异常模板代码

看这篇文章：http://tutorials.jenkov.com/java-exception-handling/exception-handling-templates.html

再录一下：

一个异常捕获后，在finally里中再捕获异常，抛出异常会覆盖先前的异常信息，所以需要清晰的判断每个可能的异常，如此不会遗漏被覆盖的异常。如果代码复杂，异常判断是一键冗余的事情，所以会用模板的方式来简化工作，减少出错。

其实就是讲一个共通的代码如何更加优雅的公用。

 Input       input            = null;    IOException PRocessException = null;    try{        input = new FileInputStream(fileName);        //...process input stream...    } catch (IOException e) {        processException = e;    } finally {       if(input != null){          try {             input.close();          } catch(IOException e){             if(processException != null){                throw new MyException(processException, e,                  "Error message..." +                  fileName);             } else {                throw new MyException(e,                    "Error closing InputStream for file " +                    fileName;             }          }       }       if(processException != null){          throw new MyException(processException,            "Error processing InputStream for file " +                fileName;    }

模板模式：

public abstract class InputStreamProcessingTemplate {    public void process(String fileName){        IOException processException = null;        InputStream input = null;        try{            input = new FileInputStream(fileName);            doProcess(input);        } catch (IOException e) {            processException = e;        } finally {           if(input != null){              try {                 input.close();              } catch(IOException e){                 if(processException != null){                    throw new MyException(processException, e,                      "Error message..." +                      fileName);                 } else {                    throw new MyException(e,                        "Error closing InputStream for file " +                        fileName;                 }              }           }           if(processException != null){              throw new MyException(processException,                "Error processing InputStream for file " +                    fileName;        }    }    //override this method in a subclass, to process the stream.    public abstract void doProcess(InputStream input) throws IOException;}

调用：

  new InputStreamProcessingTemplate(){        public void doProcess(InputStream input) throws IOException{            int inChar = input.read();            while(inChar !- -1){                //do something with the chars...            }        }    }.process("someFile.txt");

接口实现的办法：

public interface InputStreamProcessor {    public void process(InputStream input) throws IOException;}public class InputStreamProcessingTemplate {    public void process(String fileName, InputStreamProcessor processor){        IOException processException = null;        InputStream input = null;        try{            input = new FileInputStream(fileName);            processor.process(input);        } catch (IOException e) {            processException = e;        } finally {           if(input != null){              try {                 input.close();              } catch(IOException e){                 if(processException != null){                    throw new MyException(processException, e,                      "Error message..." +                      fileName;                 } else {                    throw new MyException(e,                        "Error closing InputStream for file " +                        fileName);                 }              }           }           if(processException != null){              throw new MyException(processException,                "Error processing InputStream for file " +                    fileName;        }    }}

调用：

new InputStreamProcessingTemplate()        .process("someFile.txt", new InputStreamProcessor(){            public void process(InputStream input) throws IOException{                int inChar = input.read();                while(inChar !- -1){                    //do something with the chars...                }            }        });

静态模板：

public class InputStreamProcessingTemplate {    public static void process(String fileName,    InputStreamProcessor processor){        IOException processException = null;        InputStream input = null;        try{            input = new FileInputStream(fileName);            processor.process(input);        } catch (IOException e) {            processException = e;        } finally {           if(input != null){              try {                 input.close();              } catch(IOException e){                 if(processException != null){                    throw new MyException(processException, e,                      "Error message..." +                      fileName);                 } else {                    throw new MyException(e,                        "Error closing InputStream for file " +                        fileName;                 }              }           }           if(processException != null){              throw new MyException(processException,                "Error processing InputStream for file " +                    fileName;        }    }}

调用：

 InputStreamProcessingTemplate.process("someFile.txt",        new InputStreamProcessor(){            public void process(InputStream input) throws IOException{                int inChar = input.read();                while(inChar !- -1){                    //do something with the chars...                }            }        });