read-config-properties

Author: Snailclimb

docs/basis/Untitled.md

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+很多时候我们需要将一些常用的配置信息比如阿里云oss配置、发送短信的相关信息配置等等放到配置文件中。
+
+下面我们来看一下 Spring 为我们提供了哪些方式帮助我们从配置文件中读取这些配置信息。
+
+`application.yml` 内容如下：
+
+```yaml
+wuhan2020: 2020年初武汉爆发了新型冠状病毒，疫情严重，但是，我相信一切都会过去！武汉加油！中国加油！
+
+my-profile:
+  name: Guide哥
+  email: koushuangbwcx@163.com
+
+library:
+  location: 湖北武汉加油中国加油
+  books:
+    - name: 天才基本法
+      description: 二十二岁的林朝夕在父亲确诊阿尔茨海默病这天，得知自己暗恋多年的校园男神裴之即将出国深造的消息——对方考取的学校，恰是父亲当年为她放弃的那所。
+    - name: 时间的秩序
+      description: 为什么我们记得过去，而非未来？时间“流逝”意味着什么？是我们存在于时间之内，还是时间存在于我们之中？卡洛·罗韦利用诗意的文字，邀请我们思考这一亘古难题——时间的本质。
+    - name: 了不起的我
+      description: 如何养成一个新习惯？如何让心智变得更成熟？如何拥有高质量的关系？ 如何走出人生的艰难时刻？
+
+```
+
+### 1.通过 `@value` 读取比较简单的配置信息
+
+使用  `@Value("${property}")` 读取比较简单的配置信息：
+
+```java
+@Value("${wuhan2020}")
+String wuhan2020;
+```
+
+> **需要注意的是 `@value`这种方式是不被推荐的，Spring 比较建议的是下面几种读取配置信息的方式。**
+
+### 2.通过`@ConfigurationProperties`读取并与 bean 绑定
+
+>  **`LibraryProperties` 类上加了 `@Component` 注解，我们可以像使用普通 bean 一样将其注入到类中使用。**
+
+```java
+
+import lombok.Getter;
+import lombok.Setter;
+import lombok.ToString;
+import org.springframework.boot.context.properties.ConfigurationProperties;
+import org.springframework.context.annotation.Configuration;
+import org.springframework.stereotype.Component;
+
+import java.util.List;
+
+@Component
+@ConfigurationProperties(prefix = "library")
+@Setter
+@Getter
+@ToString
+class LibraryProperties {
+    private String location;
+    private List<Book> books;
+
+    @Setter
+    @Getter
+    @ToString
+    static class Book {
+        String name;
+        String description;
+    }
+}
+
+```
+
+这个时候你就可以像使用普通 bean 一样，将其注入到类中使用：
+
+```java
+package cn.javaguide.readconfigproperties;
+
+import org.springframework.beans.factory.InitializingBean;
+import org.springframework.boot.SpringApplication;
+import org.springframework.boot.autoconfigure.SpringBootApplication;
+
+/**
+ * @author shuang.kou
+ */
+@SpringBootApplication
+public class ReadConfigPropertiesApplication implements InitializingBean {
+
+    private final LibraryProperties library;
+
+    public ReadConfigPropertiesApplication(LibraryProperties library) {
+        this.library = library;
+    }
+
+    public static void main(String[] args) {
+        SpringApplication.run(ReadConfigPropertiesApplication.class, args);
+    }
+
+    @Override
+    public void afterPropertiesSet() {
+        System.out.println(library.getLocation());
+        System.out.println(library.getBooks());    }
+}
+```
+
+控制台输出：
+
+```
+湖北武汉加油中国加油
+[LibraryProperties.Book(name=天才基本法, description........]
+```
+
+### 3.通过`@ConfigurationProperties`读取并校验
+
+我们先将`application.yml`修改为如下内容，明显看出这不是一个正确的 email 格式：
+
+```yaml
+my-profile:
+  name: Guide哥
+  email: koushuangbwcx@
+```
+
+>**`ProfileProperties` 类没有加 `@Component` 注解。我们在我们要使用`ProfileProperties` 的地方使用`@EnableConfigurationProperties`注册我们的配置bean：**
+
+ ```java
+import lombok.Getter;
+import lombok.Setter;
+import lombok.ToString;
