Spring注解记录

记录工作中见到的注解，共同学习，一起进步，如有错误，欢迎指正，欢迎补充！

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1. @Conditional

@Conditional是Spring4新提供的注解，它的作用是按照一定的条件进行判断，满足条件给容器注册bean。
@Conditional的定义：

@Target({ElementType.TYPE, ElementType.METHOD})
@Retention(RetentionPolicy.RUNTIME) 
@Documented
public @interface Conditional {
    Class<? extends Condition>[] value();
}

从代码中可以看到，需要传入一个Class数组，并且需要继承Condition接口：

public interface Condition {
    boolean matches(ConditionContext var1, AnnotatedTypeMetadata var2);
}

Condition是个接口，需要实现matches方法，返回true则注入bean，false则不注入。
具体用法请参考示例：文章链接

派生

@ConditionalOnMissingBean(HttpUtils.class)
当缺少某个Bean时注入。

2.@Scope("prototype")

• singleton 表示在spring容器中的单例，通过spring容器获得该bean时总是返回唯一的实例
• prototype表示每次获得bean都会生成一个新的对象
• request表示在一次http请求内有效（只适用于web应用）
• session表示在一个用户会话内有效（只适用于web应用）
• globalSession表示在全局会话内有效（只适用于web应用）

3.@Configurable

用来自动注入bean的注解，不需要通过BeanFactory去获取

示例

定义了一个httpclient的工具类：

import org.apache.http.HttpEntity;
import org.apache.http.NameValuePair;
import org.apache.http.client.entity.UrlEncodedFormEntity;
import org.apache.http.client.methods.CloseableHttpResponse;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.client.methods.HttpPost;
import org.apache.http.client.methods.HttpUriRequest;
import org.apache.http.entity.ContentType;
import org.apache.http.entity.StringEntity;
import org.apache.http.impl.client.CloseableHttpClient;
import org.apache.http.message.BasicNameValuePair;
import org.apache.http.util.EntityUtils;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Component;
import org.springframework.util.Assert;
import org.springframework.util.StreamUtils;

import java.io.*;
import java.util.ArrayList;
import java.util.List;
import java.util.Map;

@Component
public class HttpUtils {

    @Autowired
    private CloseableHttpClient httpClient;

    public String doGet(String url) {
        String respStr = this.doGet(url, null);
        return respStr;
    }

    public String doGet(String url, Map<String, String> headerMap) {
        HttpGet get = new HttpGet(url);
        if (headerMap != null && headerMap.size() > 0) {
            headerMap.forEach((k, v) -> {
                get.setHeader(k, v);
            });
        }
        String respStr = this.doHttp(get);
        return respStr;
    }

    public String doPostForm(String url, Map<String, String> data) {
        String respStr = this.doPostForm(url, null, data);
        return respStr;
    }

    public String doPostForm(String url, Map<String, String> header, Map<String, String> data) {
        HttpPost post = new HttpPost(url);
        if (header != null) {
            header.forEach((name, value) -> post.addHeader(name, value));
        }
        List<NameValuePair> pairList = new ArrayList<>(data.size());
        for (Map.Entry<String, String> entry : data.entrySet()) {
            NameValuePair pair = new BasicNameValuePair(entry.getKey(), entry.getValue());
            pairList.add(pair);
        }

        UrlEncodedFormEntity entity = null;
        try {
            entity = new UrlEncodedFormEntity(pairList, "UTF-8");
        } catch (UnsupportedEncodingException e) {
        }
        post.setEntity(entity);

        String respStr = this.doHttp(post);
        return respStr;
    }

    public <T> String doPostJson(String url, T data) {
        String respStr = this.doPostJson(url, null, data);
        return respStr;
    }

    public <T> String doPostJson(String url, Map<String, String> header, T data) {
        ContentType contentType = ContentType.APPLICATION_JSON;
        String respStr = this.doPostJson(url, contentType, header, data);
        return respStr;
    }

    public <T> String doPostJson(String url, ContentType contentType, Map<String, String> header, T data) {
        HttpPost post = new HttpPost(url);
        if (header != null) {
            header.forEach((name, value) -> post.addHeader(name, value));
        }

        if (contentType == null) {
            contentType = ContentType.APPLICATION_JSON;
        }

        String jsonString = JsonUtils.beanToJson(data);

        StringEntity entity = new StringEntity(jsonString, contentType);
        post.setEntity(entity);

        String respStr = this.doHttp(post);
        return respStr;
    }

    /**
     * 下载文件。
     *
     * @param url      下载地址
     * @param savePath 保存的物理路径
     * @param fileName 保存的文件名。
     * @return 下载成功，还是失败。
     */
    public boolean download(String url, String savePath, String fileName) {
        String saveFileName = this.doDownload(url, savePath, fileName);
        File file = new File(saveFileName);
        if (!file.exists()) {
            return false;
        }
        return FileUtils.sizeOf(file) > 0;
    }


    private String doHttp(HttpUriRequest request) {
        String respStr = null;
        // 发起请求
        CloseableHttpResponse response = null;
        try {
            response = this.httpClient.execute(request);
            HttpEntity responseEntity = response.getEntity();
            respStr = EntityUtils.toString(responseEntity);
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            if (response != null) {
                try {
                    response.close();
                } catch (IOException e) {
                }
            }
        }
        return respStr;
    }

    private String doDownload(String url, String savePath, String fileName) {
        Assert.isNull(savePath, "HTTP下载的存储路径不能为空！");
        String saveFileName = null;
        String respStr = null;
        // 发起请求
        CloseableHttpResponse response = null;
        try {
            //文件保存位置
            File saveDir = new File(savePath);
            if (!saveDir.exists()) {
                saveDir.mkdirs();
            }

            saveFileName = saveDir + File.separator + fileName;
            File file = new File(saveFileName);
            if (!file.getParentFile().exists()) {
                file.mkdirs();
            }
            FileOutputStream fos = new FileOutputStream(file);
            HttpGet request = new HttpGet(url);
            response = this.httpClient.execute(request);
            HttpEntity responseEntity = response.getEntity();
            InputStream content = responseEntity.getContent();
            StreamUtils.copy(content, fos);
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            if (response != null) {
                try {
                    response.close();
                } catch (IOException e) {
                }
            }
        }
        return saveFileName;
    }
}

配置类：

import org.springframework.beans.factory.annotation.Configurable;
import org.springframework.boot.autoconfigure.condition.ConditionalOnMissingBean;
import org.springframework.context.annotation.Bean;

@Configurable
public class AppConfig {
    @ConditionalOnMissingBean(HttpUtils.class)
    @Bean
    public HttpUtils getHttpUtils() {
        return new HttpUtils();
    }
}

使用：

public abstract class BaseServiceImpl<T> implements BaseService<T> {

    private HttpUtils httpUtils; 
  
    public BaseServiceImpl(HttpUtils httpUtils) {
        this.httpUtils = httpUtils;
    }
}

public class aServiceImpl extends BaseServiceImpl<Result> {

    @Autowired
    public aServiceImpl (HttpUtils httpUtils) {
        super(httpUtils);
    }
}

当找不到HttpUtils时，会自动注入。