[Code optimization highlights]

This essay reference many materials, and under validated before or transcriptions or extract or combination with their own experience.

References:

1，SornaQube

2，

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1, equals the string comparison, initiate a text string is determined, on the left, can be prevented NullPointerException

        String successFlag = null;
        if("0".equals(successFlag )){
            //TODO
        }

2, nested if, for, while and try not to sentence structure more than three layers, if more than consider the business logic optimization

IF (condition1) {                   // first layer -OK. 1 
  / * ... * / 
  IF (condition2 The) {                 // layer -OK 2 
    / * ... * / 
    for ( int I = 0; I <10; I ++ ) {   // layer 3 -ok, does not exceed the defined 
      / * ... * / 
      IF (condition4) {             // layer 4 - not ok, beyond the limited 
        / * ... * / 
        return ; 
      } 
    } 
  } 
}

3, (for example: files, database connections, network connections, etc.) relates to the operation of external resources, generally external plate processing resources in the finally closed, after which JDK7 use try-with-resources simplify the code syntax

【未使用try-with-resources】
    FileInputStream inputStream = null;
    try {
        inputStream = new FileInputStream(new File("test"));
        System.out.println(inputStream.read());
    } catch (IOException e) {
        throw new RuntimeException(e.getMessage(), e);
    } finally {
        if (inputStream != null) {
            try {
                inputStream.close();
            } catch (IOException e) {
                throw new RuntimeException(e.getMessage(), e);
            }
        }
    }
【使用try-with-resources】
    try (FileInputStream inputStream = new FileInputStream(new File("test"))) {
        System.out.println(inputStream.read());
    } catch (IOException e) {
        throw new RuntimeException(e.getMessage(), e);
    }

4, connected to a case of: If you have closed external resources when not easy try-with-resources operations grammar, it is recommended to separate try-catch resources

        InputStream inStream = null, fileInStream = null;
        ServletOutputStream outStream = null;
        int byteRead;
        try {
            fileInStream = new FileInputStream("filename");
            inStream = new BufferedInputStream(fileInStream);
            response.reset();
            response.setContentType("APPLICATION/OCTET-STREAM");
            response.setHeader("Content-disposition", "attachment; filename=" + "filename"+ ".xls");
            outStream = response.getOutputStream();
            byte[] buffer = new byte[1024];
            while ((byteRead = inStream.read(buffer)) != -1) {
                outStream.write(buffer, 0, byteRead);
            }
            response.flushBuffer();
            outStream.close();
            inStream.close();
            fileInStream.close();
        } catch (Exception e) {
            LOGGER.error("e);
        }finally{
            try {
                if(outStream!=null){
                    outStream.close();
                }
            } catch (IOException e2) {
                LOGGER.error(e2);
            }
            try {
                if(inStream!=null){
                    inStream.close();
                }
            } catch (IOException e2) {
                LOGGER.error(e2);
            }
            try {
                if(fileInStream!=null){
                    fileInStream.close();
                }
            } catch (IOException e2) {
                LOGGER.error(e2);
            }
        }

5，

Reproduced in: https: //www.cnblogs.com/ruanian/p/11064539.html