1.26学习笔记

电玩女神 2022-08-06 13:07 115阅读 0赞

一、 ndk异常捕捉（http://blog.csdn.net/xyang81/article/details/42319789）

anr无响应异常查看方法:

在/data/anr目录下生成一个traces.txt文件，记录系统产生anr异常的堆栈和线程信息

如果是ndk闪退，可以使用上面链接的方法1查看，也是比较简单的一种查看方法：

假设log闪退打印如下信息：

01-01 17:59:38.596: I/DEBUG(253):     \#04  pc 00000cf4  /data/app-lib/com.example.hellojni-1/libhello-jni.so (willCrash+32)  
01-01 17:59:38.596: I/DEBUG(253):     \#05  pc 00000d1c  /data/app-lib/com.example.hellojni-1/libhello-jni.so (JNI\_OnLoad+20)

我们先记录下让程序崩溃的汇编指令地址，willCrash：00000cf4，JNI\_OnLoad：00000d1c

**方式1：使用arm-linux-androideabi-addr2line  定位出错位置**  
以arm架构的CPU为例，执行如下命令：

**\[cpp\]**  [view plain][] [copy][view plain] [![在CODE上查看代码片][CODE]][CODE_CODE] [![派生到我的代码片][ico_fork.svg]][ico_fork.svg 1]

1.  /Users/yangxin/Documents/devToos/java/android-ndk-r9d/toolchains/arm-linux-androideabi-4.8/prebuilt/darwin-x86\_64/bin/arm-linux-androideabi-addr2line -e /Users/yangxin/Documents/devToos/java/android-ndk-r9d/samples/hello-jni/obj/local/armeabi-v7a/libhello-jni.so 00000cf4 00000d1c

\-e：指定so文件路径

0000cf4 0000d1c：出错的汇编指令地址

结果如下：

![SouthEast][]

是不是惊喜的看到我们想要的结果了，分别在hello-jni.c的10和15行的出的错，再回去看看hello-jni.c的源码，15行的Jni\_OnLoad函内调用了willCrash函数，第10行做了除0的操作引发的crash。

二、java常用代码：

文件追加字符串：

BufferedWriter out = null;    
try \{    
    out = new BufferedWriter(new FileWriter(”filename”, true));    
    out.write(”aString”);    
\} catch (IOException e) \{    
    // error processing code    
\} finally \{    
    if (out != null) \{    
        out.close();    
    \}    
\}

nio开速文件拷贝

public static void fileCopy( File in, File out )    
            throws IOException    
    \{    
        FileChannel inChannel = new FileInputStream( in ).getChannel();    
        FileChannel outChannel = new FileOutputStream( out ).getChannel();    
        try   
        \{    
//          inChannel.transferTo(0, inChannel.size(), outChannel);      // original -- apparently has trouble copying large files on Windows    
    
            // magic number for Windows, 64Mb - 32Kb)    
            int maxCount = (64 \* 1024 \* 1024) - (32 \* 1024);    
            long size = inChannel.size();    
            long position = 0;    
            while ( position < size )    
            \{    
               position += inChannel.transferTo( position, maxCount, outChannel );    
            \}    
        \}    
        finally   
        \{    
            if ( inChannel != null )    
            \{    
               inChannel.close();    
            \}    
            if ( outChannel != null )    
            \{    
                outChannel.close();    
            \}    
        \}    
    \}

itext jar 生成pdf

import java.io.File;    
import java.io.FileOutputStream;    
import java.io.OutputStream;    
import java.util.Date;    
    
import com.lowagie.text.Document;    
import com.lowagie.text.Paragraph;    
import com.lowagie.text.pdf.PdfWriter;    
    
public class GeneratePDF \{    
    
    public static void main(String\[\] args) \{    
        try \{    
            OutputStream file = new FileOutputStream(new File("C:\\\\Test.pdf"));    
    
            Document document = new Document();    
            PdfWriter.getInstance(document, file);    
            document.open();    
            document.add(new Paragraph("Hello Kiran"));    
            document.add(new Paragraph(new Date().toString()));    
    
            document.close();    
            file.close();    
    
        \} catch (Exception e) \{    
    
            e.printStackTrace();    
        \}    
    \}    
\}

http代理设置：

System.getProperties().put("http.proxyHost", "someProxyURL");    
System.getProperties().put("http.proxyPort", "someProxyPort");    
System.getProperties().put("http.proxyUser", "someUserName");    
System.getProperties().put("http.proxyPassword", "somePassword");

