Java的try-resource

原来是这个，这个是之前的try catch，包括最后进行关流等操作。

  private String getBodyString(final ServletRequest request) throws IOException {
        StringBuilder sb = new StringBuilder();
        InputStream inputStream = null;
        BufferedReader reader = null;
        try {
            inputStream = cloneInputStream(request.getInputStream());
            reader = new BufferedReader(new InputStreamReader(inputStream, Charset.forName("UTF-8")));
            String line = "";
            while ((line = reader.readLine()) != null) {
                sb.append(line);
            }
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            if (inputStream != null) {
                inputStream.close();
            }
            if (reader!=null){
                reader.close();
            }
        }
        return sb.toString();
    }

JDK7新增的try-with-resource可以改善这一写法

    private String getBodyString(final ServletRequest request) throws IOException {
        var sb = new StringBuilder();
        try (
                var inputStream = request.getInputStream();
                var reader = new BufferedReader(new InputStreamReader(inputStream, StandardCharsets.UTF_8));
        ) {
            var line = "";
            while ((line = reader.readLine()) != null) {
                sb.append(line);
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
        return sb.toString();
    }

而try-with-resource则只是语法糖
实际编译上面代码后：
可以看到高亮行进行了关流

private String getBodyString(ServletRequest request) throws IOException {
        StringBuilder sb = new StringBuilder();

        try {
            ServletInputStream inputStream = request.getInputStream();

            try {
                BufferedReader reader = new BufferedReader(new InputStreamReader(inputStream, StandardCharsets.UTF_8));

                try {
                    String line = "";

                    while((line = reader.readLine()) != null) {
                        sb.append(line);
                    }
                } catch (Throwable var9) {
                    try {
                        reader.close();
                    } catch (Throwable var8) {
                        var9.addSuppressed(var8);
                    }

                    throw var9;
                }

                reader.close();
            } catch (Throwable var10) {
                if (inputStream != null) {
                    try {
                        inputStream.close();
                    } catch (Throwable var7) {
                        var10.addSuppressed(var7);
                    }
                }

                throw var10;
            }

            if (inputStream != null) {
                inputStream.close();
            }
        } catch (IOException var11) {
            var11.printStackTrace();
        }

        return sb.toString();
    }