+import org.springframework.boot.context.properties.ConfigurationProperties;
+import org.springframework.stereotype.Component;
+import org.springframework.validation.annotation.Validated;
+
+import javax.validation.constraints.Email;
+import javax.validation.constraints.NotEmpty;
+
+/**
+ * @author shuang.kou
+ */
+@Getter
+@Setter
+@ToString
+@ConfigurationProperties("my-profile")
+@Validated
+public class ProfileProperties {
+    @NotEmpty
+    private String name;
+
+    @Email
+    @NotEmpty
+    private String email;
+  
+    //配置文件中没有读取到的话就用默认值
+    private Boolean handsome = Boolean.TRUE;
+
+}
+ ```
+
+具体使用：
+
+```java
+package cn.javaguide.readconfigproperties;
+
+import org.springframework.beans.factory.InitializingBean;
+import org.springframework.beans.factory.annotation.Value;
+import org.springframework.boot.SpringApplication;
+import org.springframework.boot.autoconfigure.SpringBootApplication;
+import org.springframework.boot.context.properties.EnableConfigurationProperties;
+
+/**
+ * @author shuang.kou
+ */
+@SpringBootApplication
+@EnableConfigurationProperties(ProfileProperties.class)
+public class ReadConfigPropertiesApplication implements InitializingBean {
+    private final ProfileProperties profileProperties;
+
+    public ReadConfigPropertiesApplication(ProfileProperties profileProperties) {
+        this.profileProperties = profileProperties;
+    }
+
+    public static void main(String[] args) {
+        SpringApplication.run(ReadConfigPropertiesApplication.class, args);
+    }
+
+    @Override
+    public void afterPropertiesSet() {
+        System.out.println(profileProperties.toString());
+    }
+}
+
+```
+
+因为我们的邮箱格式不正确，所以程序运行的时候就报错，根本运行不起来，保证了数据类型的安全性：
+
+```visual basic
+Binding to target org.springframework.boot.context.properties.bind.BindException: Failed to bind properties under 'my-profile' to cn.javaguide.readconfigproperties.ProfileProperties failed:
+
+    Property: my-profile.email
+    Value: koushuangbwcx@
+    Origin: class path resource [application.yml]:5:10
+    Reason: must be a well-formed email address
+```
+
+我们把邮箱测试改为正确的之后再运行，控制台就能成功打印出读取到的信息：
+
+```
+ProfileProperties(name=Guide哥, email=koushuangbwcx@163.com, handsome=true)
+```
+
+### 4.`@PropertySource`读取指定 properties 文件
+
+```java
+import lombok.Getter;
+import lombok.Setter;
+import org.springframework.beans.factory.annotation.Value;
+import org.springframework.context.annotation.PropertySource;
+import org.springframework.stereotype.Component;
+
+@Component
+@PropertySource("classpath:website.properties")
+@Getter
+@Setter
+class WebSite {
+    @Value("${url}")
+    private String url;
+}
+```
+
+使用：
+
+```java
+@Autowired
+private WebSite webSite;
+
+System.out.println(webSite.getUrl());//https://javaguide.cn/
+
+```
+
+### 5.题外话:Spring加载配置文件的优先级
+
+Spring 读取配置文件也是有优先级的，直接上图：
+
+<img src="https://my-blog-to-use.oss-cn-beijing.aliyuncs.com/2019-11/read-config-properties-priority.jpg" style="zoom:50%;" />
+
+更对内容请查看官方文档：https://docs.spring.io/spring-boot/docs/current/reference/html/spring-boot-features.html#boot-features-external-config
+
+> 本文源码：

