2020-09-10 java 编程规范解读

java 编程规范解读

1. try catch

finally 块必须对资源对象、流对象进行关闭，有异常也要做 try-catch。
说明：如果 JDK7 及以上，可以使用 try-with-resources 方式。

2. JDK7 特性之 try-with-resource 资源的自动管理

该try-with资源语句是try声明了一个或多个资源声明。一个资源是程序与它完成后，必须关闭的对象。该try-with资源语句确保每个资源在发言结束时关闭。

任何实现的java.lang.AutoCloseable对象（包括实现的所有对象）java.io.Closeable都可以用作资源。

  @Test
    public void test2() throws IOException {
        String filepath = "D:\\gui-config.json";

        try (
                FileReader fileReader = new FileReader(filepath);
                BufferedReader br = new BufferedReader(fileReader)
        ) {
            String curline = null;
            while ((curline = br.readLine()) != null) {
                System.out.println(curline);
            }
        }

    }
    // FileReader 和 BufferedReader 均实现了 AutoCloseable 接口
    

FileReader Closeable

// extends InputStreamReader
public class FileReader extends InputStreamReader
// InputStreamReader extends Reader
public class InputStreamReader extends Reader 
// Reader implements Readable, Closeable
public abstract class Reader implements Readable, Closeable     

BufferReader

// extends Reader 
public class BufferedReader extends Reader 
// Reader implements Readable, Closeable
public abstract class Reader implements Readable, Closeable   

3. 自定义 AutoCloseable 实现类

3.1 自定义自动关闭类AutoCloseDemo

package core.java.autoclosable;

/**
 * @ClassName AutoCloseTest
 * @description: 自定义自动关闭类；
 * @author: peiwisdom
 * @create: 2020-09-10 17:49
 **/
public class AutoCloseDemo implements AutoCloseable{

    @Override
    public void close() throws Exception {
        System.out.println("关闭");
    }

    public void run(boolean flag) {
        if (flag) {
            System.out.println("业务处理");
        } else {
            System.out.println("出现异常");
            throw new RuntimeException("自定义RuntimeException");
        }
    }
}

3.2 测试类

package core.java.autoclosable;

import org.junit.Test;

/**
 * @ClassName AutoCloseDemoTest
 * @description: 自动关闭测试
 * @author: peiwisdom
 * @create: 2020-09-10 17:54
 **/
public class AutoCloseDemoTest {
    @Test
    public void test3() throws Exception {
        try (AutoCloseDemo autoCloseTestModel = new AutoCloseDemo()) {
            autoCloseTestModel.run(false);
        }
    }

}

3.3 执行结果

"C:\Program Files\Java\jdk1.8.0_251\bin\java.exe" -ea -Didea.test.cyclic.buffer.size=1048576 "-javaagent:C:\Program Files\JetBrains\IntelliJ IDEA 2020.1.2\lib\idea_rt.jar=58651:C:\Program Files\JetBrains\IntelliJ IDEA 2020.1.2\bin" -Dfile.encoding=UTF-8 -classpath "C:\Program Files\JetBrains\IntelliJ IDEA 2020.1.2\lib\idea_rt.jar;C:\Program Files\JetBrains\IntelliJ IDEA 2020.1.2\plugins\junit\lib\junit5-rt.jar;C:\Program Files\JetBrains\IntelliJ IDEA 2020.1.2\plugins\junit\lib\junit-rt.jar;C:\Program Files\Java\jdk1.8.0_251\jre\lib\charsets.jar;C:\Program Files\Java\jdk1.8.0_251\jre\lib\deploy.jar;C:\Program Files\Java\jdk1.8.0_251\jre\lib\ext\access-bridge-64.jar;C:\Program Files\Java\jdk1.8.0_251\jre\lib\ext\cldrdata.jar;C:\Program Files\Java\jdk1.8.0_251\jre\lib\ext\dnsns.jar;C:\Program Files\Java\jdk1.8.0_251\jre\lib\ext\jaccess.jar;C:\Program Files\Java\jdk1.8.0_251\jre\lib\ext\jfxrt.jar;C:\Program Files\Java\jdk1.8.0_251\jre\lib\ext\localedata.jar;C:\Program Files\Java\jdk1.8.0_251\jre\lib\ext\nashorn.jar;C:\Program Files\Java\jdk1.8.0_251\jre\lib\ext\sunec.jar;C:\Program Files\Java\jdk1.8.0_251\jre\lib\ext\sunjce_provider.jar;C:\Program Files\Java\jdk1.8.0_251\jre\lib\ext\sunmscapi.jar;C:\Program Files\Java\jdk1.8.0_251\jre\lib\ext\sunpkcs11.jar;C:\Program Files\Java\jdk1.8.0_251\jre\lib\ext\zipfs.jar;C:\Program Files\Java\jdk1.8.0_251\jre\lib\javaws.jar;C:\Program Files\Java\jdk1.8.0_251\jre\lib\jce.jar;C:\Program Files\Java\jdk1.8.0_251\jre\lib\jfr.jar;C:\Program Files\Java\jdk1.8.0_251\jre\lib\jfxswt.jar;C:\Program Files\Java\jdk1.8.0_251\jre\lib\jsse.jar;C:\Program Files\Java\jdk1.8.0_251\jre\lib\management-agent.jar;C:\Program Files\Java\jdk1.8.0_251\jre\lib\plugin.jar;C:\Program Files\Java\jdk1.8.0_251\jre\lib\resources.jar;C:\Program Files\Java\jdk1.8.0_251\jre\lib\rt.jar;D:\open-source\graphresolvedesignpartner\target\test-classes;D:\open-source\graphresolvedesignpartner\target\classes;C:\Users\peizihui\.m2\repository\junit\junit\4.10\junit-4.10.jar;C:\Users\peizihui\.m2\repository\org\hamcrest\hamcrest-core\1.1\hamcrest-core-1.1.jar" com.intellij.rt.junit.JUnitStarter -ideVersion5 -junit4 core.java.autoclosable.AutoCloseDemoTest,test3
出现异常
关闭

java.lang.RuntimeException: 自定义RuntimeException

    at core.java.autoclosable.AutoCloseDemo.run(AutoCloseDemo.java:21)
    at core.java.autoclosable.AutoCloseDemoTest.test3(AutoCloseDemoTest.java:15)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:498)
    at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:45)
    at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:15)
    at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:42)
    at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:20)
    at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:263)
    at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:68)
    at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:47)
    at org.junit.runners.ParentRunner$3.run(ParentRunner.java:231)
    at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:60)
    at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:229)
    at org.junit.runners.ParentRunner.access$000(ParentRunner.java:50)
    at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:222)
    at org.junit.runners.ParentRunner.run(ParentRunner.java:300)
    at org.junit.runner.JUnitCore.run(JUnitCore.java:157)
    at com.intellij.junit4.JUnit4IdeaTestRunner.startRunnerWithArgs(JUnit4IdeaTestRunner.java:68)
    at com.intellij.rt.junit.IdeaTestRunner$Repeater.startRunnerWithArgs(IdeaTestRunner.java:33)
    at com.intellij.rt.junit.JUnitStarter.prepareStreamsAndStart(JUnitStarter.java:230)
    at com.intellij.rt.junit.JUnitStarter.main(JUnitStarter.java:58)


Process finished with exit code -1

4. 参考

https://docs.oracle.com/javase/tutorial/essential/exceptions/tryResourceClose.html