- 客户端没有执行操作的权限
- 客户端没有访问资源的权限
- 客户端要访问的项目不存在
- 等等 ...

遇到这些情况时，通常要返回 **4XX**（400 至 499）**HTTP 状态码**。

**4XX** 状态码与表示请求成功的 **2XX**（200 至 299） HTTP 状态码类似。

只不过，**4XX** 状态码表示客户端发生的错误。

大家都知道**「404 Not Found」**错误，还有调侃这个错误的笑话吧？

## 使用 `HTTPException`

向客户端返回 HTTP 错误响应，可以使用 `HTTPException`。

### 导入 `HTTPException`

{* ../../docs_src/handling_errors/tutorial001.py hl[1] *}

### 触发 `HTTPException`

// Copyright 2016 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

package tar

import (
	"bytes"
	"fmt"
	"strconv"
	"strings"
	"time"
)

// hasNUL reports whether the NUL character exists within s.
func hasNUL(s string) bool {
	return strings.Contains(s, "\x00")
}

// isASCII reports whether the input is an ASCII C-style string.

	exit_1
fi

sleep 10
./mc admin user svcacct info minio2 testsvc
if [ $? -eq 0 ]; then
	echo "svc account found after delete, exiting.."
	exit_1
fi

./mc admin user svcacct info minio3 testsvc
if [ $? -eq 0 ]; then
	echo "svc account found after delete, exiting.."
	exit_1
fi

# create a bucket bucket2 on minio1.
./mc mb minio1/bucket2

./mc mb minio1/newbucket

	LatestModTime time.Time `msg:"lm"`

	Versions     []FileInfo `msg:"vs"`
	FreeVersions []FileInfo `msg:"fvs"`
}

// findVersionIndex will return the version index where the version
// was found. Returns -1 if not found.
func (f *FileInfoVersions) findVersionIndex(v string) int {
	if f == nil || v == "" {
		return -1
	}
	if v == nullVersionID {
		for i, ver := range f.Versions {
			if ver.VersionID == "" {

            Builder builder = builders.get(builderId);
            if (builder == null) {
                throw new BuilderNotFoundException(
                        String.format("The builder requested using id = %s cannot be" + " found", builderId));
            }

            int degreeOfConcurrency = session.getRequest().getDegreeOfConcurrency();
            if (degreeOfConcurrency > 1) {
                logger.info("");

#!/bin/bash -e
#

set -E
set -o pipefail

if [ ! -x "$PWD/minio" ]; then
	echo "minio executable binary not found in current directory"
	exit 1
fi

WORK_DIR="$PWD/.verify-$RANDOM"
MINIO_CONFIG_DIR="$WORK_DIR/.minio"
MINIO=("$PWD/minio" --config-dir "$MINIO_CONFIG_DIR" server)

function start_minio_3_node() {
	export MINIO_ROOT_USER=minio
	export MINIO_ROOT_PASSWORD=minio123
	export MINIO_ERASURE_SET_DRIVE_COUNT=6

// Copyright 2010 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

package zip

import (
	"compress/flate"
	"errors"
	"io"
	"sync"
)

// A Compressor returns a new compressing writer, writing to w.
// The WriteCloser's Close method must be used to flush pending data to w.
// The Compressor itself must be safe to invoke from multiple goroutines

            duplicateHostList.addAll(duplicateHostService.getDuplicateHostList());
        } catch (final AutoBindingFailureException e) {
            logger.warn("DuplicateHostService is not found.", e);
        }
    }

    /**
     * Sets the list of duplicate host rules.
     *
     * @param duplicateHostList the list of duplicate host rules to use
     */

  private transient volatile @Nullable CacheEntry<K, V> cacheEntry2;

  MapRetrievalCache(Map<K, V> backingMap) {
    super(backingMap);
  }

  @SuppressWarnings("unchecked") // Safe because we only cast if key is found in map.
  @Override
  @Nullable V get(Object key) {
    checkNotNull(key);
    V value = getIfCached(key);
    if (value != null) {
      return value;
    }

    value = getWithoutCaching(key);

if defined JAVA_HOME goto findJavaFromJavaHome

set JAVA_EXE=java.exe
%JAVA_EXE% -version >NUL 2>&1
if %ERRORLEVEL% equ 0 goto execute

echo. 1>&2
echo ERROR: JAVA_HOME is not set and no 'java' command could be found in your PATH. 1>&2
echo. 1>&2
echo Please set the JAVA_HOME variable in your environment to match the 1>&2
echo location of your Java installation. 1>&2

goto fail

:findJavaFromJavaHome