Java 杂记

 

文件拷贝两种方式

//不断内存拷贝，大文件增加cpu负担
public static void copyFile(String srcFile, String destFile) throws Exception {
    byte[] temp = new byte[1024];
    FileInputStream in = new FileInputStream(srcFile);
    FileOutputStream out = new FileOutputStream(destFile);
    int length;
    while ((length = in.read(temp)) != -1) {
        out.write(temp, 0, length);
    }
    in.close();
    out.close();
}
//减少内存拷贝
public static void copyFileWithFileChannel(String srcFileName, String destFileName) throws Exception {
    RandomAccessFile srcFile = new RandomAccessFile(srcFileName, "r");
    FileChannel srcFileChannel = srcFile.getChannel();
    RandomAccessFile destFile = new RandomAccessFile(destFileName, "rw");
    FileChannel destFileChannel = destFile.getChannel();
    long position = 0;
    long count = srcFileChannel.size();
    srcFileChannel.transferTo(position, count, destFileChannel);
}

 ### 查看java进程的GC堆内存信息
```
idea运行的程序使用的是内置jvm,要cmd运行程序或服务器程序：
1. 找到进程ID: ps -ef|grep java
2.jmap -heap 32643
```
```
JVM version is 25.73-b02

using thread-local object allocation.
Parallel GC with 4 thread(s)

Heap Configuration:
   MinHeapFreeRatio         = 0
   MaxHeapFreeRatio         = 100
   MaxHeapSize              = 2099249152 (2002.0MB)
   NewSize                  = 44040192 (42.0MB)
   MaxNewSize               = 699400192 (667.0MB)
   OldSize                  = 88080384 (84.0MB)
   NewRatio                 = 2
   SurvivorRatio            = 8
   MetaspaceSize            = 21807104 (20.796875MB)
   CompressedClassSpaceSize = 1073741824 (1024.0MB)
   MaxMetaspaceSize         = 17592186044415 MB
   G1HeapRegionSize         = 0 (0.0MB)

Heap Usage:
PS Young Generation
Eden Space:
   capacity = 24641536 (23.5MB)
   used     = 4691056 (4.4737396240234375MB)
   free     = 19950480 (19.026260375976562MB)
   19.037189889461438% used
From Space:
   capacity = 524288 (0.5MB)
   used     = 32768 (0.03125MB)
   free     = 491520 (0.46875MB)
   6.25% used
To Space:
   capacity = 524288 (0.5MB)
   used     = 0 (0.0MB)
   free     = 524288 (0.5MB)
   0.0% used
PS Old Generation
   capacity = 47185920 (45.0MB)
   used     = 16827568 (16.048019409179688MB)
   free     = 30358352 (28.951980590820312MB)
   35.662265353732636% used
```

```
将jar添加到本地仓库的做法：
以下面pom.xml依赖的jar包为例：

实际项目中pom.xml依赖写法：

[html] view plain copy
<dependency>  
    <groupId>org.springframework</groupId>  
    <artifactId>spring-context-support</artifactId>  
    <version>3.1.0.RELEASE</version>  
</dependency>  
Maven 安装 JAR 包的命令是：


[html] view plain copy
mvn install:install-file   
-Dfile=jar包的位置   
-DgroupId=上面的groupId   
-DartifactId=上面的artifactId   
-Dversion=上面的version   
-Dpackaging=jar  
例如我的这个spring-context-support-3.1.0.RELEASE.jar 文件放在了"D:\mvn\"中

则命令为：

mvn install:install-file
-Dfile=D:\mvn\spring-context-support-3.1.0.RELEASE.jar

-DgroupId=org.springframework

-DartifactId=spring-context-support

-Dversion=3.1.0.RELEASE

-Dpackaging=jar
```
```
maven 打包  跳过测试
mvn clean package appassembler:generate-daemons -Dmaven.test.skip=true
上传服务器
scp -r target/generate-resource/....        flk@192.168.1.1:/root/kms/
```