在Spring Boot中使用拦截器，可在以下情况下执行操作 -
- 在将请求发送到控制器之前
- 在将响应发送给客户端之前
例如，使用拦截器在将请求发送到控制器之前添加请求标头，并在将响应发送到客户端之前添加响应标头。
要使用拦截器，需要创建支持它的@Component类，它应该实现HandlerInterceptor接口。
以下是在拦截器上工作时应该了解的三种方法 -
preHandle()方法 - 用于在将请求发送到控制器之前执行操作。此方法应返回true，以将响应返回给客户端。postHandle()方法 - 用于在将响应发送到客户端之前执行操作。afterCompletion()方法 - 用于在完成请求和响应后执行操作。
请注意以下代码以便更好地理解 -
@Component
public class ProductServiceInterceptor implements HandlerInterceptor {
@Override
public boolean preHandle(
HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {
return true;
}
@Override
public void postHandle(
HttpServletRequest request, HttpServletResponse response, Object handler,
ModelAndView modelAndView) throws Exception {}
@Override
public void afterCompletion(HttpServletRequest request, HttpServletResponse response,
Object handler, Exception exception) throws Exception {}
}
必须使用WebMvcConfigurerAdapter向InterceptorRegistry注册此Interceptor，如下所示 -
@Component
public class ProductServiceInterceptorAppConfig extends WebMvcConfigurerAdapter {
@Autowired
ProductServiceInterceptor productServiceInterceptor;
@Override
public void addInterceptors(InterceptorRegistry registry) {
registry.addInterceptor(productServiceInterceptor);
}
}
在下面给出的示例中，将使用GET产品API，该API提供的输出如下 -Interceptor类ProductServiceInterceptor.java的代码如下 -
package com.yiibai.demo.interceptor;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import org.springframework.stereotype.Component;
import org.springframework.web.servlet.HandlerInterceptor;
import org.springframework.web.servlet.ModelAndView;
@Component
public class ProductServiceInterceptor implements HandlerInterceptor {
@Override
public boolean preHandle
(HttpServletRequest request, HttpServletResponse response, Object handler)
throws Exception {
System.out.println("Pre Handle method is Calling");
return true;
}
@Override
public void postHandle(HttpServletRequest request, HttpServletResponse response,
Object handler, ModelAndView modelAndView) throws Exception {
System.out.println("Post Handle method is Calling");
}
@Override
public void afterCompletion
(HttpServletRequest request, HttpServletResponse response, Object
handler, Exception exception) throws Exception {
System.out.println("Request and Response is completed");
}
}
应用程序配置类文件的代码将拦截器注册到拦截器注册表,ProductServiceInterceptorAppConfig.java如下 -
package com.yiibai.demo.interceptor;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Component;
import org.springframework.web.servlet.config.annotation.InterceptorRegistry;
import org.springframework.web.servlet.config.annotation.WebMvcConfigurerAdapter;
@Component
public class ProductServiceInterceptorAppConfig extends WebMvcConfigurerAdapter {
@Autowired
ProductServiceInterceptor productServiceInterceptor;
@Override
public void addInterceptors(InterceptorRegistry registry) {
registry.addInterceptor(productServiceInterceptor);
}
}
控制器类文件ProductServiceController.java的代码如下 -
package com.yiibai.demo.controller;
import java.util.HashMap;
import java.util.Map;
import org.springframework.http.HttpStatus;
import org.springframework.http.ResponseEntity;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.RequestBody;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;
import org.springframework.web.bind.annotation.RestController;
import com.yiibai.demo.exception.ProductNotfoundException;
import com.yiibai.demo.model.Product;
@RestController
public class ProductServiceController {
private static Map<String, Product> productRepo = new HashMap<>();
static {
Product honey = new Product();
honey.setId("1");
honey.setName("Honey");
productRepo.put(honey.getId(), honey);
Product almond = new Product();
almond.setId("2");
almond.setName("Almond");
productRepo.put(almond.getId(), almond);
}
@RequestMapping(value = "/products")
public ResponseEntity<Object> getProduct() {
return new ResponseEntity<>(productRepo.values(), HttpStatus.OK);
}
}
POJO类Product.java 代码如下 -
package com.yiibai.demo.model;
public class Product {
private String id;
private String name;
public String getId() {
return id;
}
public void setId(String id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
}
Spring Boot应用程序类主要的文件DemoApplication.java 的代码如下 -
package com.yiibai.demo;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
@SpringBootApplication
public class DemoApplication {
public static void main(String[] args) {
SpringApplication.run(DemoApplication.class, args);
}
}
Maven build的代码 - pom.xml 如下所示 -
<?xml version = "1.0" encoding = "UTF-8"?>
<project xmlns = "http://maven.apache.org/POM/4.0.0" xmlns:xsi = "
http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation = "http://maven.apache.org/POM/4.0.0
http://maven.apache.org/xsd/maven-4.0.0.xsd">
<modelVersion>4.0.0</modelVersion>
<groupId>com.yiibai</groupId>
<artifactId>demo</artifactId>
<version>0.0.1-SNAPSHOT</version>
<packaging>jar</packaging>
<name>demo</name>
<description>Demo project for Spring Boot</description>
<parent>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-parent</artifactId>
<version>1.5.8.RELEASE</version>
<relativePath/>
</parent>
<properties>
<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
<project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
<java.version>1.8</java.version>
</properties>
<dependencies>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-web</artifactId>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-test</artifactId>
<scope>test</scope>
</dependency>
</dependencies>
<build>
<plugins>
<plugin>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-maven-plugin</artifactId>
</plugin>
</plugins>
</build>
</project>
这里显示了Gradle构建文件：build.gradle 的代码 -
buildscript {
ext {
springBootVersion = '1.5.8.RELEASE'
}
repositories {
mavenCentral()
}
dependencies {
classpath("org.springframework.boot:spring-boot-gradle-plugin:${springBootVersion}")
}
}
apply plugin: 'java'
apply plugin: 'eclipse'
apply plugin: 'org.springframework.boot'
group = 'com.yiibai'
version = '0.0.1-SNAPSHOT'
sourceCompatibility = 1.8
repositories {
mavenCentral()
}
dependencies {
compile('org.springframework.boot:spring-boot-starter-web')
testCompile('org.springframework.boot:spring-boot-starter-test')
}
创建可执行的JAR文件，并使用以下Maven或Gradle命令运行Spring Boot应用程序。
对于Maven，使用如下所示的命令 -
mvn clean install
在控制台上看到"BUILD SUCCESS"输出之后，在target目录下找到JAR文件。对于Gradle，使用如下所示的命令 -
gradle clean build
在控制台上看到"BUILD SUCCESSFUL"之后，在build/libs目录下找到JAR文件。使用以下命令运行JAR文件 -
java –jar <JARFILE>
现在，应用程序已在Tomcat端口8080上启动，如下所示 -
打开 POSTMAN 应用程序中的URL，并输入：http://localhost:8080/products，看到输出如下 -
在控制台窗口中，看到在拦截器中添加的System.out.println语句，如下面给出的屏幕截图所示 -