docs/basis/read-config-properties.md

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+HELP.md
+target/
+!.mvn/wrapper/maven-wrapper.jar
+!**/src/main/**
+!**/src/test/**
+
+### STS ###
+.apt_generated
+.classpath
+.factorypath
+.project
+.settings
+.springBeans
+.sts4-cache
+
+### IntelliJ IDEA ###
+.idea
+*.iws
+*.iml
+*.ipr
+
+### NetBeans ###
+/nbproject/private/
+/nbbuild/
+/dist/
+/nbdist/
+/.nb-gradle/
+build/
+
+### VS Code ###
+.vscode/

source-code/basis/read-config-properties/.gitignore

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+/*
+ * Copyright 2007-present the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+import java.net.*;
+import java.io.*;
+import java.nio.channels.*;
+import java.util.Properties;
+
+public class MavenWrapperDownloader {
+
+    private static final String WRAPPER_VERSION = "0.5.6";
+    /**
+     * Default URL to download the maven-wrapper.jar from, if no 'downloadUrl' is provided.
+     */
+    private static final String DEFAULT_DOWNLOAD_URL = "https://repo.maven.apache.org/maven2/io/takari/maven-wrapper/"
+            + WRAPPER_VERSION + "/maven-wrapper-" + WRAPPER_VERSION + ".jar";
+
+    /**
+     * Path to the maven-wrapper.properties file, which might contain a downloadUrl property to
+     * use instead of the default one.
+     */
+    private static final String MAVEN_WRAPPER_PROPERTIES_PATH =
+            ".mvn/wrapper/maven-wrapper.properties";
+
+    /**
+     * Path where the maven-wrapper.jar will be saved to.
+     */
+    private static final String MAVEN_WRAPPER_JAR_PATH =
+            ".mvn/wrapper/maven-wrapper.jar";
+
+    /**
+     * Name of the property which should be used to override the default download url for the wrapper.
+     */
+    private static final String PROPERTY_NAME_WRAPPER_URL = "wrapperUrl";
+
+    public static void main(String args[]) {
+        System.out.println("- Downloader started");
+        File baseDirectory = new File(args[0]);
+        System.out.println("- Using base directory: " + baseDirectory.getAbsolutePath());
+
+        // If the maven-wrapper.properties exists, read it and check if it contains a custom
+        // wrapperUrl parameter.
+        File mavenWrapperPropertyFile = new File(baseDirectory, MAVEN_WRAPPER_PROPERTIES_PATH);
+        String url = DEFAULT_DOWNLOAD_URL;
+        if (mavenWrapperPropertyFile.exists()) {
+            FileInputStream mavenWrapperPropertyFileInputStream = null;
+            try {
+                mavenWrapperPropertyFileInputStream = new FileInputStream(mavenWrapperPropertyFile);
+                Properties mavenWrapperProperties = new Properties();
+                mavenWrapperProperties.load(mavenWrapperPropertyFileInputStream);
+                url = mavenWrapperProperties.getProperty(PROPERTY_NAME_WRAPPER_URL, url);
+            } catch (IOException e) {
+                System.out.println("- ERROR loading '" + MAVEN_WRAPPER_PROPERTIES_PATH + "'");
+            } finally {
+                try {
+                    if (mavenWrapperPropertyFileInputStream != null) {
+                        mavenWrapperPropertyFileInputStream.close();
+                    }
+                } catch (IOException e) {
+                    // Ignore ...
+                }
+            }
+        }
+        System.out.println("- Downloading from: " + url);
+
+        File outputFile = new File(baseDirectory.getAbsolutePath(), MAVEN_WRAPPER_JAR_PATH);
+        if (!outputFile.getParentFile().exists()) {
+            if (!outputFile.getParentFile().mkdirs()) {
+                System.out.println(
+                        "- ERROR creating output directory '" + outputFile.getParentFile().getAbsolutePath() + "'");
+            }
+        }
+        System.out.println("- Downloading to: " + outputFile.getAbsolutePath());
+        try {
+            downloadFileFromURL(url, outputFile);
+            System.out.println("Done");
+            System.exit(0);
+        } catch (Throwable e) {
+            System.out.println("- Error downloading");
+            e.printStackTrace();
+            System.exit(1);
+        }
+    }
+
+    private static void downloadFileFromURL(String urlString, File destination) throws Exception {
+        if (System.getenv("MVNW_USERNAME") != null && System.getenv("MVNW_PASSWORD") != null) {
+            String username = System.getenv("MVNW_USERNAME");
+            char[] password = System.getenv("MVNW_PASSWORD").toCharArray();
+            Authenticator.setDefault(new Authenticator() {
+                @Override
+                protected PasswordAuthentication getPasswordAuthentication() {
+                    return new PasswordAuthentication(username, password);
+                }
+            });
+        }
+        URL website = new URL(urlString);
+        ReadableByteChannel rbc;
+        rbc = Channels.newChannel(website.openStream());
+        FileOutputStream fos = new FileOutputStream(destination);
+        fos.getChannel().transferFrom(rbc, 0, Long.MAX_VALUE);
+        fos.close();
+        rbc.close();
+    }
+
+}