使用运行时。exec(字符串命令)在单独的进程中启动JVM。

Another technique here is to introduce additional code into the (hopefully small number of) places where the logic does the System.exit(). This additional code then avoids doing the System.exit() when the logic is being called as part of unit test. For example, define a package private constant like TEST_MODE which is normally false. Then have the unit test code set this true and add logic to the code under test to check for that case and bypass the System.exit call and instead throw an exception that the unit test logic can catch. By the way, in 2021 and using something like spotbugs, this problem can manifest itself in the obscure error that "java.io.IOException: An existing connection was forcibly closed by the remote host".

SecurityManager解决方案有一个小问题。一些方法，如JFrame。exitOnClose，也调用SecurityManager.checkExit。在我的应用程序中，我不希望这个调用失败，所以我使用了

Class[] stack = getClassContext();
if (stack[1] != JFrame.class && !okToExit) throw new ExitException();
super.checkExit(status);

为了让VonC在JUnit 4上运行，我修改了如下代码

protected static class ExitException extends SecurityException {
    private static final long serialVersionUID = -1982617086752946683L;
    public final int status;

    public ExitException(int status) {
        super("There is no escape!");
        this.status = status;
    }
}

private static class NoExitSecurityManager extends SecurityManager {
    @Override
    public void checkPermission(Permission perm) {
        // allow anything.
    }

    @Override
    public void checkPermission(Permission perm, Object context) {
        // allow anything.
    }

    @Override
    public void checkExit(int status) {
        super.checkExit(status);
        throw new ExitException(status);
    }
}

private SecurityManager securityManager;

@Before
public void setUp() {
    securityManager = System.getSecurityManager();
    System.setSecurityManager(new NoExitSecurityManager());
}

@After
public void tearDown() {
    System.setSecurityManager(securityManager);
}

如何注入一个“ExitManager”到这个方法:

public interface ExitManager {
    void exit(int exitCode);
}

public class ExitManagerImpl implements ExitManager {
    public void exit(int exitCode) {
        System.exit(exitCode);
    }
}

public class ExitManagerMock implements ExitManager {
    public bool exitWasCalled;
    public int exitCode;
    public void exit(int exitCode) {
        exitWasCalled = true;
        this.exitCode = exitCode;
    }
}

public class MethodsCallExit {
    public void CallsExit(ExitManager exitManager) {
        // whatever
        if (foo) {
            exitManager.exit(42);
        }
        // whatever
    }
}

生产代码使用ExitManagerImpl，测试代码使用ExitManagerMock，可以检查是否调用了exit()以及使用哪个退出代码。

可以使用java SecurityManager防止当前线程关闭java虚拟机。下面的代码应该是你想要的:

SecurityManager securityManager = new SecurityManager() {
    public void checkPermission(Permission permission) {
        if ("exitVM".equals(permission.getName())) {
            throw new SecurityException("System.exit attempted and blocked.");
        }
    }
};
System.setSecurityManager(securityManager);