java基础---->Runtime类的使用(一)

　　这里面我们对java中的Runtime类做一个简单的了解介绍。若不常想到无常和死，虽有绝顶的聪明，照理说也和呆子一样。

Runtimeo类的使用

一、得到系统内存的一些信息

@Test
public void runtimeInfo() {
Runtime runtime = Runtime.getRuntime();
int processors = runtime.availableProcessors();
long freeMemory = runtime.freeMemory();
long maxMemory = runtime.maxMemory();
long totalMemory = runtime.totalMemory();

// processors=4, freeMemory=165713400, maxMemory=2837446656, totalMemory=192937984
logger.debug("processors={}, freeMemory={}, maxMemory={}, totalMemory={}", processors, freeMemory, maxMemory, totalMemory);
}

二、得到系统的环境变量

@Test
public void dirRuntimeProcess() throws IOException, InterruptedException {
Process process = Runtime.getRuntime().exec("cmd.exe /c echo %JAVA_HOME%");
BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(process.getInputStream()));

String string = null;
while ((string = bufferedReader.readLine()) != null) {
System.out.println(string); // D:\Java\jdk\jdk1.8.0_152
}
process.waitFor();
System.out.println("return: " + process.exitValue()); // return: 0
}

三、得到java的版本号，这个和上述的不一样

@Test
public void getJavaVersion() {
try {
Process process = Runtime.getRuntime().exec("javac -version");
BufferedReader br = new BufferedReader(new InputStreamReader(process.getErrorStream()));
String line = null;
while ((line = br.readLine()) != null)
System.out.println(line); // javac 1.8.0_152
process.waitFor();
System.out.println("Process exitValue: " + process.exitValue());
} catch (Throwable t) {
t.printStackTrace();
}
}

四、执行外部命令得到的结果

@Test
public void execProgramC() {
try {
Process process = Runtime.getRuntime().exec("C:/Users/76801/Desktop/huhx.exe");
BufferedReader br = new BufferedReader(new InputStreamReader(process.getInputStream()));
String line = null;
while ((line = br.readLine()) != null)
System.out.println(line); // Hello World.
process.waitFor();
System.out.println("Process exitValue: " + process.exitValue());
} catch (Throwable t) {
t.printStackTrace();
}
}

huhx.c比较简单，就是打印一句话。

#include<stdio.h>

void main() {
printf("Hello World.");
}

五、使用Runtime类导出mysql脚本

@Test
public void execMysqldump() throws IOException, InterruptedException {
String execCommand = "cmd c/ D:/Java/mysqldump.exe -uhuhx -phuhx boot_learn > D:/bootlearn.sql";
System.out.println("exec command: " + execCommand);
Runtime runtime = Runtime.getRuntime();
Process p = runtime.exec(execCommand);
StreamGobbler errorGobbler = new StreamGobbler(p.getErrorStream(), "Error");
StreamGobbler outputGobbler = new StreamGobbler(p.getInputStream(), "Output");
errorGobbler.start();
outputGobbler.start();
p.waitFor();
System.out.println("successful." + p.exitValue());
}

上述也使用到了网上所说的读出窗口的标准输出缓冲区中的内容，仍旧没有解决Process的waitFor阻塞问题。下面是清空缓冲区的线程代码：

public class StreamGobbler extends Thread {

InputStream is;
String type;

public StreamGobbler(InputStream is, String type) {
this.is = is;
this.type = type;
}

public void run() {
try (InputStreamReader isr = new InputStreamReader(is);) {
BufferedReader br = new BufferedReader(isr);
String line = null;
while ((line = br.readLine()) != null) {
if (type.equals("Error")) {
System.out.println("Error   :" + line);
} else {
System.out.println("Debug:" + line);
}
}
} catch (IOException e) {
e.printStackTrace();
}
}
}

代码的目标是导出mysql数据库的脚本。没有找到问题的解决方案，运行环境是win10，jdk1.8。

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