优化前端资源加载

水深无声 2022-12-18 01:53 192阅读 0赞

## 一、优化前端资源加载 ##

`js`加载资源方式：  
1.1、使用内联图片，也就是将图片转换为base64编码的data-url。这种方式，其实是将图片的信息集成到css文件中，避免了图片资源的单独加载。但图片内联会增加css文件的大小，增加首屏渲染的时间。

1.2、使用js代码对图片进行预加载。

preloadImage() { 
        const imgList = [
            require('@/assets/imgs/error.png'),
            require('@/assets/imgs/ticket_bg.png')
        ];
        for (let i = 0; i < imgList.length; i++) { 
            const newIMG = new Image();
            newIMG.src = imgList[i];
        }
    }

1.3、`preload/prefetch`，它们能够辅助浏览器优化资源加载的顺序和时机，提升页面性能

<head>
        ...
        <link rel="preload" as="font" href="<%= require('/assets/fonts/AvenirNextLTPro-Demi.otf') %>" crossorigin>
        <link rel="preload" as="font" href="<%= require('/assets/fonts/AvenirNextLTPro-Regular.otf') %>" crossorigin>
        ...
    </head>

const PreloadWebpackPlugin = require('preload-webpack-plugin');
    ...
    plugins: [
      new PreloadWebpackPlugin({ 
        rel: 'preload'，
        as(entry) {   //资源类型
          if (/\.css$/.test(entry)) return 'style';
          if (/\.woff$/.test(entry)) return 'font';
          if (/\.png$/.test(entry)) return 'image';
          return 'script';
        },
        include: 'asyncChunks', // preload模块范围，还可取值'initial'|'allChunks'|'allAssets',
        fileBlacklist: [/\.svg/] // 资源黑名单
        fileWhitelist: [/\.script/] // 资源白名单
      })
    ]

二、OCR工具类

import java.io.ByteArrayInputStream;
    import java.io.ByteArrayOutputStream;
    import java.io.IOException;
    import java.util.HashMap;
    
    import javax.imageio.ImageIO;
    
    import org.json.JSONObject;
    import org.jsoup.Jsoup;
    import org.spiderflow.ocr.model.Ocr;
    
    import com.baidu.aip.ocr.AipOcr;
    
    public class OcrUtil { 
    	
    	private static HashMap<String, AipOcr> aipOcrMap = new HashMap<String, AipOcr>();
    	
    	private static HashMap<String, String> options = new HashMap<String, String>();
    	
    	private static class ErrorCode { 
    		
    		/** * 图片格式不对 */
    		private static final int IMAGE_FORMAT_ERROR = 216201;
    		
    		/** * 响应无效 */
    		private static final int URL_RESPONSE_INVALID = 282113;
    		
    	}
    	
    	static { 
    	    options.put("detect_direction", "true");
    	    options.put("detect_language", "true");
    	    options.put("probability", "true");
    	}
    	
    	public static AipOcr getAipOcr(Ocr ocr) { 
    		String ocrMapKey = ocr.getAppId()+ocr.getApiKey()+ocr.getSecretKey();
    		AipOcr aipOcr = aipOcrMap.get(ocrMapKey);
    		if(aipOcr == null) { 
    			aipOcr = new AipOcr(ocr.getAppId(), ocr.getApiKey(), ocr.getSecretKey());
    			aipOcrMap.put(ocrMapKey, aipOcr);
    		}
    		return aipOcr;
    	}
    	
    	public static int getErrorCode(JSONObject bgJson) { 
    		if(!bgJson.isNull("error_code")) { 
    			int errorCode = bgJson.getInt("error_code");
    			return errorCode;
    		}
    		return -996;
    	}
    	
    	public static boolean isImageFormatError(int errorCode) { 
    		if(errorCode != -996) { 
    			// 图片格式不对
    			if(errorCode == ErrorCode.IMAGE_FORMAT_ERROR) { 
    				return true;
    			}
    		}
    		return false;
    	}
    	
    	public static boolean isUrlResponseInvalid(int errorCode) { 
    		if(errorCode != -996) { 
    			if(errorCode == ErrorCode.URL_RESPONSE_INVALID) { 
    				return true;
    			}
    		}
    		return false;
    	}
    	
