你好我对java有一些疑问。 这是我的代码:
public static void main(String[] args) throws Exception {
Process pr = Runtime.getRuntime().exec("java -version");
BufferedReader in = new BufferedReader(new InputStreamReader(pr.getInputStream()));
String line;
while ((line = in.readLine()) != null) {
System.out.println(line);
}
pr.waitFor();
System.out.println("ok!");
in.close();
System.exit(0);
}
在那个代码我试图获得一个java版本命令执行是好的,但我无法读取输出它只返回null。为什么呢?
答案 0 :(得分:50)
BufferedReader in = new BufferedReader(new InputStreamReader(pr.getErrorStream()));
编辑:
您可以使用ProcessBuilder(并阅读文档)
ProcessBuilder ps=new ProcessBuilder("java.exe","-version");
//From the DOC: Initially, this property is false, meaning that the
//standard output and error output of a subprocess are sent to two
//separate streams
ps.redirectErrorStream(true);
Process pr = ps.start();
BufferedReader in = new BufferedReader(new InputStreamReader(pr.getInputStream()));
String line;
while ((line = in.readLine()) != null) {
System.out.println(line);
}
pr.waitFor();
System.out.println("ok!");
in.close();
System.exit(0);
答案 1 :(得分:9)
请注意,我们正在逐行读取流程输出到StringBuilder
。由于try-with-resources
语句,我们不需要手动关闭流。 ProcessBuilder
类允许我们向其构造函数提交程序名称和参数数量。
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
public class ProcessOutputExample
{
public static void main(String[] arguments) throws IOException,
InterruptedException
{
System.out.println(getProcessOutput());
}
public static String getProcessOutput() throws IOException, InterruptedException
{
ProcessBuilder processBuilder = new ProcessBuilder("java",
"-version");
processBuilder.redirectErrorStream(true);
Process process = processBuilder.start();
StringBuilder processOutput = new StringBuilder();
try (BufferedReader processOutputReader = new BufferedReader(
new InputStreamReader(process.getInputStream()));)
{
String readLine;
while ((readLine = processOutputReader.readLine()) != null)
{
processOutput.append(readLine + System.lineSeparator());
}
process.waitFor();
}
return processOutput.toString().trim();
}
}
打印:
java version "1.8.0_45"
Java(TM) SE Runtime Environment (build 1.8.0_45-b15)
Java HotSpot(TM) 64-Bit Server VM (build 25.45-b02, mixed mode)
答案 2 :(得分:2)
您已拥有process - 对象(名称为pr)。您可以获得Input-,Output-和Errorstream。在您的情况下,您需要pr.getInputStream()。从那里读取,它连接到过程的输出。
答案 3 :(得分:0)
试试这个
public static final Pair<Integer,Integer> javaVersion(File file) throws IOException {
final ProcessBuilder pb = new ProcessBuilder("java", "-version");
pb.directory(new File(file.getCanonicalPath() + File.separator + "bin"));
pb.redirectErrorStream(true);
// Call the test target
final Process process = pb.start();
final InputStream in = process.getInputStream();
final InputStream err = process.getErrorStream();
BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(in,"UTF-8"));
String s = bufferedReader.readLine();
int start = s.indexOf('\"');
int end = s.lastIndexOf('\"');
String substring = s.substring(start + 1, end);
String[] split = substring.split("\\.");
return new Pair<>(Integer.parseInt(split[0]),Integer.parseInt(split[1]));
}
答案 4 :(得分:0)
我也遇到了这个问题,因为我没有正确设置$ JAVA_HOME。 (我忘了目录/首页)。
编辑$ JAVA_HOME之后,更新Gradle JVM,并删除.idea目录以使用gradle重新构建,效果很好。