java获取网络图片读InputStream

桃扇骨 2024-02-22 03:00 50阅读 0赞

**目录**

省流：

不推荐使用的方法：

推荐写法：

原始写法：

现代写法：

对比：

--------------------

### 省流： ###

通常使用（经过验证，生产放心食用）：

try (CloseableHttpClient httpClient = HttpClientBuilder.create().build()) {
                HttpGet httpGet = new HttpGet(path);
                CloseableHttpResponse resp = httpClient.execute(httpGet);// 调用服务器接口
                byte[] data = EntityUtils.toByteArray(resp.getEntity());// 将返回的图片或者文件转化成字节数组的形式
                BASE64Encoder encoder = new BASE64Encoder();
                String imageBase64 = encoder.encode(data);
    //            String imageBase64 = "data:image/jpg;base64," + encoder.encodeBuffer(data).trim();
    //            imageBase64 = imageBase64.replaceAll("\n", "").replaceAll("\r", "").replaceAll(" ", "");//删除 \r\n
                return imageBase64;
            } catch (Exception e) {
                log.error("获取图片异常:{}",e.getMessage());
            }

其中的核心代码：

//拿到了装有数据的byte数组，即将数据从http的流(inputstream)中取了出来
    byte[] data = EntityUtils.toByteArray(resp.getEntity());

### 不推荐使用的方法： ###

//v1.0
      int count = in.available();
      byte[] b = new byte[count];
    
    //v2.0
      int count = 0;
      while (count == 0) {
       count = in.available();
      }
      byte[] b = new byte[count];
      in.read(b);
    
    //v3.0
      int count = 0;
      while (count == 0) {
       count = in.available();
      }
      byte[] b = new byte[count];
      int readCount = 0; // 已经成功读取的字节的个数
      while (readCount < count) {
       readCount += in.read(bytes, readCount, count - readCount);
      }

对于上述写法，网上的一种说法：网络操作时往往出错，因为你调用available()方法时，对方发送的数据可能还没有到达，你得到的count是0。

### 推荐写法： ###

#### 原始写法： ####

读网络流，不是用上面这种方式。而是要给定一个定长的byte数组，去循环读取流。

InputStream in = entity.getContent();//entity是请求数据时获取来的HttpEntity实例
    ByteArrayOutputStream out = new ByteArrayOutputStream();
    byte[] cache = new byte[1024];
    int nRead = 0;
    while ((nRead = in.read(cache)) != -1) {
           out.write(cache, 0, nRead);
           out.flush();
    }
    out.close();
    in.close();
    byte[] mBytes = out.toByteArray();

#### 现代写法： ####

但上面这种方法一般都不用了，直接用下面现成的库：

try (CloseableHttpClient httpClient = HttpClientBuilder.create().build()) {
                HttpGet httpGet = new HttpGet(path);
                CloseableHttpResponse  resp = httpClient.execute(httpGet);// 调用服务器接口
                byte[] data = EntityUtils.toByteArray(resp.getEntity());// 将返回的图片或者文件转化成字节数组的形式
                BASE64Encoder encoder = new BASE64Encoder();
                String imageBase64 = encoder.encode(data);
    //            String imageBase64 = "data:image/jpg;base64," + encoder.encodeBuffer(data).trim();
    //            imageBase64 = imageBase64.replaceAll("\n", "").replaceAll("\r", "").replaceAll(" ", "");//删除 \r\n
                return imageBase64;
            } catch (Exception e) {
                log.error("获取图片异常:{}",e.getMessage());
            }

会发现，直接通过这行代码就得到了装有数据的byte数组。

byte[] data = EntityUtils.toByteArray(resp.getEntity());

#### 对比： ####

如果不使用现成的库，想自己实现，就得使用原始写法，这样写：

CloseableHttpClient httpClient = HttpClientBuilder.create().build();
                HttpGet httpGet = new HttpGet(path);
                CloseableHttpResponse resp = httpClient.execute(httpGet);// 调用服务器接口
                HttpEntity entity = resp.getEntity();
                InputStream in = entity.getContent();
                ByteArrayOutputStream out = new ByteArrayOutputStream();
                byte[] cache = new byte[1024];
                int nRead = 0;
                while ((nRead = in.read(cache)) != -1) {
                    out.write(cache, 0, nRead);
                    out.flush();
                }

上古文章，可以作为参考：

[java InputStream读取数据问题 - java小强 - ITeye博客][java InputStream_ - java_ - ITeye]

[inputstream.available()方法适用情况\_拖鞋村长\_新浪博客][inputstream.available]

=========================分割线=========================

文章到此已经结束，以下是紫薯布丁

try (CloseableHttpClient httpClient = HttpClientBuilder.create().build()) \{  
HttpGet httpGet = new HttpGet(path);  
CloseableHttpResponse resp = httpClient.execute(httpGet);// 调用服务器接口  
byte\[\] data = EntityUtils.toByteArray(resp.getEntity());// 将返回的图片或者文件转化成字节数组的形式  
BASE64Encoder encoder = new BASE64Encoder();  
String imageBase64 = encoder.encode(data);  
// String imageBase64 = "data:image/jpg;base64," + encoder.encodeBuffer(data).trim();  
// imageBase64 = imageBase64.replaceAll("\\n", "").replaceAll("\\r", "").replaceAll(" ", "");//删除 \\r\\n  
return imageBase64;  
\} catch (Exception e) \{  
log.error("获取图片异常:\{\}",e.getMessage());  
\}

//v1.0  
int count = in.available();  
byte\[\] b = new byte\[count\];

//v2.0  
int count = 0;  
while (count == 0) \{  
count = in.available();  
\}  
byte\[\] b = new byte\[count\];  
in.read(b);

//v3.0  
int count = 0;  
while (count == 0) \{  
count = in.available();  
\}  
byte\[\] b = new byte\[count\];  
int readCount = 0; // 已经成功读取的字节的个数  
while (readCount < count) \{  
readCount += in.read(bytes, readCount, count - readCount);  
\}

InputStream in = entity.getContent();//entity是请求数据时获取来的HttpEntity实例  
ByteArrayOutputStream out = new ByteArrayOutputStream();  
byte\[\] cache = new byte\[1024\];  
int nRead = 0;  
while ((nRead = in.read(cache)) != -1) \{  
out.write(cache, 0, nRead);  
out.flush();  
\}  
out.close();  
in.close();  
byte\[\] mBytes = out.toByteArray();

CloseableHttpClient httpClient = HttpClientBuilder.create().build();  
HttpGet httpGet = new HttpGet(path);  
CloseableHttpResponse resp = httpClient.execute(httpGet);// 调用服务器接口  
HttpEntity entity = resp.getEntity();  
InputStream in = entity.getContent();  
ByteArrayOutputStream out = new ByteArrayOutputStream();  
byte\[\] cache = new byte\[1024\];  
int nRead = 0;  
while ((nRead = in.read(cache)) != -1) \{  
out.write(cache, 0, nRead);  
out.flush();  
\}

[java InputStream_ - java_ - ITeye]: https://www.iteye.com/blog/cuisuqiang-1434416
[inputstream.available]: https://blog.sina.com.cn/s/blog_8d365f64010128pb.html