    	public static byte[] imgConvert(byte[] bytes) throws IOException { 
    		ByteArrayOutputStream output = new ByteArrayOutputStream();
    		ByteArrayInputStream input = new ByteArrayInputStream(bytes);
    		ImageIO.write(ImageIO.read(input), "png", output);
    		return output.toByteArray();
    	}
    	
    	public static JSONObject ocrIdentify(Ocr ocr,byte[] bytes) throws Exception { 
    		try { 
    			AipOcr aipOcr = getAipOcr(ocr);
    			JSONObject bgJson = aipOcr.basicGeneral(bytes, options);
    			if(isImageFormatError(getErrorCode(bgJson))) { 
    				return aipOcr.basicGeneral(imgConvert(bytes), options);
    			}
    			return bgJson;
    		} catch (Exception e) { 
    			throw e;
    		}
    	}
    	
    	public static JSONObject ocrIdentify(Ocr ocr,String url) throws IOException { 
    		AipOcr aipOcr = getAipOcr(ocr);
    		JSONObject bgJson = aipOcr.basicGeneralUrl(url, options);
    		if(isUrlResponseInvalid(getErrorCode(bgJson))) { 
    			return aipOcr.basicGeneral(imgConvert(Jsoup.connect(url).ignoreContentType(true).execute().bodyAsBytes()), options);
    		}
    		return bgJson;
    	}
    	
    }

三、下划线互转驼峰

import java.util.Arrays;
    import java.util.List;
    import java.util.regex.Matcher;
    import java.util.regex.Pattern;
    import java.util.stream.Collectors;
    
    public class FieldUtils { 
    
        private static Pattern humpPattern = Pattern.compile("[A-Z]");
    
        public static List<String> allFields(Class clazz){ 
            return Arrays.stream(clazz.getDeclaredFields()).map(item->humpToLine2(item.getName())).collect(Collectors.toList());
        }
    
        public static List<String> updateFields(Class clazz){ 
            return Arrays.stream(clazz.getDeclaredFields())
                    .filter(item->item.getAnnotation(ApiUpdateField.class) != null)
                    .map(item-> humpToLine2(item.getName())).collect(Collectors.toList());
        }
    
        /** * 下划线转驼峰 */
        public static String underlineToCamel(String name){ 
            StringBuilder sb = new StringBuilder(name.length());
            for (int i = 0; i < name.length(); i++) { 
                char c = name.charAt(i);
                if ('_' == c) { 
                    if (++i < name.length()){ 
                        sb.append(Character.toUpperCase(name.charAt(i)));
                    }
                }else { 
                    sb.append(c);
                }
            }
            return sb.toString();
        }
    
        /** * 驼峰转下划线 */
        public static String humpToLine2(String str) { 
            Matcher matcher = humpPattern.matcher(str);
            StringBuffer sb = new StringBuffer();
            while (matcher.find()) { 
                matcher.appendReplacement(sb, "_" + matcher.group(0).toLowerCase());
            }
            matcher.appendTail(sb);
            return sb.toString();
        }
    }

import java.lang.annotation.ElementType;
    import java.lang.annotation.Retention;
    import java.lang.annotation.RetentionPolicy;
    import java.lang.annotation.Target;
    
    @Target(ElementType.FIELD)
    @Retention(RetentionPolicy.RUNTIME)
    public @interface ApiUpdateField { 
    }

四、表结构解析

import java.util.ArrayList;
    import java.util.List;
    import java.util.Scanner;
    import java.util.regex.Matcher;
    import java.util.regex.Pattern;
    
    /** * 表结构解析 */
    public class SqlUtils { 
        public static String getByPattern(String sql, String pattern, int group) { 
            Pattern compile = Pattern.compile(pattern);
            Matcher matcher = compile.matcher(sql);
            while (matcher.find()) { 
                return matcher.group(group);
            }
            return null;
        }
    
        public static List<String> getColumnSqls(String sql) { 
            List<String> lines = new ArrayList<>();
            Scanner scanner = new Scanner(sql);
            boolean start = false;
            while (scanner.hasNextLine()) { 
                String nextLine = scanner.nextLine();
                if (nextLine.indexOf("CREATE TABLE") != -1) { 
                    start = true;
                    continue;
                }
                if (nextLine.indexOf("PRIMARY KEY") != -1 || nextLine.indexOf("ENGINE=") != -1) { 
                    start = false;
                    continue;
                }
                if (start) { 
                    lines.add(nextLine);
                }
            }
            return lines;
        }
    }