBody();
}
public static record User(Long id, String name) {}
</code>

6. Access security context data

When Spring Security is enabled, you can inject data from the current security context directly.

<code>@GetMapping("/name")
public Object name(@CurrentSecurityContext(expression = "authentication.name") String name) {
    return name;
}</code>

Other examples:

<code>@CurrentSecurityContext(expression = "authentication.authorities")
@CurrentSecurityContext SecurityContext context
</code>

7. Special Map parameters

You can bind a Map parameter to model attributes using @ModelAttribute .

<code>@ModelAttribute("user")
public User init(User user) {
    return user;
}
@GetMapping("/index")
public Object index(Map<String, Object> map) {
    // Retrieve the user object populated by @ModelAttribute
    return map.get("user");
}
</code>

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