另一种单例：

public enum SimpleSingleton \{    
    INSTANCE;    
    public void doSomething() \{    
    \}    
\}    
    
//Call the method from Singleton:    
SimpleSingleton.INSTANCE.doSomething();

创建zip，jar

<span style="font-family:Arial;font-size:14px;">import java.util.zip.\*;    
import java.io.\*;    
    
public class ZipIt \{    
    public static void main(String args\[\]) throws IOException \{    
        if (args.length < 2) \{    
            System.err.println("usage: java ZipIt Zip.zip file1 file2 file3");    
            System.exit(-1);    
        \}    
        File zipFile = new File(args\[0\]);    
        if (zipFile.exists()) \{    
            System.err.println("Zip file already exists, please try another");    
            System.exit(-2);    
        \}    
        FileOutputStream fos = new FileOutputStream(zipFile);    
        ZipOutputStream zos = new ZipOutputStream(fos);    
        int bytesRead;    
        byte\[\] buffer = new byte\[1024\];    
        CRC32 crc = new CRC32();    
        for (int i=1, n=args.length; i < n; i++) \{    
            String name = args\[i\];    
            File file = new File(name);    
            if (!file.exists()) \{    
                System.err.println("Skipping: " + name);    
                continue;    
            \}    
            BufferedInputStream bis = new BufferedInputStream(    
                new FileInputStream(file));    
            crc.reset();    
            while ((bytesRead = bis.read(buffer)) != -1) \{    
                crc.update(buffer, 0, bytesRead);    
            \}    
            bis.close();    
            // Reset to beginning of input stream    
            bis = new BufferedInputStream(    
                new FileInputStream(file));    
            ZipEntry entry = new ZipEntry(name);    
            entry.setMethod(ZipEntry.STORED);    
            entry.setCompressedSize(file.length());    
            entry.setSize(file.length());    
            entry.setCrc(crc.getValue());    
            zos.putNextEntry(entry);    
            while ((bytesRead = bis.read(buffer)) != -1) \{    
                zos.write(buffer, 0, bytesRead);    
            \}    
            bis.close();    
        \}    
        zos.close();    
    \}    
\} </span>

array转出map

import java.util.Map;    
import org.apache.commons.lang.ArrayUtils;    
    
public class Main \{    
    
  public static void main(String\[\] args) \{    
    String\[\]\[\] countries = \{ \{ "United States", "New York" \}, \{ "United Kingdom", "London" \},    
        \{ "Netherland", "Amsterdam" \}, \{ "Japan", "Tokyo" \}, \{ "France", "Paris" \} \};    
    
    Map countryCapitals = ArrayUtils.toMap(countries);    
    
    System.out.println("Capital of Japan is " + countryCapitals.get("Japan"));    
    System.out.println("Capital of France is " + countryCapitals.get("France"));    
  \}    
\}

反射修改数组大小：

/\*\*   
\* Reallocates an array with a new size, and copies the contents   
\* of the old array to the new array.   
\* @param oldArray  the old array, to be reallocated.   
\* @param newSize   the new array size.   
\* @return          A new array with the same contents.   
\*/   
private static Object resizeArray (Object oldArray, int newSize) \{    
   int oldSize = java.lang.reflect.Array.getLength(oldArray);    
   Class elementType = oldArray.getClass().getComponentType();    
   Object newArray = java.lang.reflect.Array.newInstance(    
         elementType,newSize);    
   int preserveLength = Math.min(oldSize,newSize);    
   if (preserveLength > 0)    
      System.arraycopy (oldArray,0,newArray,0,preserveLength);    
   return newArray;    
\}    
    
// Test routine for resizeArray().    
public static void main (String\[\] args) \{    
   int\[\] a = \{1,2,3\};    
   a = (int\[\])resizeArray(a,5);    
   a\[3\] = 4;    
   a\[4\] = 5;    
   for (int i=0; i<a.length; i++)    
      System.out.println (a\[i\]);    
\}

[view plain]: http://blog.csdn.net/xyang81/article/details/42319789#
[CODE]: https://code.csdn.net/assets/CODE_ico.png
[CODE_CODE]: https://code.csdn.net/snippets/569527
[ico_fork.svg]: https://code.csdn.net/assets/ico_fork.svg
[ico_fork.svg 1]: https://code.csdn.net/snippets/569527/fork
[SouthEast]: /images/20220806/e0ea5722caa8442985522973b30a16a8.png